Carrier transport, photonics and sensing in group IV-based and other semiconductors nanodevices

Resume : Two-dimensional (2D) materials are of great interest for use in ultimate-scaled transistors. In this talk, I will describe recent developments on three main types of 2D material electronic devices aimed at achieving enhanced performance MOSFETs. The first material is MoS2, which is ideal for use in dynamic memories due to its wide bandgap, heavy effective mass and scalability to ultra-small gate lengths. We have fabricated both one- and two-transistor DRAMs using MoS2 MOSFETs and demonstrated circuits with equivalent leakage currents as low as 1-2 fA/µm [1]. While ideal for low-leakage devices, it has been challenging to achieve high on-current devices based upon MoS2 and other transition metal dichalcogenides (TMDs), partially due to the high contact resistance. We have recently shown that improved contact resistance can be achieved using the polymorphic properties of TMDs, and we have specifically demonstrated MoTe2 MOSFETs with 1T’/2H homojunction contacts with lower barrier high and improved drive current compared to devices with metal/2H contacts [2]. Finally, we have utilized black phosphorus (BP) to realize tunneling field effect transistors (TFETs) which have the potential for sub-60-mV/decade subthreshold slope operation. BP, due to its anisotropic effect mass enables the realization of novel right-angle TFETs, which we have shown allows TFETs to achieve high on-current and low off-state leakage simultaneously [3]. This work was supported by DTRA HDTRA1-14-1-0042, NSF DMR-1420013, NSF ECCS-1708769, and NSF ECCS-1542202. [1] C. U. Kshirsagar, et al., ACS Nano 10, 8457 (2016); [2] R. Ma, et al., ACS Nano 13, 8035 (2019); [3] M. C. Robbins, et al., IEEE Elect. Dev. Lett. 40, 1988 (2019).

Resume : In recent years, the unique structural, electronic, and optical properties of graphene made this two-dimensional material an attractive subject of research. The linear dispersion of the Dirac electrons in graphene has been directly utilized for broadband optical absorption, although the photo-responsivity values of the resultant photodetectors were not high due to the high transparency of graphene. On the other hand, the high transparency of graphene over wide bandwidth of light led to many other forms of photodetectors. Graphene has been adopted to form transparent electrodes in various solar cells. It has also been combined with crystalline silicon (c-Si) to form Schottky photodiodes. While the usage of graphene in photodetection is quite clear and certain, the feasibility of using graphene for electroluminescence (EL) remains uncertain. Methods to create significant EL need to be explored and the corresponding light emission mechanisms require more study. Excluding the studies on the light emission from graphene quantum dots and reduced graphene oxides, there have been not many reports on the EL in graphene [1-4]. Not all of the reported methods are practical because either scanning tunneling microscope (STM) is needed for electron injection [2] or suspended graphene is required for thermal isolation [3]. And the wavelengths of the emitted lights in all these works majorly lie in the IR or near-IR range even though secondary and much smaller spectral peaks also appear in the visible light range. In the present work, a p+-Si/graphene/n+-Si diode was fabricated and we report our observation on the light emission from this structure. This work provides a simple way to obtain visible EL out of the graphene on silicon. On a silicon substrate, separate p+ and n+ regions were formed. Single-layer graphene was then transferred onto the substrate to partially cover the doped regions and to totally cover the region in-between. In this device, current flows horizontally in the graphene film. Visible white light was emitted and can be recorded by usual digital camera. Measured spectra of the emitted light show that, unlike the results in the previous works mentioned above, there is no spectral peak in the IR range. The largest peak lies at 670 nm wavelength, a smaller peak locates at 520 nm wavelength, and the third and smallest peak is at 420 nm wavelength. The intensity of the emitted visible light was found to increase with the supplied current. Interestingly, the light emission was observed to occur at the edge regions of graphene. When the device was forward biased, light emission occurred near the graphene edge at the p+-Si side. When the diode was reverse biased, reverse current flowed and light emission occurred at the graphene edge on the opposite side. Both light emissions showed the same spectral response. This phenomenon suggests that the observed light emission may be related to the accelerated electrons in the graphene and the defects at the graphene edges. [1] Essig S et al, “Phonon-assisted electroluminescence from metallic carbon nanotubes and graphene”, Nano Lett. 10, pp. 1589–94 (2010). [2] Beams R et al, “Electroluminescence from graphene excited by electron tunneling”, Nanotechnology 25, 055206 (2014). [3] Kim Y D et al, “Bright visible light emission from graphene”, Nature Nanotechnology 10, pp. 676–81 (2015). [4] Angela Beltaos et al, “Visible light emission in graphene field effect transistors”, Nano Futures 1, 025004 (2017).

Resume : Micro-crystals made of Ge/Si heterostructures can be used as absorbing elements for photodetection in the near-IR region. Ordered arrays of several micrometers tall Ge micro-crystals can be grown by Low-Energy Plasma-Enhanced CVD on Si substrates, deeply patterned by optical lithography and reactive ion etching. In such heterostructures the relatively large absorbing volume and light confinement effects, due to crystal faceting and pattern periodicity, enhance light absorption as compared to conventional epitaxial layers, making them well suited for photodetectors fabrication. The main challenge in realizing this type of devices is the formation of a top transparent contact suspended on the microcrystals array. Graphene can be used as a suspended contact that can adapt to the 3D-morphology of the microcrystals, ensuring the formation of an electrically continuous layer. A wet-transfer process has been developed to fabricate a highly transparent top contact on p-i-n doped Ge microcrystals. The fabricated devices have been characterized by means of electrical and optical measurements that confirm the near- IR photoresponse. Light-trapping effects on the responsivity, and their dependence on the pattern geometry and the micro-crystal morphology, are under investigation in a confocal microscope set-up.

Resume : Single and few-monolayer (s- and f-ML) graphene is often proposed as the field electrode in devices based on two-dimensional (2D) materials enabling the ultimate thickness scaling combined with excellent chemical and thermal stability. However, electron transport characteristics in these devices, e.g., in a tunnel transistor, depend critically on the effective workfunction (EWF) of the graphene electrode and its lateral uniformity. Potentially, the EWF of graphene may be influenced by a number of factors including the MLs number, the layer transfer method and subsequent annealing treatments which might affect, for instance, graphene doping. Here we used the wafer-scale CVD-grown s- and f-ML graphene of different thickness transferred onto SiO2 (50 nm)/p+-Si substrates to estimate the EWF variations using internal photoemission of electrons from the electron states near the graphene Fermi level into the oxide conduction band. The measured EWF of graphene shows only marginal changes (≈0.1-0.2 eV) depending on the ML number and the transfer induced interface contamination with water and hydrocarbons as influenced by the post-transfer anneal. The inferred EWF values (4.8-5.0 eV) are generally higher compared to vacuum WF of graphene (4.5 eV). These results allow us to suggest that systematic deviation of the graphene EWF on SiO2 from the vacuum value is caused by formation of polarization (charged) layer at the oxide surface rather than by variation of the graphene properties.

Resume : An uniaxial strain on the graphene induces a moving of Dirac points and the Dirac cones become anisotropic. We theoretically study the effect of the uniaxial strain on the electronic transport in the graphene. We focus on the effects of the uniaxial strain on the transmission across a potential barrier, on the conductivity as well as on the shot noise. We find that the conductivity along the strain axis increases with the strain modulus and decreases in the other direction. Particularly for clean and undoped graphene, the transport properties are similar to those of a diffusive metal with a Fano factor (the ratio of shot noise power and current) F=1/3. This transport regime in graphene, which is called pseudo-diffusive [1], is not restricted at the neutrality point but extends over a finite energy range around zero energy. We show that the strain leaves the Fano factor unchanged but affects the energy range which show pseudo-diffusive transport. [1] J. Tworzydlo, B. Trauzettel, M. Titov, A. Rycerz, and C. W. J.Beenakker, Phys. R ev. Lett. 96, 246802 (2006).

Resume : The increasing use of hydrogen (H2) as a clean energy carrier utilized in the next-generation fuels demand parallel development of low power hydrogen sensors (operated at room temperature) for safety purposes. In this work, we report a controlled single-step, large-area growth of vertically aligned edge-oriented MoS2 hybrid nanostructured thin film decorated with Pd nanoparticles (Pd/MoS2) on quartz and Si substrates using DC magnetron sputtering technique. The structural, morphological and chemical characterizations were performed using XRD, Raman, FESEM, TEM, EDX and XPS techniques, which confirms the formation of Pd/MoS2 hybrid thin film. To fabricate the Pd/MoS2 gas sensor, a patterned deposition of the Ag contact electrode on the top of Pd/MoS2 was performed by sputtering through a shadow mask. Hydrogen gas sensing characteristics of Pd/MoS2 hybrid thin film sensor under low detection range (10-500 ppm) and proposed sensing mechanism are discussed in detail. To gain further insights into the gas sensing mechanism, we have studied the junction band alignment at the Pd/MoS2 interface using ultraviolet photoelectron spectroscopy and ellipsometry. The Pd/MoS2 sensor shows good response ~34% and fast response/recovery time ~16 s/38 s, higher selectivity towards 500 ppm H2 at room temperature (30 °C). Thus, this study offers the development of low power H2 sensors with enhanced sensor characteristics, which could be utilized in IoT (Internet of Things) network, with an advantage of facile and scalable fabrication techniques.

Resume : An electromagnetic mode without photonic excitations still has a non-zero energy of hv - called zero-point energy. The resulting vacuum field fluctuations give rise to long known physical effects such as the spontaneous emission, the Lamb shift and the Casimir effect. By engineering electromagnetic modes in cavities, vacuum can be made to interact with matter in the extensively studied weak, strong and ultrastrong light-matter coupling regimes [1]. The term ‘light-matter coupling’, as well as the optical experimental means by which the regime is usually studied, hides an important fact: vacuum alone gives rise to the coupling and not only alters the optical but also the material properties of the system. Already without photonic excitations and a large coupling strength, we can observe a coupling induced change to the matter part - a 2DEG - via a resistance measurement [2]. Hence, ‘Vacuum-matter coupling’ not only allows to engineer optical but also a variety of material properties. Concretely, we use a GaAs/AlGaAs-based Hall bar embedded in a microwave cavity. The latter couples ultrastrongly to the electrons at the Fermi energy that also contribute to transport. In presence of the vacuum field we find a clear reduction of the resistance at the maxima of the so called Shubnikov-de Haas oscillations [2]. This opens the way to vacuum-field-controlled many-body states in quantum Hall systems. [1] A. Kockum et al., Nat. Rev. Phys. 1, 19 (2019). [2] G. Paravicini-Bagliani et al., Nat. Phys. 13, 186 (2019).

Resume : Miniaturized low-cost/low power semiconductor sensors are of high demand in numerous emerging applications, in particular advanced smartphones, IoT systems and automotive electronics. The talk addresses the state of the art in integration of sensors with CMOS from the viewpoint of an analog semiconductor foundry. Integrated sensors that do not require additional masks , as well as devices that suppose small numbers of extra masks and wafer bonding, are discussed and compared with hybrid solutions, where sensing systems are built on interposers or printed boards. Special attention is given to matrix sensors, comprising large amounts of pixels, as well as sensors on SOI substrates. Smart sensors of UV radiation, Radon sensors and gas sensors of several types , all built within CMOS technologies, are described as examples. Challenges of introducing non-typical for semiconductor fabs materials are identified. As an example, gas sensor surface functionalization using shadow masks made of silicon is presented. Low neuron count neuromorphic blocks that allow preliminary signal processing from sensors are also analyzed and the developed memristive devices acting as synapses presented . These memristive devices use single Poly floating gate structures available in the core CMOS technology.

Resume : Transition metal dichalcogenides (TMDCs) have not only recently attracted tremendous at-tention due to their unique optical and electrical properties but also the interesting and various nanostructures created by different synthesis process. These atomically thin TMDCs materials possess great potential in sensing, optoelectronic, energy harvesting and Li-ion battery applica-tions. However, the atomic thickness of TMDCs will limit the light absorption and result in weak performance of optoelectronic devices, such as photodetectors. Here, we demonstrate a novel approach to increase the surface area of TMDCs in the one-step synthesis process of TMDC nanowalls from WOx into WS2 nanowalls. By utilizing the rapid heating and rapid cool-ing process, we can achieve the formation of nanowalls with the height of ~150 nm standing perpendicularly on top of the substrate. Our method provides a rapid synthesis process with enhanced aspect ratio compared to the conventional solid-vapor phase CVD process, which is commonly used for the synthesis of planar TMDCs with few atomic layers. Moreover, the combination of colloidal quantum dots (QDs) with three different emission wavelength and WS2 nanowalls will further improve the performance of WS2-based photodetector devices, in-cluding 3.5~4 times photocurrent enhancement and shorter response time. The remarkable re-sults of the QD-WS2 hybrid devices to the high NRET efficiency between QDs and our nanostructured material are caused by the spectral overlap between the emission of QDs and the absorption of WS2. Additionally, the outstanding NO2 gas-sensing properties of QDs/WS2 de-vices were demonstrated with a remarkably low detection limit down to 50 ppb with a fast re-sponse time of 26.8 s contributed by tremendous local p-n junctions generated from p-type WS2 nanowalls and n-type CdSe-ZnS QDs. Our work successfully reveals the energy transfer phenomenon in QD-WS2 hybrid devices and shows great potential in commercial multifunctional sensing applications.

Resume : In this work, Sn-doped indium oxide (ITO) nanowires with high density and high quality were synthesized via vapor-liquid-solid chemical vapor deposition (CVD) in a three zone horizontal tube furnace. Scanning electron microscopy studies show that the as-grown Sn-doped indium oxide nanowires possessed great morphology with an average diameter of 50 nm and length of about ten μm. High resolution transmission electron microscopy and x-ray diffraction studies were conducted to further identify the chemical composition, crystal structure and growth direction of the nanowires, which were confirmed to be Sn-doped indium oxide (c-In2O3) of a body-centered cubic structure. Also, we investigated optical and electrical properties of the nanowires with four-point probe, photoluminescence and UV-Vis spectroscopy. To improve sensitivity, Ag-doped ITO nanowires were synthesized by electrochemical deposition. Additionally, Gas nanosensors were designed and fabricated with a bottom-up approach in a FIB/SEM system based on an undoped and Ag-doped single ITO nanowire, respectively. This study is an important step towards the sensing of contaminated gases, contributing to better environment.

Resume : In direct monitoring of environment, gas sensors, particularly those based on solid state devices are commercially available and are widely used. In recent years, in addition to hazardous gas monitoring, new vistas for application are opening up for solid state gas sensors for use in healthcare such as exhaled breath analysis [1-2]. In this work we report a ZnO/silicon nanowires (ZnO/p-Si NWs) p-n hetero-junction array based nitric oxide (NO) gas sensor operating at room temperature with extremely high response (noise limited response ~ 10 ppb). The sensor shows very high selectivity towards NO gas sensing and limited perturbation in response due to presence of moisture. Utilization of cost effective chemical technique for fabrication of sensor on silicon is compatible with wafer level processing and easily connecting with silicon IC technology. The vertically aligned Si NWs array has been made by electroless etching method and the ZnO nanostructure was made by chemical solution deposition and spin-coating. The response is much enhanced in the p-n junction when the n-ZnO nanostructure interfaces with p-Si NW compared to that in the n-n junction formed by ZnO on n-Si NW. We observed that the heterostructure leads to a synergetic effect where the sensing response is more than the sum total of the individual components. Extensive cross-sectional electron microscopy and composition analysis by line EDS allowed us to make a physical model. The comparison of the simulation results with the experiment point out the device parameters that enhance the device response. The characteristics values of the parameters of ZnO/Si NWs heterojunction for the best fits obtained from the simulation and it can be seen that all the parameters undergo change in the electrical model and this leads to enhancement of current in the device on gas exposure [3]. References (1) A. Gas Sensors Based on One Dimensional Nanostructured Metal-Oxides: A Review, Arafat, M. M, Dinan, B; Akbar, S. A; Haseeb, A. S. M. Sensors 2012, 12, 7207-7258. (2) Low Power Consumption Gas Sensor Created from Silicon Nanowires/TiO2 Core−Shell Heterojunctions, Liu,D.; Lin,L.; Chen, Q.; Zhou, H.; Wu, J. ACS Sens. 2017, 2, 1491−1497. (3) ZnO/Si nanowires heterojunction array based nitric oxide (NO) gas sensor with noise-limited detectivity approaching 10ppb, Samanta, C.; Ghatak, A.; A. K. Roychaudhuri, A. K. ; Ghosh,B. Nanotechnology 2019, 30, 305501.

Resume : In the last decades, the demand for the development of sensors for the selective detection of volatile organic compounds (VOCs) operating at room temperature has been growing. For high-performance VOCs gas sensing applications, silicon based nanowires (SiNWs) are considered as one of the promising candidates. The compatibility with complementary metal oxide semiconductor (CMOS) processes and the possibility of high integration with advanced read-out circuits are major advantages. In this article, 220µm SiNWs with a 40x40nm cross-section have been fabricated. Their sensitivity to react on humidity, ethanol, and ammonia has been investigated. The electrical signal due to gas molecules interaction is obtained by analyzing the carrier transport through NWs operating as a back-gate transistor. The NWs were formed on Silicon on Insulator (SOI) wafers by using side-wall transfer lithography (SWTL) and functionalized by different oxides e.g. HfO2, ZrO2, and TiO2. In order to decrease the contact resistance, NiPt silicide was formed prior to Ti/ Al metal contact deposition. Four contact electrodes were formed to the NWs to obtain a better estimation of the NWs’ resistance and the contact resistance. The mechanism of gas sensing and their behavior in response to oxide material, and oxide thickness have been investigated in detail. This work demonstrates a low power device, working at room temperature, for selective gas sensing.

Resume : Transition metal oxide thin films find applications in electrochemical energy saving, generation, and storage devices. Electrode layer is an important component in electrochemical devices and in the present work, the electrochemical properties of V2O5, WO3 and multi-layer films have been studied for application as electrode layers. V2O5, WO3, V2O5/WO3 and V2O5/WO3/V2O5/WO3 thin film samples were fabricated by reactive dc magnetron sputtering on Fluorinated Tin Oxide (FTO) substrates at 400oC. X-ray diffraction studies confirmed the formation of orthorhombic V2O5 and monoclinic WO3 films with (001) and (002) preferred orientation respectively. Raman studies support the results obtained from XRD. Field emission scanning electron microscopy (FESEM) was used to study the surface morphology of the films. UV-vis spectroscopy showed V2O5/WO3/V2O5/WO3 sample had the highest transmittance. The cyclic voltammetry (CV) studies were performed at three scan rates: 10 mVs-1, 100 mVs-1 and 500 mVs-1. The diffusion constant for H was calculated from CV data and showed a decrease with increase in the scan rate for all samples except for V2O5/WO3 sample. At each scan rate the diffusion constant was highest for V2O5/WO3/V2O5/WO3 and the values were 7.37×10-14 cm2s-1, 2.35×10-14 cm2s-1, 1.40×10-14 cm2s-1 for scan rates of 10 mVs-1, 100 mVs-1 and 500 mVs-1 respectively. The highest value of interfacial capacitance (1165 mFcm-2) among all the samples was found for V2O5/WO3/V2O5/WO3 at a scan rate of 10 mVs-1. This study suggests that V2O5/WO3/V2O5/WO3 sample has significantly improved electrochemical properties as compared to the individual films along with good optical transmittance.

Resume : The efficient detection of moving fluorescent agents, such as molecular motor-driven cytoskeletal filaments, is important for the design and operation of molecular diagnostics and biocomputation devices. GaP-nanowires have recently been identified as promising elements for biosensing applications mainly due to their light-guiding properties. Here, we investigate how GaP-nanowires deposited on a glass surface collect and guide light of fluorescently labelled cytoskeletal filaments. Specifically, microtubules with fluorescent extensions of different length were prepared. When a microtubule passed the GaP-nanowire in close proximity, fluorescent light locally coupled into the nanowire, was internally guided and eventually emitted at the nanowire tip up to 5 µm away from the position where the microtubule passed the nanowire. We evaluated the signal intensities in terms of waveguide losses and size of fluorescent microtubule extensions. Our approach allows to separate the location of signal detection from the actual point of interaction between entities of interest and will therefore increase the freedom in the design of future nanodevices. Funding: H2020 Bio4Comp, GA No: 732482, Volkswagen Foundation, GA No: 93440

Resume : Recently, AlGaInP-based light-emitting diodes (LEDs) have experienced an impressive evolution in both device performance and market volume. In particular, high-brightness LEDs are gaining interest for use in commercial applications such as automotive lighting, full-color displays, and general illumination. To enlarge their utility in new applications such as sensors, optical gyroscopes and lighting sources for plant factory, improved performances such as high optical power and broadband spectrum have been pursued. The short coherence length related to a broad bandwidth allows the realization of devices with significantly improved sensitivity. AlGaInP-based LED structures usually require a larger active volume in order to prevent carrier overflow and to attain a higher spontaneously emitting light output power. To enlarge the active volume, the same energy band structures of wells and barriers are usually multi-stacked. So, AlGaInP-based LED structures emit a relatively narrower spectrum having less than 20 nm of the full width at half maximum (FWHM). For the broadband spectrum, it is necessary to make irregular energy band structures in the active region by introducing chirped quantum-well (QW) structures. But, in the AlGaInP-based LEDs having a multi-quantum well (MQW) structure, the effects of the chirped QW structures on LED performance have not been systematically studied until recently. In this study, we investigate the behaviors of optical and electrical characteristics according to the change of well thicknesses in MQW LED structures through an analysis of temperature dependent photoluminescence (TD-PL) data and device performances.

Resume : Solar energy conversion into hydrogen energy via photoelectrochemical (PEC) water splitting is one of the most promising ways. Due to the kinetic problems, water oxidation is the bottleneck. In recent years, photoanodes made from earth abundant elements with high efficiencies have been developed. Modification methods like doping, nanostructuring, co-catalysing and forming heterojunction etc have been used to improve the efficiencies. However, the charge dynamics in the photoanode is not generally studied. Bismuth vanadate (BiVO4) has been a widely studied n-type semiconductor for water oxidation. Here, we use BiVO4 as a model to study the influences on the charge dynamics after doping by molybdenum (Mo) and forming heterojunction with tungsten trioxide (WO3) via transient absorption spectroscopy (TAS) in both slow and ultrafast timescales for the whole lifetime of photoexcited holes from generation to recombination. The decays of the transient current signal will be used as complement. The bare BiVO4 and Mo doped BiVO4 (a series of doping levels) photoanodes will be prepared via aerosol-assisted chemical vapour deposition (AA-CVD) on fluorine doped tin oxide (FTO) to study the doping effect. Furthermore, both plane and nanostructured (nano-needles) WO3 substrates will be used to study the effect of forming heterojunction. Our result will provide an insight of modification effects on n-type semiconductors for water oxidation.

Resume : Silicon-germanium with diffused lithium atoms is considered as X-ray detector. Compared to Si(Li) it has potential advantages. The main one is a much higher atomic number that provides a significant increase in absorption efficiency. In this study Czochralski grown silicon-germanium single crystals were used. It is known that bulk SiGe is difficult to grow because of the segregation of germanium. Crystals grown by the Float Zone technique are only available in small sizes. The Czochralski method allows the growth of large crystals, but with a lower resistivity. Lithium atoms in the SiGe bulk help solve this problem. The paper mainly considers the processes of lithium diffusion and drift. Few methods were used to control the depth of diffusion. One of the methods (AFM measurement of surface potential) was improved by us for more convenient use and more accurate measurements. The dependence of the diffusion coefficient of lithium on the concentration of germanium was also investigated. Some aspects of crystal treatment, diffusion and subsequent drift processes are considered to optimize detector characteristics.

Resume : Waveguide with low energy loss is a crucial point for integration of photonic components. Si has been commonly used as waveguide material in near infrared (NIR) region. In this work, SiNx layers are proposed as an excellent waveguide material. For this application, the thickness of SiNx layer has to be minimum 500 nm to confine the light properly. Meanwhile, to obtain such layer thickness is a difficult task due to internal stress in SiNx which leads to cracking the layer. Therefore, SiNx layers were patterned and later carefully cycle annealed. The patterned SiNx layer can effectively release the stress compared to annealing the whole layer. Rapid thermal chemical vapor deposition (RTCVD) technique was applied to grow SiNx layers where in-situ Steam Generator (ISSG) process was also applied to minimize the sidewall roughness of Si3N4 waveguide prior to deposition of SiO2 cladding layer. After a full process optimization, the Si3N4 waveguides demonstrated a minimum optical loss of ~0.5dB/cm with a peak coupling efficiency of 7dB.

Resume : Si-based multiwavelength light sources are of great interest for applications in photonics and multiplexed signal communication. The realization of an innovative hybrid light source operating at room temperature, obtained by embedding a carbon nanotube (CNT) dispersion inside a Si nanowire (NW) array is reported. Ultrathin Si nanowires (NWs) synthesized by metal assisted chemical wet etching using a very thin discontinuous Au layer as precursor were used as platform and coated with debundled single walled carbon nanotube (CNT) dispersions. A bright room temperature emission in the visible range due to electron–hole recombination in quantum confined Si NWs is reported. The hybrid Si NW/CNT system exhibits a room temperature simultaneous emission both in the visible (due to Si NWs) and the IR (due to CNTs) ranges, thus demonstrating the realization of a low-cost material with promising perspectives for applications in Si-based photonics. The detailed study of the optical properties of the hybrid system evidences that the ratio between the intensity of the visible and the IR emissions can be varied within a wide range by changing the excitation wavelength or the CNT concentration and the conditions leading to the prevalence of one signal with respect to the other were investigated. The multiplicity of emission spectra obtainable from this composite material opens new perspectives for Si nanostructures as active medium in light sources for Si photonics applications.

Resume : Semiconductor NWs have been proven to be useful as basic building blocks for photonic components, including lasers, detectors, modulators and solar cells. Silicon is the most important semiconductor and the possibility to obtain an efficient room temperature light emission from Si NWs would represent an important advancement in photonics. In spite of this great potential interest, light emission from Si NWs is still a scarcely reported and unexplained phenomenon. We will present a new approach for Si NWs synthesis, based on a metal-assisted wet etching process. The process is simple, cheap, fast, compatible with Si technology and, above all, able to synthesize Si NWs exhibiting a strong room temperature photoluminescence (PL). We will present a detailed analysis of the steady-state and time-resolved PL properties of the system as a function of aging, temperature and pump power to demonstrate that the emission is due to the occurrence of quantum confinement effects. Moreover, we will present a prototype device based on Si NWs exhibiting a strong and stable room temperature electroluminescence at operating voltages as low as 2 V. These results open the route towards novel photonic applications of silicon NWs as efficient light sources.

Resume : Semiconductor nanowires (NW) are of great impact as new materials for a broad range of applications. High-density arrays of ultra thin Si NWs with tunable aspect ratio were realized at low cost by metal-assisted chemical etching. By using Au layers with fractal arrangement, we engineered the synthesis of 2D random fractal arrays of vertically aligned Si NWs realized without any mask or lithography. By optimizing the size and spatial arrangement of NW fractals, we can tune the optical response of the system. Strong in-plane multiple scattering and efficient light trapping overall the visible range were observed due to the fractal structure(1), remarking the promising potential of Si NWs for photovoltaic and photonics. NWs achieved by this technique have the same structure and doping of the starting Si bulk, exhibiting a very bright room temperature PL tunable with NW size according to quantum confinement. Light emitting devices based on Si NWs showing an efficient room temperature EL emission at low voltage were reported. We demonstrate the first experimental observation of Raman coherent backscattering arising from the constructive interference of inelastically scattered Raman radiation in strongly diffusing Si NWs. The RCBS results are interpreted with a model of mixed Rayleigh-Raman random walks, exploiting the role of phase coherence in multiple scattering phenomena. 1. Light: Science & Applications 5 (4), e16062, 2016 2. Nature Photonics 11, 170, 2017

Resume : As an important III–V ternary semiconductor, InGaAs are expected to have potential bandgap tunability from the near-infrared (NIR) to mid-infrared (MIR) region (0.35 eV≤ Eg ≤1.42 eV). Due to its tunable bandgap, as well as high electron mobility and small leakage current, InxGa1-xAs nanowires have been widely used in optoelectronic devices, such as NIR emission lasers, photovoltaics, and field-effect transistors. We applied a chemical vapor deposition method to grow single-crystal InGaAs nanowires on amorphous SiO2/Si substrates via two steps. An then photodetectors based on as-grown InGaAs nanowires were also constructed, which show good light response at the wavelength of 1550nm. This photodetector may have potential applications in integrated optoelectronic devices and systems.

Resume : This work aims to investigate the performance of a new Junctionless (JL) Ge-gate Tunneling-FET phototransistor for Infrared sensing applications. The electrical and optical performances of the considered sensor are numerically analyzed, where both switching and optoelectronic properties are reported. In this context, we address the influence of the Ge-gate doping level and high-k gate dielectric on the variation of optical Figures of Merit (FoM) parameters such as responsivity, ION/IOFF ratio and optical commutation speed. Interestingly, it was revealed that the proposed design provides promising pathways for enhancing the phototransistor FoMs as compared to the conventional FET-based sensors. In the second stage of our investigation, we provide a performance assessment of the proposed phototransistor by analyzing its switching capabilities as compared to the conventional design, where the device is implemented in an optical inverter circuit. The obtained results indicate the superior optoelectronic performance offered by the proposed design in comparison with the conventional devices in terms of optical commutation speed and optoelectronic gain. Therefore, this contribution can provide more insights concerning the benefit of adopting JL-TFET design for future high-performance and ultra-low power deep submicron CMOS optoelectronic applications.

Resume : Two-dimensional (2D) materials have been extensively applied in electronic and optoelectronic devices due to their unique and extraordinary electrical and optical properties. Among them, tin disulfide (SnS2) has attracted enormous research interests due to their low-cost, earth-abundant, environment friendly properties as well as superior performance as photodetectors. Here, we demonstrate an outstanding in-plane SnS2 phototransistor with an out of plane built-in electric field enabled by MoO3 surface functionalization. The photocarriers are generated and effectively separated by the vertical electric field, leading to a high photoresponsivity of 2.3103 AW-1, photoconductive gain of >105, external quantum efficiency exceeding 8%. It also demonstrates a low noise power density, revealing an ultrasensitive photodetection with specific detectivity up to 3.21012 Jones. The formation of the out of plane built-in electric field is validated by the output electrical transport measurement of SnS2 vertical transistor, and further corroborated by in situ ultraviolet photoelectron spectroscopy and X-ray photoelectron spectroscopy characterizations. Our findings promise surface functionalization as an effective approach to induce an internal electric field in 2D multilayer SnS2 towards its application in high performance photodetection.

Resume : Harvesting the wasted heat energy from the vehicles, industries and other warm objects in our daily life has been the interest of thermoelectric research. Si nanowire has been proved to be an efficient TE material(Li, Wu et al. 2003). In this work, the effect of strain on the thermoelectric performance of Si nanowires has been investigated. The strain was induced by the deposition of SiNx layer on the Si NWs. The chip consisted of arrays of Si NWs of 30×30 nm2 in cross-section with integrated heater on both sides. The structure has been used in before researches (Boukai, Bunimovich et al. 2008). Unlike the traditional VLS-CVD approach for the Si nanowire growth, the Si NWs are fabricated in a top-down approach by combining the CMOS/MEMS fabrication technology. Sidewall transfer lithography（STL）is applied to the fabrication of Si NW(Hallstedt, Hellstrom et al. 2008), followed by nickel silicide and the metallization in a Ni/Ti/Pt sequence. A nitride layer is specially deposited before the NiPt silicide in order to prevent the Si layer from the metal deposition and decrease the contact resistance with the thermoelectric Si nanowire. By using a back-gate configuration and four contacts, the electrical behavior and hence TE properties of the Si NWs were characterized. The carrier transport in the NWs was altered by gate voltage under different temperature difference. The thermoelectric power factor shows an enhancement compared to other reported article over the temperature range of 273 K to 450 K.

Resume : Gallium oxide (Ga2O3) is a promising material for applications to high-power electronics and optics owing to its wide bandgap (4.8–4.9 eV) and low cost. In particular, its band gap characteristic is suitable for solar-blind photodetectors that can detect light in a deep ultraviolet (UV) region. Ga2O3 can effectively generate a photocurrent in the short-wavelength region, thereby eliminating unnecessary interference from visible and infrared wavelengths and detecting weak UV light efficiently. Until now, UV photodetectors have been demonstrated in the form of photoconductive, metal–semiconductor–metal, Schottky diodes, and heterojunction diodes. In this study, a β-Ga2O3 phototransistor is fabricated for UV detection, and modulation of its photocurrent using input radiation is demonstrated. The phototransistor is a back-gate structure with an active layer of β-Ga2O3 film deposited via sputtering followed by spin-on-glass doping. The carrier control in the channel of the device is critical for reducing the noise in the photodetector and improving the signal-to-noise ratio. We determine the optimal performance conditions by varying the gate voltage (Vg). We also demonstrate the positive threshold voltage (Vth > 0) operation characteristics of the phototransistor. The developed transistor is normally off, which is difficult to achieve in conventional Ga2O3-based transistors. In addition, we show the potential barrier control of the metal–semiconductor by controlling Vg; the photo-to-dark current ratio is maximized at the condition of Vg lower than Vth. Technology computer-aided design simulations are performed to understand the Vth shift behavior for the doping concentration and film thickness.

Resume : We have demonstrated an ultraviolet-assisted nanoimprint lithography (UV-NIL) assisted dry etching approach for wafer-scale surface nanostructures of high power AlGaInP-based red light-emitting diodes (LEDs). In this approach, the removal of n+-GaAs is integrated in the surface nanostructures. By fabricating hexagonal arrays of cone-shaped etch pits on the surface of LEDs with this approach, gradient effective–refractive-index, from n=3.4 (AlGaInP) to gradually approaching to n=1.0 (air), can be achieved to mitigate the emission loss due to total internal reflection and thus enhance the light extraction. Two types of wafer-scale LEDs were fabricated and studied in this work, FLAT-LEDs without any surface nanostructures and DRY-LEDs with surface nanostructures by dry etching of the AlGaInP layer through UV-NIL patterns. Wafer-scale DRY-LEDs with varied dry etching times, such as DRY1-LEDs (3.5 min), DRY2-LEDs (4.0 min), DRY3-LEDs (4.5 min), and DRY4-LEDs (5.0 min), were fabricated and evaluated. It was found that the DRY3-LEDs showed the highest average value of optical output power, 172 mW, at an injection current of 350 mA. Compared to the wafer-scale FLAT-LEDs, the wafer-scale DRY3-LEDs show 68.6 % light output power enhancement. The yield of chips with an optical output power of 120 mW and above was 0.3% (4 chips) and 90.1% (1441 chips) for FLAT-LEDs and DRY3-LEDs, respectively. Based on the results obtained in this work, it is anticipated that our surface nanostructures method, combined UV-NIL patterning and dry etching, can be successfully applied to the development of wafer-scale high power LEDs for the industrial mass production.

Resume : Thanks to the superior properties of Ⅲ/Ⅴ compound materials with direct band gap and high electron mobility, multitude of applications and advantages for optoelectronic devices could be achieved by the hetero-integration of Ⅲ-Ⅴ materials on Si substrates. Two schemes of heteroepitaxy of InP on Si substrates are developed in this study. Ge is used for buffer layer, which is grown in a reduced pressure chemical vapor deposition (RPCVD) system. Selective area growth (SAG) of InP is carried on by metal-organic chemical vapor deposition (MOCVD). These are both mainly introduced in two methods. The first method is global epitaxy of Ge is performed on 6° offcut Si substrates in order to form a prominent double-stepped Si surface that prevents antiphase-domains defects (APDs). The second way is selective epitaxy of Ge on normal Si substrates. SAG of InP is then carried out on the basis of two different starting surfaces of Ge. The main goals of this study were to enable the growth of high quality InP on Si for optoelectronic devices applied in optical communications as well as high-frequency and high-speed devices. These two approaches represent viable alternatives towards the realization of CMOS-compatible III-V integration and film stack for high-performance growth of InP monolithically based on Si. Acknowledgement This work was financially supported by the National Key Research and Development Program of China (Grant No. 2016YFA0301701) and Director Fund of the Institute of Microelectronics of the Chinese Academy of Sciences, which are acknowledged. References： [1] Loo R, Wang G, Orzali T, et al. (2012). Selective Area Growth of InP on On-Axis Si(001) Substrates with Low Antiphase Boundary Formation [J]. Ecs Transactions, 159(3), 260-265. [2] Radamson. H. H, Thylén. L. (2015) Monolithic Nanoscale Photonics—Electronics Integration in Silicon and Other Group IV Elements [M].Elsevier, Oxford, UK. ISBN: 978-0-12-419975-0, pp.64-84.

Resume : Germanium is a promising photonic material because its direct-to-indirect band separation is only 136meV at room temperature, which means it has possibility to be tuned to direct or quasi-direct band gap material. It is shown that adequate tensile strain and n-type doping in Ge are two key methods to adjust the Ge band structure to a direct band gap material. The extrinsic electrons from n-type doping fill the L valleys to the level of the Γ valley to compensate for the remaining energy difference, thereby facilitating direct band-gap emission. Until now, there have been many studies to achieve the heavily n-doped Ge. Compared with the implanted Ge films, the in-situ doping technique of naturally doped Ge films during the epitaxy process is another effective method, which can realize significant optical gain while avoiding damage to the quality of Ge crystal. In this paper, the properties of n-type Ge layers deposited on Si substrate with in-situ doping using reduced pressure chemical vapor deposition (RPCVD) or implantation technique are investigated. The n-type epitaxial Ge layers with different phosphorus concentrations were grown at 650 °C on the surface of p-type Ge grown at 400 °C on Si. The implantation was performed in two steps where a dose of 1×1015 cm-2 with energy of 18 keV was applied. In each step, a rapid thermal annealing (RTA) was performed to ensure the dopant activation. The Ge films were characterized by using X-ray diffraction (XRD), Secondary Ion Mass Spectrometry (SIMS), and photoluminescence measurements (PL). The grown Ge films demonstrated high epitaxial quality with top phosphorus doping concentration of 2×1019 cm-3 whereas the implanted ones could show higher phosphorous level up to 8×1019 cm-3. It was confirmed that the sheet resistance of Ge films decreased with the increase of the doping concentration, together with a red shift of the photoluminescence due to bandgap narrowing. These results are of great significance for guiding the growth of n-Ge epi-layer by in-situ doping technology. Acknowledgement This work was financially supported by the National Key Research and Development Program of China (Grant No. 2016YFA0301701) and Director Fund of the Institute of Microelectronics of the Chinese Academy of Sciences, which are acknowledged.

Resume : Over the years, infrared detectors have received a lot of attention due to their applications in the military and civilian fields. Common thermal materials for detectors include amorphous silicon, vanadium oxide and silicon germanium materials. With the development of CMOS process, silicon-germanium material has attracted a lot of interest because of its compatibility with the process. This study presents the feasibility, reliability and capability of using SiGe/Si Multilayer Structure (MLS) for detection of infrared radiation in range of 8-14μm. The detector consists of Si:B/intrinsic 4×(SiGe/Si)/Si:B structure where B concentration in Si:B layers is 1×1019cm-3 acting as contact layers. The detector pixels have 10, 20, 40, 60, 80 and 100 µm in diameter. The detectors are grown on SOI wafers. The SiGe/Si MLS were characterized by secondary ion mass spectroscopy (SIMS), high-resolution transmission electron microscopy (HRTEM), Atomic Force Microscope (AFM) and high-resolution x-ray diffraction techniques (HRXRD). The IR performance will be tested by connecting the detector pixels to the transistor chip for imaging. This research can offer CMOS compatible material for IR-detection for example for night vision camera application in near future. Acknowledgement National Key Research and Development Program of China” (2016YFA0301701), which are acknowledged.

Resume : Since a decade ago, GeSn material has attracted attention in photonic and electronic research due to its properties of indirect-to-direct transition as well high carrier mobility in CMOS. Although the material properties are excellent but deposition of highly strained GeSn (on Ge buffer on Si substrate) with high epitaxial quality is not an easy task due to low solubility (<1%) of Sn in Ge. This problem promotes the segregation of Sn during epitaxy of GeSn. This work presents a new method using RPCVD technique to grow GeSn alloys with high Sn content (> 18%). The growth temperature is in range of 265-330 ℃, and SnCl4 and GeH4 have used as reactant precursors. By changing the Sn component or strain amount, the bandgap of GeSn material can be adjustable. Later, heterostructures (GeSn/virtual Ge) are patterned to micro-disks and the Ge is selectively etched by using CF4 in inductively coupled plasma (ICP) tool. The strain relaxation in Ge is dependent on the lateral depth of Ge. In this work, GeSn micro-disks demonstrate strong photoluminescence at room temperature in short wavelength range. The strain in GeSn has also been modulated by bonding the grown layer to oxide wafer forming GeSnOI. In this process, the strength of mechanical pressure on GeSn material may adjust the strain in the layer. Further material analysis have also been performed by using HRXRD and HRTEM. The state-of-art material quality and the novel methods to modulate the strain in the GeSn layers provide opportunity to design advanced photonic components in near future.

Resume : Integrating GaAs-based device structures onto Si and Ge for infrared and terahertz photodetectors and lasers is growing fast during the recent years. This is due to the advantageous of GaAs platform to grow advanced photonic structures as well as direct bandgap behavior for operating at 850 to 1550nm in telecom. In this study, GaAs growth using MOCVD technique on prepared Ge buffer on Si substrates has been presented. Furthermore, the impact of surface roughness and epitaxial quality of Ge buffer on the quality of GaAs layers has been studied. The Ge buffer was deposited either on 6°off-cut Si wafers or by selectively area grown on the patterned ordinary (0°off-cut) Si wafers. In order to create a smooth interface Ge/GaAs, a chemical mechanical polish (CMP) step was performed on the Ge buffer layer. The growth of GaAs layers has three steps: a low-temperature step at 460℃，middle-temperature at 600℃ and a high-temperature step at 640℃. The results show that anti phase boundary (APD) always exists on normal Si substrates, but is diminished on 6°off-cut substrate, or SAG substrates. The quality of GaAs depends directly on the surface roughness. The GaAs layers were characterized by high-resolution x-ray diffraction techniques (HRXRD), photoluminescence (PL), scan electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). This study demonstrate how to manufacture large size of GaAs virtual substrates with smooth surface for future high volume mass production of photonic components.

Resume : Integration of plasmonic nanoparticles (PNPs) over semiconductor surface offers greater efficiencies in resulting optoelectronic devices via Local Surface Plasmon Resonance (LSPR). When surface plasmons (oscillating free electrons present at metal-dielectric interface) are excited at resonance incident wavelength, strong light scattering takes place with sharp absorption bands at resonance wavelengths and local field enhancement. However, light-matter interactions governed by PNPs are critically governed by the surface distribution of PNPs over semiconductor surface, which hasn’t been cleared to date. We report a systematic study depicting how the varying surface density of Silver (Ag) NPs over β-Ga2O3 surface influences the performance of fabricated solar-blind photodetector. Interestingly, remarkable transitions are found, where sparsely-spaced Ag PNPs decorated β-Ga2O3 device exhibits polarity reversion while tightly-spaced Ag PNPs sample deviates from traditional photodetector behaviour showing anomalous behaviour. According to the transient response of bare β-Ga2O3 photodetector device exhibit positive photo-response which switches to drastically improved (~20 times enhancement) negative photo-response with ultra-high responsivity of 107.47 A/W (at 5V) when decorated by sparsely-spaced Ag PNPs over β-Ga2O3 surface. Additionally, the device showed an ultra-high responsivity operating in self-powered mode, with highest reported responsivity of 4.29 mA/W to the best of our knowledge. Moreover, as the PNPs density is further increased, the photocurrent starts to decrease under irradiation, thus deviating from traditional photodetector behaviour. Finally, we proposed a unified systematic model rationalizing all observed phenomena while setting up the fundamental basis for potential future applications. Thus, we present first experimentally determined study that shows how changing plasmonic density can tune device performance showing different behaviours, i.e. reverse switchable and anomalous behaviour.

Resume : Two-dimensional p-type and n-type transition dichalcogenides (TMDs) have attracted a lot for atomically thin integrated electronic and opto-electronic devices. Up until now, the TMD p-n junction devices usually made by stacking exfoliated or several growth materials which need highly trained skills and are time-consuming process. Also, during the processes, because it is easy to be contaminated by polymers or chemicals, too hard to ensure good surface qualities. Therefore, direct growth of lateral and vertical heterostructures have been researched and successfully synthesized by epitaxial growth method. However, during the sequential growth, we must care optimized growth conditions in every step as well as change source. Here, we report the synthesis of direct growth ‘p (Nb doped WSe2) - n (MoSe2) lateral Junction’ on a silicon substrate with chemical vapor deposition in one-step. We intended partial doping in p-domain with Niobium in order to improve the rectification ability of the p-n junction. To start with, silicon substrates were coated with water soluble sources mixed with SMD (0.1M) : ANO (0.2g/60 ml) : AMT (0.1g/10 ml) : NaOH (0.1/60 ml) : Opti : H2O. Then, the coated substrate was oxidized at 450 degrees. Solid state selenium (Se) solid source is put near gas inlet for vapor source. Underflow of Ar and H2 gas, Se is delivered to a Silicon substrate coated with water-soluble sources. The height profile of the p-n hetero-structure flake was confirmed by measuring Atomic Force Microscope (AFM). 1.2 nm is corresponding to a monolayer of TMD. Clear lateral integrations of the heterostructure are verified in spatially resolved Raman and photoluminescence (PL) mapping and spectrum. In edge region, the main peak (247 cm-1) shows the characteristic of Wse2 Raman peak. Additionally, the minor peak (220 cm-1) corresponds to our CVD Nbse2 peaks (247 cm-1 and 220 cm-1). The PL peak on the edge is red-shifted about 10nm (22meV) indicating an enhancement of the free hole density in Wse2 along with niobium doping. In center portion, one main Raman peak indicating the characteristic of MoSe2 (242 cm-1). What’s more, XRD (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass spectroscopy) points at Nb, W and Mo peaks which validates the presence of each molecule. The electrical properties of the FET (field-effect transistor) channeled with ‘Nb doped WSe2 – MoSe2’ are measured. The transport characteristic of doped WSe2 exactly indicates p-type behavior. Also, analyzing log-scale output characteristic shows improved on-off ratios (~ 106) compared to our intrinsic CVD grown WSe2. The typical n-type behavior is seen at MoSe2 with 107 on-off ratios. What’ more junctions show well-defined p-n diode rectification (Ideality factor is 1.3 at 60 VG) and an ambipolar transport properties. By illuminating lasers into our qualified p-n junction diode region, we proved the high-performance optoelectronic device characteristics. The Photo-responsivity [A∙W^(-1)] and Detectivity [Jones] values were calculated by analyzing the w photocurrent measured according to the different laser wavelength (375, 458, 638 and 811nm) and power [μW ~ mW]. We obtained very high D values (detectivity) around 1017 ~ 1018 Jones. Our approach of direct and partially doped p-n diode allows easy fabrications of atomically thin integrated electronic and opto-electronic devices. Thus, in order to fabricate high-performance integrated opto-electronic devices, direct growth of highly qualified lateral or vertical heterostructure is indispensable.

Resume : Semiconductor nanostructures are attracting the interest of the scientific community due to their innovative properties and broad range of applications. Among others, silicon is the leading materials for its conduction, availability at low cost and advancement in its industrial processing. In particular, Si is extremely employed in microelectronics and despite the design of vertical architectures, the occurrence of delay, heating and quantum effects represent today a major limit for the performances of its devices. In this field, the novelty of Si quantum confinement nanostructures foster the perspective of light emission at room temperature for the realization of optoelectronic devices to be employed in integrated Si photonics. In this study, the structural features of fractal arrays of Si nanowires are correlated to their optical response. Indeed, highly efficient luminescent nanowires can be obtained with the chemical etching of Si from a thin discontinuous gold template, with processed that are at low cost and compatible with industrial scalable standard. Additionally, we investigated the luminescence of arrays of Si nanowires by cathodoluminescence achieving spectral resolution at the nanometer scale. Angular resolved cathodoluminescence demonstrated the presence of incoherent radiation emitted isotropically from the array attesting its robustness with respect to the electron beam. The combination of optical and electron microscopy investigation pave the way for a better understanding of the radiative mechanism occurring in nanostructured material in order to manipulate their performances in nanoscaled devices.

Resume : Using first principles DFT calculations we investigate the effect of electron and hole doping on the structural, electronic, magnetic and optical properties of ordered and disordered La 2 CoMnO 6 (LCMO). Hole doping is achieved by incorporating Sr at La sites of LCMO, whereas electron doping is simulated by considering O-site vacancies. Our calculations find that when 50% of the La ions are replaced by Sr ions(LaSrCoMnO 6 ), the Co ions (two per unit cell, Z=2) which were in 2+ charge state and high spin state (in LCMO) take up a mixed valence state, with one of the Co ions (Co3+ ) being in an intermediate spin state and the other in 2+ high spin state. The valence and spin state of Mn however remain unaltered. Antisite disorder (at Co/Mn sites) is also found to get enhanced with Sr doping. On the other hand, with electron doping, i.e, on introduction of vacancy at oxygen sites (La2CoMnO 6−δ , δ=0.8), the Mn ions which were in 4+ charge state transform to 3+ charge state in order to maintain the overall charge neutrality. Introduction of Sr in this system (LaSrCoMnO6−δ , δ=0.8) is found to further enhance anti-site disorder as compared to when there was no oxygen vacancy, which is expected to have significant influence on the magneto-dielectric and magnetocaloric properties of the system. Magnetic calculations show the ground state magnetic structure changes with disorder and vacancies present in the sample. Metal to insulator transition takes place after introduction of oxygen vacancies. Oxygen vacancies and disorder help to enhance the optical anisotropy and birefringes value of the system.

Resume : Doping engineering two-dimensional materials are attracting widespread interest due to the additional degree of freedom available to tailor the material property for a specific application. An InSe phototransistor possessing tunable ultra-high mobility by Sn-doping engineering is demonstrated here. A striking feature of the Sn doped InSe flakes is the reduction in oxide phase compared to undoped InSe which is validated by spectroscopic analyses. Hence, an increased lifetime due to the enhanced crystal quality, the carriers in the Sn doped InSe have mobility higher than in InSe. The internally boosted electrical properties of the doping engineered InSe flakes exhibit ultra-high mobility of 2560 ± 240 cm^2/Vs by suppressing the interfacial traps with substrate modification and channel encapsulation. As a phototransistor, the ultra-thin InSe flakes are highly sensitive with a detectivity of 10^14 Jones. It possesses large optical absorption with the application of gate voltage resulting in photoresponsivity and photo gain as 3 × 10^5 A/W and 0.5 × 10^6, respectively. The obtained results outperform all previously reported performance of InSe based devices. In addition, we demonstrate the piezo-phototronic property in the doping engineered InSe flakes on a flexible polyimide substrate. The piezoelectric property and changes in the bandgap of the material were carefully studied with several spectroscopic analysis under strained conditions. Interestingly, we discover that in the fabricated device, the dark and photocurrent can be increased under a tensile strain which shows a great promise for the design of strain sensor and photodetector. Thus, the doping engineered InSe layered semiconductor finds potential application in optoelectronics and meets the demand for faster electronic technology.

Resume : For end-of-the-roadmap devices, the gate will be wrapped around the channel (so-called gate-all-around – GAA - configuration) in order to assure optimal control of the short-channel effects. Different architectures are being considered, like horizontal stacked nanowires or nanosheets [1, 2] or vertical nanowires [3], with their advantages but also integration challenges. In addition, junctionless architectures are quite appealing due to the reduced process complexity with respect to traditional inversion-mode transistors. It is expected that carrier transport in the ultimate devices will be affected by ballistic and quantum confinement effects even at room temperature. This could be reflected in the corresponding low-frequency (LF) noise, a parameter that is extremely sensitive to carrier trapping and scattering phenomena [4]. In this paper, a review is given about the LF noise behaviour of GAA nanowire or nanosheet devices. It will be shown that the pre-dominant 1/f or flicker noise is mainly determined by the gate stack processing, including the metal gate. At the same time, the device architecture has a pronounced impact on the noise Power Spectral Density (PSD). Junctionless devices can exhibit lower 1/f noise PSD, especially when the channel is in the core of the nanowire, so that the carriers are more distant from the traps in the gate oxide. Moving from trigate FinFETs to single-gate nanowires, stacked double nanosheets and, finally, vertical nanowires yields an improvement in the 1/f noise. In the latter case, other more fundamental noise mechanisms (thermal noise,...) may start to dominate at lower gate voltages [5]. At the same time, a clear correlation between the processing-induced variation in the nanowire diameter and the static and noise performance will be demonstrated. Finally, generation-recombination (GR) events give rise to so-called Lorentzian noise contributions that can originate from traps in the gate oxide, at the interface or in the nanowire [6]. The features of such a Lorentzian can be employed to investigate the underlying defects. Guidelines will also be provided to distinguish GR noise due to defects in the gate oxide (so-called Random Telegraph Noise - RTS) from RTS originating from traps in the semiconductor channel. References [1] A. Veloso et al., Tech. Dig. Symposium on VLSI Technol., p. 138 (2016). [2] A. Veloso et al., J. Phys.: Condens. Matter, vol. 30, p. 384002 (2018). [3] A. Veloso et al., to be published in the Proc. IEDM 2019. [4] E. Simoen, H.-C. Lin, A. Alian, G. Brammertz, C. Merckling, J. Mitard and C. Claeys, IEEE Trans. Device and Mater. Reliability, vol. 13, p. 444 (2013). [5] E. Simoen et al., Invited paper to be published in the Proc. EUROSOI/ULIS 2020. [6] D. Boudier, B. Cretu, E. Simoen, R. Carin, A. Veloso, N. Collaert and A. Thean, Solid-State Electron., vol. 128, p. 109 (2017).

Resume : The simulation of large atomistic systems, bulk, surfaces, or nano clusters, poses a significant computational challenge. Specifically, the modeling of sensors, often requires the simulation of adsorption of molecules on surface cells with a large number of atoms. Quantum methods such as Density Functional Theory (DFT) are accurate but are limited in the number of atoms and structures that can be examined. Classical Molecular Dynamics (MD) allows to simulate a large number of atoms in close to experimental conditions but has less accurate models for the forces between the atoms. In this work we present a Deep Learning (DL) model for the forces that gives a close to DFT accuracy but with the ability to model large atomic systems with a large number of possible configurations. We demonstrate this with models of Al, Na, Si, Ge, and Sn, for bulk, surfaces, and nano-clusters. We first show that in all systems we get a sufficient accuracy at much higher speeds. We also show that our model reproduces reasonably well the phonon spectrum for the different materials and the derived thermal properties in the quasi-harmonic approximation. We then show examples of simulations that we make with this models for large systems such as surface ad-atoms, surface adsorption problems, and MD simulations of nano-clusters.

Resume : Alongside indium gallium zinc oxide (IGZO), many oxides have been investigated for the past 16 years. Whether amorphous or polycrystalline, oxide semiconductors have demonstrated their potential use for large area electronics such as Active Matrix Organic Light Emitting Diodes (AMOLED) and other flexible and transparent electronics. Vacuum and non vacuum processes have been investigated for devices including diodes and thin film transistors (TFTs).Nevertheless, because IGZO use scarce and costly materials, and use many atoms, other more simple semiconductors may be viewed as a replacement. We propose tin oxide in its amorphous phase (a-SnOx). The devices combines abundant atom and simple solution process for TFTs reaching high mobilities. With Al2O3 or HfO2 as the gate dielectric, the field effect mobility reaches at least 50cm2/Vs. We demonstrate the stability over gate bias stress and under visible light. a-SnOx demonstrate high performance and high stability among common stressors making it a candidate for future large area electronics.

Resume : Qubits based on semiconductor quantum dots have made considerable progress in recent years. Single electron spin qubit, single charge qubit, or single spin-charge hybrid qubit, have been demonstrated in both GaAs and silicon devices. Strongly coupled two qubits have also been realized in either spin or charge qubit systems. Principally these achievements could be utilized to build up any quantum operations. In this talk we firstly report some experimental progress based on charge qubits such as the ultrafast universal quantum control of a single charge qubit using LZS interference, the controlled-NOT gate of two strongly coupled charge qubits and the three-qubit Toffoli gate. The realization of more sophisticated quantum logic gates will make quantum computation more effective, and hence relieve the requirement of quantum error correction when performing multiple quantum logic gates. Moreover, we also report some experimental progress based on hybrid qubit and spin qubit. Such as a tunable hybrid qubit in the GaAs double quantum dots, spin relaxation rate T1^-1 as a function of magnetic field strength under different valley-splittings in Si MOS quantum dot, fast Rabi oscillations of hole spins in Ge nanowires, the realization of a coupling between charge qubit to superconducting resonators.

Resume : Epitaxy of structures, made by layers of IV-group materials, is and will be extensively used as a fabrication process of nano-electronic and opto-electronic devices. For example, raised source/drain layers for both N-type and P-type Metal Oxide Semiconductor (MOS) structures are currently epitaxially grown in advanced devices such as Fin shaped Field Effect Transistors and epitaxial growths are also expected to be used in future lateral and vertical Gate All Around devices. Here we present a stochastic simulation method, based on augmented lattice, implemented to study at an atomic resolution the epitaxy in group IV elements, alloys and compounds. Formalization, implementation and (ab-initio based) calibration approached will be discussed in the details. Key features of our numerical tool is the prediction of the dependence on process-related parameters of several characteristics of the epitaxial process qualification such as local doping level, local alloys mole fraction, point and extended defect generation and evolution. In particular, the simulations can describe the morphology of the crystal nano-structures and the generation/evolution of the crystalline and composition inhomogeneities as a function of the initial sample condition and the process parameters. We discuss and compare model predictions with the compositional and structural characterization of experimentally processed samples.

Resume : We propose a first-principles atomistic method based on density functional theory and the non-equilibrium Green’s-function method to investigate the electronic and structural response of metal-insulator-metal capacitors under applied bias voltages. We validate our method by showing its usefulness in two paradigmatic cases where including finite-bias structural relaxation effects is critical to describe the device behavior: formation of dielectric dead layers in a paraelectric SRO|STO|SRO capacitor due to an applied bias voltage, and the switching behavior of a ferroelectric SRO|BTO|SRO capacitor due to an external electric field.

Resume : Silicon microfabrication technologies, which has enabled the integration of billions of transistors on a single chip for use in computers or in mobile phones, are now reaching dimensions of only a few nanometers – almost the size of biomolecules. Nano-scaled devices therefore enable sensing of proteins or DNA at very low concentration in a liquid solution, sometimes down to the single molecule level. At the same time, integration of hundreds of such sensors on a single chip properly functionalized with different antibodies would allow a full palette of different proteins or DNA strands to be sensed targeting a particular medical situation or diagnosis. In this talk I will review three different chip-based sensors which we have explored in various collaborative projects: (i) Nanowire (or nanoribbon) sensors. This is an electrical sensor working essentially as a MOS transistor with an open gate, onto which antibodies have been immobilized, sensing the charge of hybridizing proteins or DNA. (ii) Electro-kinetic capillary sensor. This uses a capillary with functionalized inner surface. By flowing the electrolyte solution through the capillary, an electrokinetic potential is generated which changes upon binding of target molecules. (iii) Finally, a membrane with nanopores has been used for translocating DNA strands labelled with fluorophores. This is an optical technique that allows single molecule detection where the throughput can be relatively large due to parallel DNA translocation in a large array of nanopores. Results and applications of these techniques will be reviewed.

Resume : Silicon nanowires (Si NWs) are becoming a building block for a wide application range, from energetics to photonics and biosensing. However, common synthesis methods as Vapor-Liquid-Solid (VLS) or Reactive Ion etching suffer of different limitations on the size, and for the VLS, on doping and impurities. By using a Metal-Assisted Chemical Etching approach, we realized quantum confined and room temperature (RT) luminescent Si NWs without the presence of any Au impurities [1-2]. Si NWs exhibit a huge aspect ratio arising as a perfect candidate for the realization of a sensing device. The realization of a new class of label-free PL sensors based on Si NWs for protein and DNA is shown. In particular, we realized a high selective sensor for C-reactive protein (crucial for heart-failure pathology) with a fM sensitivity that permits a non-invasive analysis in saliva [3]. By another functionalization protocol, we realized a selective label- and PCR-free sensor able to reveal few copies of Hepatitis B Virus without DNA amplification [4]. Finally, our preliminary results on the possibility, by using a Si NWs platform, to selectively detect exosome among other vescicles and with sensitivity surpassing standard approaches as nanotracking analysis and dynamic light scattering. All the adopted functionalization are Si industry compatible and flexible for different bio-targets. Si NWs luminescent sensors pave the way towards new cheap optical label-free sensors for the primary health care diagnosis with a Si industrially compatible approach. [1] B. Fazio, Light: Science & Applications 5 (2016) e16062. [2]B. Fazio, Nature Photonics 11 (2017) 170–176. [3] A. Irrera, ACS Photonics 5 (2018), 471–479. [4] A. A. Leonardi, ACS Sensors 3 (2018), 1690–1697.

Resume : Biocompatibility and bioactivity of silicon (Si) nanoparticles (NPs) in the whole life circle of Drosophila Melanogaster of different lines were investigated. Si-NPs were prepared by mechanical grinding of crystalline silicon (c-Si) and porous silicon (PSi), correspondingly. Aqueous suspensions of c-Si- and PSi-NPs have been added to food of the flies and were tested in different concentrations from 0.065 to 0.26 mg/mL. A positive effect of the both types of NPs was found for the lifespan of Drosophila flies, and the lifespan extension was more pronounced in the case of PSi-NPs. The presence of PSi-NPs in feeding media was found to result in the growth by 30-50% of the fertility of flies. The fertility grows was observed in the both observed lines. PSi-NPs were found to provide stronger positive effect of the lifespan and fertility of the flies, which were explained by epigenetic effects related to biodegradation of those NPs.

Resume : In recent years, bound states in continuum (BICs) have gained increasing attention in optics. Their capability of continuously changing between a bound state and the radiation continuum opens up a platform for highly sensitive light detection and manipulation. So far, BICs have only been experimentally demonstrated with purely dielectric systems of limited sensitivity. Here it is demonstrated that, in contrast to conventional optics, hybrid plasmonics via coupling of dielectric and plasmonic modes pave the way for BICs with far better light manipulation and detection capabilities. With the help of an analytic scattering matrix formalism and RCWA simulations we theoretically show that light diffracted by bound states in continuum benefits from the large sensitivity of the surface plasmons and the diverging radiative quality factor of the BIC at the same time, outperforming both purely dielectric and plasmonic BICs. These theoretical considerations are transferred to a specific symmetric hybrid waveguide design supporting topologically protected hybrid BICs. By using a modular low-cost polymer based fabrication technology and standard metallization techniques, we experimentally realize such a symmetric hybrid waveguide and demonstrate the first experimental evidence of hybrid BICs. We believe that hybrid BICs as well as the demonstrated fabrication technique show a new path to enhancing photonics with hybrid optics and enable efficient low-cost sensors and modulators.

Resume : For centuries, investigation of materials by means of optical microscopy and spectroscopy has been one of the most important methods to characterize the fundamental properties and characteristics of solid matter. However, the resolution of conventional optical microscopy is restricted by a diffraction related limitation and today, in the era of nanotechnology, it is important to have a proper tools for nanoscale investigations. Scattering scanning near-field microscopy (s-SNOM) is a method that circumvents a fundamental resolution limit by creating a nano-focus at the apex of a metal AFM tip, confining the light–matter interaction to the tip-sized near-field. We implement this principle in our neaSNOM near-field microscope in a way that makes it possible to utilize light from the visible and IR up to THz regions to probe nanoscale phenomena. Our interferometric detection method allows us to detect both optical amplitude and phase at the same time and efficiently suppress background. Interferometric methods allow background-free monochromatic optical mapping as well as broadband nano-FTIR spectroscopy, both at AFM resolution. This talk will show how this AFM-based method can be used for correlative nanoscopy to combine optical imaging and spectroscopy with standard scanning probe modes to extensively characterize matter. The broad-band optics make it possible to perform optical correlation at different wavelengths and the AFM platform enables the correlation of these optical images with other data channels, such as AFM topography, as well as more specialized AFM modes, such as Kelvin probe force microscopy (KPFM). Examples of such a correlation can be SRAM test structures. The different doping concentrations and the charge carrier density and potential inhomogeneity can be imaged along with surface work function, IR and THz near-field reflectivity. With the ability to determine the charge carrier concentration in a contact-free manner from s-SNOM images these correlative measurements can be used for a comprehensive characterization of the surface and nanostructure electronic properties.

Resume : Photonic annealing which could stand as a more common synonym for flash lamp annealing, photonic curing, laser annealing etc. is established now as a key technology for advanced thermal processing of modern materials classes like semiconductors, high-k-materials, TCO’s, printed electronics, flexible substrates etc. In this talk examples of recent research activities at the Helmholtz-Zentrum Dresden-Rossendorf will be presented to convince the auditorium of the new and fascinating chances using annealing steps in the time range of milliseconds and below. Processes like dopant activation, crystallization as well as recrystallization effects, suppression of diffusion and segregation, surpassing the limits of solubility etc. will be demonstrated with selected examples.

Resume : Doping of semiconductor nanostructures, especially silicon nanocrystals (Si-ncs), became one of the most attractive research activity for the development of new plasmonic devices. In fact, providing charged carriers by introducing n or p type impurities in Si-ncs should induce the manifestation of Localized Surface Plasmon Resonance (LSPR). Compared to metals, the major advantage of using doped semiconductors is the possibility to tune the LSPR by controlling the carrier density. Before reaching these properties, one of the most challenging task consist in performing an effective doping of such low dimensional structures. In fact, due to the low solubility of impurities in silicon, surface defects or self-purification, performing high doping in a Si-nc could be difficult. To improve the quality of these systems, a precise control of the location and of the electrical activity of impurities is necessary. In this work, we performed a deep structural analysis of P doping of Si-ncs embedded in SiO2, elaborated with different elaboration process, by using Atom Probe Tomography. In the case of doping, it gives a unique opportunity to perform 3D mapping at the atomic scale to investigate the precise location of impurities and Si clustering characteristics. We evidenced the introduction of P in the core of Si-ncs allowing a high doping of these nanostructures. This seems to reveal a similar mechanism of impurities introduction in Si-ncs, independently of the elaboration process.

Resume : Performing effective doping of silicon nanocrystals (Si-ncs) embedded in SiO2 became a relevant subject in order to develop new plasmonic devices. In semiconductors, a perfect control of the charge density allows to tune the spectral position of the Localized Surface Plasmon Resonance. It has been shown that, depending of the elaboration conditions and their environments, P or B doped Si-ncs can exhibit a plasmon resonance. However, in low dimensional systems, the position of the impurity (in the core of Si-ncs, at the Si/SiO2 interface or in the surrounding matrix) can strongly affect these properties. Therefore a precise control of the location of impurities is necessary. In this work, P and B doped Si-ncs embedded in SiO2, elaborated by ion implantation, have been investigated using Atom Probe Tomography. This technic allowed us to perform 3D mapping at the atomic scale to investigate the precise location of impurities and the Si clustering characteristics. We evidenced a clear difference on the location of impurities in Si-ncs. On one hand, P atoms are efficiently introduced in the core of every single Si-ncs allowing a high doping of these Si-ncs. On the other hand, B atoms remain in majority in the matrix, at the Si-nc/SiO2 interfaces or in shells surrounding Si-ncs. Finally, photoluminescence measurements highlight that in P as in B doped Si-ncs, these locations of impurities lead to a quenching of the Si-ncs luminescence.

Resume : Shallow gap states are generally expected to trap charge carriers in dielectric films like high-permittivity oxide insulators thus affecting operation of field-effect devices on a short time scale or at low temperature. However, evaluation of their density and energy distribution cannot follow the conventional route because of fast electron de-trapping. In this work we present the approach to characterization of shallow traps in insulating films using their filling by electron tunneling pulses in Si/SiO2/oxide stack al low temperature (77 K) followed by thermally-induced de-trapping when temperature is ramped up. We compared two families of high-permittivity oxide insulators: HfO2 including Al- or Si-stabilized ferroelectric films, and LaSiOx with La content between 33 and 58 %. In both cases the density of electron traps filled at 77 K is nearly by one order of magnitude higher than the density of charge trapped at 300 K and corresponds to the volume trap concentration in the range of 10^19 cm-3. Most of the trapped electrons (>80 %) are removed from the oxide upon heating to 300 K. From the temperature dependence of the de-trapping rate the activation energies of 0.3-0.5 eV were inferred. However, since noticeable electron de-trapping is also observed at 77 K, there is probably a ≈1 eV wide continuous energy distribution of trap levels below the oxide conduction band edge resembling “band tail” states in disordered solids.

Resume : In solar water-splitting devices, revealing the effect of defect states on photoconversion is of paramount importance for the development of efficient photoelectrodes. Here, we designed a pump-push-photocurrent (PPPC) technique capable of tracking the dynamics of trapped carriers, in-situ, on the ps-to-ms time domain. A photoelectrochemical cell (PEC) with monoclinic BiVO4 as the photoanode was selected as a model system. This metal oxide is a promising photoanode for water-splitting, but the ambiguous effect of oxygen vacancies severely restricts the device performance. We show that electron trapping by oxygen vacancies in BiVO4 strongly depends on the operational conditions of the PEC. Under low applied bias, trapping can take up to a hundred microseconds followed by recombination on the millisecond timescale. Band bending induced by higher bias leads to the depletion of the electrons in trap states, thereby reducing the trapping lifetime. These studies are an important step towards the understanding of oxygen vacancies and the effect on the performance of BiVO4 photoanodes for water splitting, and could be used to guide the design of more efficient photocatalysts.

Resume : Engineered materials and devices typically involve interfaces of various forms that introduce property modifications of interfaced materials by introduction of stresses and strains. In this study, we focus on interfaces created in silicon associated with inhomogeneous stresses and specifically address their strong effect on radiative properties of indirect bandgaps. In particular, attention is drawn to the sol-gel based dielectric coatings on silicon that modulating the indirect bandgap of Si favorably towards radiative recombination of free-carriers. Photoluminescence and stresses levels properties of surface engineered interfaces via colloidal coatings is compared to those of thermal and chemical deposited coatings. Appreciable improvements of band edge light emission is presented. Other techniques and structures of similar random interfacial stresses and expected efficient radiative recombination properties will be presented.

Resume : The use of nanodimensional materials in advanced heterostructure-based electron devices allows us to gain a deeper knowledge about the concentration of impurity atoms on the surface and their depth distribution. In this study, we for the first time, report experimental data on the influence of O2+ ion implantation on the surface composition and depth distribution of atoms in the Si/Cu(100) system. Next, samples were transferred to a general-purpose ultrahigh-vacuum experimental setup, where ion implantation, heating, and all studies were performed at a pressure of 10–6 Pa. The surface structure and composition were examined by Auger electron spectroscopy (AES) and low-energy electron diffraction (LEED). The SiO2 films were found to be amorphous. The energy band parameters were estimated from photoelectron spectra. Before implantation, Si/Cu samples were degassed at T = 700–750 K for 2–3 h in ultrahigh vacuum (P ≤ 10–5 Pa). AES data showed that upon heating, the oxygen and carbon concentrations on the silicon surface equal 4–5 and 2 at %, respectively. At the Si–Cu interface, a transition Cu2Si3 silicide layer 8–10 nm thickarises. Implantation of 1-keV O2+ ions was carried out at saturation dose D ≈ Dsat ≈ 6 × 1016 cm–2. Analyzing the full Auger spectrum, we see that the surface contains oxides, such as SiO, SiO2, and Si2O, and extra Si and O atoms. The total concentration of silicon is within 45–50 at %, and that of oxygen lies in the interval 50–55 at %. After heating to 700 K, the peak at 76 eV, which is typical of SiO2, sharply grows, whereas others decline to a minimum. Calculations showed that the surface concentrations of SiO2, Si, and nonstoichiometric oxides in this case equal 90–92, 5–6, and 5–7 at %, respectively. Annealing of thick SiO2 films at 850–900 K makes them impurity-free and homogeneous. In the case of free thin films, dopant atoms start evaporating from them at 750 K, so that it is basically impossible to obtain impurity-free SiO2 films with a high stoichiometry. SiO2 nanofilms 1.5- to 2.0-nm-thick can be synthesized by implantation of O2+ions into a free Si/Cu system with subsequent annealing. The synthesized film contains a large amount of unbound Si atoms (5–6 at %) and nonstoichiometric oxides. They decrease the energy gap of SiO2 more than two fold.

Resume : Stringent requirements to increase device performance and reduce power consumption, while maintaining a good manufacturability and yield performance without penalizing the cost/function, are driving microelectronic research towards sub 10-nm technologies. Advanced device structures like FinFETs, TFETs, Gate-All-Around (GAA), horizontal and vertical nanowires (NWs) and nanosheets (NSs) are extensively investigated for both logic and analog/RF building blocks enabling System-on-Chip (SoC) applications. A 3-nm GAA horizontal Multi-Bridge-Channel MOSFETs has been reported as an efficient building block for high-density SRAM circuits. There is also strong interest in the implementation of 2D materials. Heterogenous integration of Ge and III-V technologies on a silicon platform has a strong potential, leading towards the on-chip integration of building blocks with different functionality. Also wide bandgap materials such as GaN are offering unique features for RF applications used in base stations for mobile communication, complementing the performance of Si devices suffering from limited output power. These materials can epitaxially be grown on 200- or 300-mm Si substrates, although the main challenge related to hetero epitaxy of III-V materials remains the control of extended defects due to the lattice mismatch of the different materials. This paper reviews trends in advanced Si(Ge) and III-V technologies on a silicon platform, focusing on the main technological challenges.

Resume : Intensive research interest has observed in the development of Transition Metal Oxides (TMOs) for the wide verities of applications. However, to activate these materials at low temperature become a critical bottleneck to their widespread implementation and compatible with flexible polymer substrates. Low temperature activation can be implemented by changing the cation composition and oxygen vacancy concentration. In this report, we firstly demonstrated and standardized highly controllable activation of several TMO by this unique route at very low temperatures. Here we used four different systems of TMO as sputtered IWO, IZO, In2O3, IGZO, and solution processed IZO. The tuning of oxygen stoichiometry of AMOS has been carried out by using a tetramethyl aluminum (TMA) precursor treatment right after the device fabrication process. Typically, Al has low standard reduction potential E°Al3+/Al = −1.662 V and smaller atomic size, which enable a stronger bonding between the abundant oxygen atoms inside the AMOS. At the same time, Al atom is also capable of pulling off some of the weakly bonded oxygen atoms from the non-perfect M-O bonds and forms Al-O bonds. This process leads to a decrease of weakly bonded oxygen density inside the film results activation of the TMO systems at low temperatures. The detailed electrical parameter analyses and in-depth study of stochiometric transformations, monitored via spectroscopic measurements (X-ray photoelectron spectroscopy) provide critical insights into the underlying oxygen-vacancy generation mechanism. Demonstration of low temperature activation promises alternative to conventional high temperature annealing strategies, facilitating facile fabrication of multifunctional electronic circuits and neuromorphic transistors for bioinspired computing. Key Words: Transparent amorphous oxide semiconductor (TAOS), Thin films, Indium Tungsten Oxide, Indium oxide, Indium Zinc Oxide, Flexible thin films transistor, Synaptic transistor.

Resume : In response to the coming of 5G and the Internet of Things generation, the demand for non-volatile memory has dramatically increased. Bipolar non-volatile memory was demonstrated in Al/MgInO/ITO structure on glass substrate. The MgInO film of 30 nm was deposited on ITO by RF magnetron sputtering in Ar ambient at room temperature. The MgInO thin film was annealed in vacuum ambient at 300 °C for 30 min. The device has lager memory window about 103 between low resistance state and high resistance state. The memory also show small switching voltage which set and reset voltage is -0.91V and 0.6V, respectively. To analyze the current conduction mechanism in memory. In the high resistance state, the current conduction mechanism is a linear relationship between the root voltage and the natural log of the current, indicating that it conforms to the Schottky emission mechanism. In the low-resistance state, the current-voltage is a simple positive correlation ohmic conduction mechanism, which represents the filament theory. Furthermore, switching between low resistance state and high resistance state can work 500 times. In this study, the device has great performance of memory characteristic.

Resume : This talk will focus to introduce a new type of optoelectronics based on nanomaterials, such as small band gap colloidal quantum dots and wide band gap nanoparticles of oxide semiconductor. Highly transparent phototransistors and photodiodes, which can absorb visible-light and generate electrical signal, have been fabricated with a heterostructure comprised of an small band gap CdSe quantum dots and a wide band gap ZnO. During the presentation, the interfacial electronic structure of the heterostructure will be considered as well as the fabrication process of the device. The measurements and analysis of the interfacial physics and the photoexcited charge transfer mechanism at the device will be introduced in detail using time-resolved photoluminescence spectroscopy, scanning Kelvin probe microscopy and x-ray/ultraviolet photoelectron spectroscopy. In addition, a method to fabricated highly transparent photosensors, which can be perfectly turned on and off by a low-energy visible light based on quantum-dots and metal nanoparticles will be discussed. In this way, highly transparent NOT, NOR, and NAND optical logic circuits were fabricated as well as the optical image sensors. These kinds of optoelectronics are considered as an emerging science and technology due to the potential applications including transparent and soft interactive devices.

Resume : The past several years have witnessed heightened interest in metal halide perovskite (MHP) materials as promising active candidates for optoelectronic applications. Particularly, the intensive research of MHP‐based solar cells, photodetectors, and light‐emitting diodes could probably reform the optoelectronic semiconductor industry. In comparison, in spite of the large intrinsic charge carrier mobility of MHPs, the development of MHP‐based field‐effect transistors (MHP‐FETs) is relatively slow, but also potentially rewarding. We reported that the solution-processed MHPs, including the various forms of thin films, single crystals, and the relevant composites, can be used to develop the high-performance transistors that shows great potential in the applications of large-area electronics and light-sensing devices. Herein, I will present that the phototransistors based on MHP thin films can be realized upon employing light illumination, that exhibit clear ambipolar charge transport properties and high photo-response characteristics. Moreover, the spatially-confined inverse temperature crystallization technology was employed to grow the micrometer-thin MHP crystals, from which the transistors showed high carrier mobility and On-Off ratio. We also demonstrated that the transistor device performance can be enhanced significantly through coupling MHPs with low-dimensional materials.

Resume : We predict that conduction electrons in a semiconductor film containing a centered square array of metal nanowires normal to its plane are bound in quantum states around the central wires, if a positive bias voltage is applied between the wires at the square vertices and these latter. We obtain and discuss the eigenenergies and eigenfunctions of two models with different dimensions. The results show that the eigenstates can be grouped into different shells. The energy differences between the shells is typically a few tens of meV, which corresponds to frequencies of emitted or absorbed photons in a range of 3 THz to 20 THz approximately. These energy differences strongly depend on the bias voltage. We calculate the linear response of individual electrons on the ground level of our models to large-wavelength electromagnetic waves whose electric field is in the plane of the semiconductor film. The computed oscillator strengths are dominated by the transitions to the states in each shell whose wave function has a single radial node line normal to the wave electric field. We include the effect of the image charge induced on the central metal wires and show that it modifies the oscillator strengths so that their sum deviates from the value given by the Thomas-Reiche-Kuhn rule. We report the linear response, or polarizability, versus photon energy, of the studied models and their absorption spectra. These latter show well-defined peaks as expected from the study of the oscillator strengths. We show that the position of these absorption peaks is strongly dependent on the bias voltage so that the frequency of photon absorption or emission in the systems described here is easily tunable. This makes them good candidates for the development of novel infrared devices.

Resume : First-principles full-potential linearized augmented plane-wave method based on density functional theory is used to investigate the structural, electronic, thermoelectric and thermodynamic properties of the cubic Rattling Heusler (RH) Ba2AuZ (where Z= Bi, Sb ),within the local density approximation (LDA) and generalized gradient approximation (GGA) for potential exchange correlation. The modified Becke-Johnson (mBJ) potential approximation is also used for calculating the electronic band structure and density of states of the full-Heusler compounds Ba2AuSb and Ba2AuBi. We have analyzed the structural parameters, total and partial densities of states (TDOS and PDOS). The results show that the electronic property of this cubic Rattling Heusler has a semiconductor behavior with indirect band gap using GGA-PBE and mBJ-GGA approximations. The very important value of the merit factor (ZT) and Seebeck coefficient(S) make it a promising candidate for thermoelectric applications. Keyword: Semiconductor behavior; Rattling Heusler; Seebeck coefficient; Thermoelectric applications.

Resume : CMOS single photon avalanche diode (SPAD) detectors are used in many applications below 1000 nm wavelength including mobile phones, autonomous vacuum cleaners, biological imaging, quantum imaging and light detection and ranging (LIDAR). Telecomm applications require 1310 or 1550 nm wavelengths and there are significant benefits to LIDAR at longer wavelength due to reduced solar blindness, higher eye safe laser powers and improved atmospheric transparency. We present Ge-on-Si SPADs operating at 1310 nm wavelengths with single photon detection efficiencies up to 38% at 125 K. The devices demonstrate Geiger mode single photon detection up to 200 K and high efficiencies up to 1500 nm. Measurements of afterpulsing using nominally identical parameters on both Ge-on-Si and InGaAs SPADs demonstrate the Ge-on-Si devices to have a 5 times lower afterpulsing probability which is key for quantum communication and LIDAR applications. We demonstrate LIDAR using a single pixel Ge-on-Si SPADs at 1450 nm with mechanical raster scanning, 100 kHz laser repetition rates and time-correlated single-photon counting techniques with a range of reconstruction algorithms to demonstrate amplitude and depth imaging in laboratory conditions. The results were used to predict that such LIDAR systems could be used for up to 1 km range with eye-safe powers using integration times of 10 ms or more per pixel. The use of these detectors for LIDAR and quantum communications will be reviewed and discussed.

Resume : Near infrared (NIR) imaging technology has been getting a lot of attraction not only in traditional but also emerging application such as IoT sensor, night vision for autonomous vehicle, security/surveillance camera, and facial recognition. In the present study we report both efficient and harmless, from the point of view of fabrication process, silicon NIR sensor by adopting thin random nanopatterns of gold. Although gold is not only strictly prohibited in silicon process but also light reflecting material for most electromagnetic wave, the present sensors show enhanced absorption of NIR due to the thin gold nanopattern. We implemented p-i-n photodetectors on p-type (100) Si where the light absorbing layer of 0.8 micrometer is epitaxially grown and followed by the fabrication of c.a. 10 nm-thick random gold film. Under irradiation of 980 nm NIR the present photodetectors show very high photosensitivity of 0.4 A/W which is tens of times larger than that of the same device without gold pattern. We also quantitatively analyzed the enhancement in terms of quantum efficiency and specific detectivity (D*). As a result, we noted that the presence of thin gold nanopattern is substantially and positively influential on the NIR photosensitivity of silicon photodetector in spite of the absence of either periodicity or regularity of the pattern. We will address furthermore on the enhanced photoelectric characteristics of gold nanopattern using the results of finite EM simulation.

Resume : The dielectric spectroscopy is a powerful tool in determining the electrical properties of the different inorganic materials. Recently, many studies were focused on the dielectric properties and charge carrier transport in ferrites. The influence of doping of the oxides on the dielectric permittivity and other factors, such as dielectric losses were studied in the details. Generally, in the magnetite nanoparticles (Fe3O4 NPs), three different processes can occur, depending on the temperature and frequency range. The first one, observed for ultrahigh frequencies, is related to the vibration of ions in the crystal structure and defects polarization. Two others are related to the charge carriers' generation and their movement. In the performed studies, it was stated, that the introduction of different organic molecules on the surface of nanoparticles can change the charge carrier transport by the grain boundaries, especially by stabilization of Fe2 or Fe3 ions. Moreover, the passivation of the surface of Fe3O4 NPs and the formation of the Fe2O3 layer can be monitored using dielectric spectroscopy by analysis of the imaginary part of the electric modulus. Additionally, the modification of the shape and size of magnetite nanoparticles can be also used to change the dielectric properties, especially electrical conductivity. According to that, it is possible to modify the properties of magnetite nanoparticles and synthesize insulators or semiconductors from the same compound.

Resume : Presently, silicon photonics requires photodetectors that are sensitive in a broad infrared range, can operate at room temperature, and are suitable for integration with the existing Si-technology process. Here, we demonstrate strong room-temperature sub-band-gap photoresponse of photodiodes based on Si hyperdoped with tellurium. The epitaxially recrystallized Te-hyperdoped Si layers are developed by ion implantation combined with pulsed-laser melting and incorporate Te-dopant concentrations several orders of magnitude above the solid solubility limit. With increasing Te concentration, the Te-hyperdoped layer changes from insulating to quasi-metallic behavior with a finite conductivity as the temperature tends to zero. The optical absorptance is found to increase monotonically with increasing Te concentration and extends well into the mid-infrared range. Temperature-dependent optoelectronic photoresponse unambiguously demonstrates that the extended infrared photoresponsivity from Te-hyperdoped Si p-n photodiodes is mediated by a Te intermediate band within the upper half of the Si band gap. This work contributes to pave the way toward establishing a Si-based broadband infrared photonic system operating at room temperature. The work has been published at Phys. Rev. Applied 10, 024054 (2018).

Resume : The recent rise of semiconductor nanowires opens new opportunities due to the unique one-dimensional structure with remarkable electrical and optical properties. Silicon nanowires (Si NWs) represent one of the most promising resources to be employed in modern nanodevices. We demonstrated the realization of a dense array of vertically aligned Si NWs with tunable aspect ratio by a low-cost, mask-less approach compatible with the Si technology. Si NWs with an efficient room temperature (RT) light emission would represent a great industrial advancement, opening the route to a wide range of unexpected photonic applications. In this work, we will demonstrate that it is possible to realize a new hybrid material based on luminescence with Si NWs and different dyes (Ru4, Ru3Os) for light harvesting antenna applications, without any functionalization and with efficiencies of the order of 95%. These hybrid light-harvesting antennas are very promising for different applications in the bio-imaging, sensors, photonics and energy fields. When a dye is introduced in these NWs a strong NW-dye interaction sets in and the energy is preferentially transferred from the NW to the dye. These hybrid materials based on NWs provide the great advantages of compatibility with silicon technology, low cost, stability and high photoinduced energy transfer efficiency.

Resume : In this study, we report a novel 0D/2D photocatalyst (MXene-g-C3N4), which is comprised of MXene quantum dots and ultrathin g-C3N4 nanosheets. It exhibites highly enhanced photoresponse and excellent photocatalytic performance toward the degradation of Tetracycline (TC). Detailed characterization reveals that MXene QDs (≈4.9±6.2 nm) are tightly attached on the surface of g-C3N4 nanosheets. The content of 3.0 wt% of MXene QDs resulted in a 19.1-fold higher reaction rate than that of pure g-C3N4 under visible light irradiation. The improved photocatalytic performance can be attributed to the strong interfacial interaction between MXene QDs and g-C3N4 nanosheets and larger surface area. The reactive species scavenging experiments display that that the h+, ∙OH, and O2∙− are dominant active species for TC removal. Finally, a possible Z-scheme photocatalytic mechanism of MXene-g-C3N4 composites was proposed.

Resume : The Cu2O-based photocathode is considered as one of the best performing photocathode materials for solar water reduction. However, the relatively negative onset potential for H2 production of these photocathodes impedes further optimization of the solar-to-fuel conversion efficiency. An important reason is the inability to achieve meaningful photovoltages with Cu2O. Here, the photovoltage barrier can be readily broken by replacing the semiconductor/water interface with a semiconductor/semiconductor one. A n-Cu2O layer was found to form high-quality buried junction with p-Cu2O to increase the photovoltage and thus shift the turn-on voltage positively. Mott−Schottky Measurements confirmed that the improvement was benefited from a thermodynamic shift of the flatband potentials. An extremely positive onset potential in n-Cu2O/AuAg/p-Cu2O was further obtained, which is comparable to what has been measured using water reduction catalysts. The alloy nanoparticles sandwiched between the homojunction of n-Cu2O and p-Cu2O play an important role in enhancing the photocatalytic performance. First, the alloy nanoparticles not only serve as an electron relay, but also promote electron-hole pair generation in nearby semiconductors, which facilitates the charge transfer between n-Cu2O and p-Cu2O since the sandwich structure is measured by X-ray absorption spectroscopy. Second, the alloy nanoparticles act as a plasmonic photosensitizer, which enables the solar-to-hydrogen conversion at wavelengths longer than the band edge of homojunction structure, extending the incident photo-to-current conversion efficiency wavelength. Finally, the plasmonic energy-transfer mechanism is identified as direct transfer of the plasmonic hot carriers, and the interfacial Schottky barrier height is shown to modulate the plasmonic hot electron transfer. This facile sandwich structure combines both the electrical and the optical functions of alloy nanoparticles into a single structure, which has implications for the design of efficient solar-energy-harvesting devices.

Resume : Highly doped super steep shallow juntion is required not only by the integration of CMOS devices, it’s also essential for the fabriction of advanced photo detectors. As has been reported, to achieve a defect free PN junction with higher activation level, both insitu-doping and ion implantation are prefered as the cutting edge doping technologies, however ion implantation is more convenient when performing a selective doping process, what’s more, an optimized annealing process such as microwave annealing is still need to activate the dopants and eliminate the defects induced by implantation. In this work, B18H22 was used as cluster ions to perform P type doping on a silicon substrate, for a better charactering , the substrate was first lightly doped by Phosphours to form a n-well from the surface to the depth of about 2um, and the concentration of is kept at 1x1018cm3. The activation process was completed by using microwaver annealing system at varied power in N2 ambinent. And spike annealing is also used to make comparision with MWA (microwave annealing). Hall measurement ellipsometry Sims and TEM were adoped to characterize the performance of the junction. Microwave annealing is proved to be a promising solution to activate the dopant and repair the defect induced by implantaion at a relative low temperature which is meanful for the controling of the jucntion depth.

Resume : The transistor design moves toward vertically or laterally stacked Gate-All-Around (GAA) where Si or SiGe can be used as channel material. Epitaxial Si / SiGe superlattice stacking, and precise and selective etching of a material to obtain nanowire or nanosheet structure has become a very critical technology. In this study, an innovative SiGe dry selective selective etching method was proposed. It mainly discusses how to obtain the self-limiting atomic layer etching process. A film layer structure was grown on a 200 mm diameter silicon wafer by an epitaxial process as Si-sub / 10nm Si / 10nm SiGe / 10nm Si / 10nm SiGe / 10nm Si / 10nm SiGe / 10nm Si. Then a side wall transfer method is used to obtain a hard mask with a width of less than 40 nm, and then the stack is opened by HBr / O2 / He plasma anisotropic etching and steep etching. Then, the isotropic selective etching process is studied. The ICP etching machine with time-etching function is used as the research object. And compare the results of wet and other etching. Finally, a nanosheet structure of about 10 nm is obtained. The main goal of this research is to provide a new manufacturing method for obtaining accurate nanowire / sheet structure. In the field of horizontal or vertical ring gate device manufacturing, the new nano-sensor field has very important application value. The film stacks and structure after etching were characterized by high-resolution scanning electron microscope (HRSEM), Secondary ion mass spectrometry (SIMS), high-resolution transmission electron microscopy (HRTEM), Hall measurement, and high-resolution x-ray diffraction techniques (HRXRD). Acknowledgement This work was financially supported by the science and technology planning project of Beijing (Z191100010618005), the National Key Project of Science and Technology of China (Grant No. 2017ZX02315001-002) and the National Key Research and Development Program of China (Grant No. 2016YFA0301701), which are acknowledged. References [1]XiaogenYin., Yongkui Zhang., HuilongZhu(2020).Vertical Sandwich Gate-All-Around Field-Effect Transistors with Self-Aligned High-k Metal Gatesand Small Effective-Gate-Length Variation.IEEE ELECTR DEVICE L,41(1),8-11 [2] Junjie Li.,Wenwu Wang.,Yongliang Li(2019).Study of selective isotropic etching Si1−xGex in process of nanowiretransistors.J MATER SCI-MATER EL. 2019(10.5 pubished online)

Resume : Studies on Growth and Integration of SiGe/Ge layers as Channel Materials in Advanced Transistors Yan Dong1, Guilei Wang1*, Jun Luo1, Zhenzhen Kong1, Jiniao Liu1, Junjie Li1, Tao Yang1, Junfeng Li1, Huaxiang Yin1, Chao Zhao1, Wenwu Wang, Tianchun Ye1, and Henry H. Radamson2 1Key Laboratory of Microelectronics Devices & Integrated Technology, Institute of Microelectronics of Chinese Academy of Sciences, Beijing, 10029, China 2 Department of Electronics Design, Mid Sweden University, Holmgatan 10, 85170 Sundsvall, Sweden *wangguilei@ime.ac.cn As CMOS technology downscaled into 22nm a transition from 2D to 3D transistors took place and a revolutionary FinFET design was introduced. During this R&D, different strain engineering methods containing selectively growth of SiGe on source/drain as stressor material was used to increase the channel mobility [1]. Another way to handle the channel mobility issue is to integrate Ge material which has high mobility for both p and n channel instead of having Si fin in the transistor structure. In this study, the Si Fin is processed and later removed to make the trench between the STI SiO2 and a SiGe/Ge bilayer, which is selectively grown to fill the trench that is used as the MOS channel. In principle, there are two methods to remove the Si Fins. One is using the WET etch, the another one is using and the HCl etch during the epitaxy process. Since SiGe/Ge epitaxy process is sensitive to the surface quality of the Si Fin then a careful in-situ cleaning is needed to remove all undesired residuals from the Si surface. The Ge content and the strain amount in the SiGe layers was directly measured by using high-resolution x-ray diffraction (HRXRD) rocking curves (RC). RCs were done at (113) reflection where the incident beam is as low as 2.6° and a large area of sample containing a variety of transistors could be within the coverage of the x-ray beam. These RCs were simulated by the Takagi-Taupin equations and compared to the experimental curves in order to obtain highly accurate data for analysis. Cross-section images were provided by high-resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (HRTEM) to measure the layer thickness, epi-quality, and integrity of the whole transistor structures. In the latter analysis, energy dispersive spectroscopy (EDS) technique was also applied to reconfirm the Ge profile in the channel regions of the FinFETs. References [1] Wang G, Abedin A, Moeen M, et al. Integration of highly-strained SiGe materials in 14nm and beyond nodes FinFET technology[J]. Solid-State Electronics, 2015, 103: 222-228. [2] Henry H. Radamson, Yanbo Zhang, Xiaobin He, Hushan Cui, Junjie Li, Jinjuan Xiang, Jinbiao Liu, Shihai Gu, Guilei Wang: The challenges of advanced CMOS process from 2D to 3D. Applied Sciences 10/2017; 7(10):1047. [3] Henry H. Radamson, Xiaobin He, Qingzhu Zhang, Jinbiao Liu, Hushan Cui, Jinjuan Xiang, Zhenzhen Kong, Wenjuan Xiong, Junjie Li, Jianfeng Gao, Hong Yang, Shihai Gu, Xuewei Zhao, Yong Du, Jiahan Yu, Guilei Wang: Miniaturization of CMOS. Micromachines 04/2019; 10(5):293., DOI:10.3390/mi10050293

Resume : The high aspect ratio of Si nanowire (NW) arrays has a great potential for many applications and in particular for Si-based sensors. For this purpose, we coupled the huge surface-to-volume ratio of Si NW to plasmonic effects decorating the NW array with metal nanoparticles (NPs). Si NWs were synthesized by metal-assisted chemical etching and then decorated with silver nanoparticles (NPs) produced by pulsed laser deposition (PLD). Both NW synthesis and decoration techniques are performed at room temperature with a low-cost and Si implementable technology. The obtained Ag NP decorated Si NWs are free from chemicals contamination and there is no need of post deposition high temperature processes. The results show that this approach allows the full coverage of the Si NW walls with a strong control on the Ag NP size and distribution. The optical properties of Si NW arrays were investigated by reflectance spectroscopy showing the presence of a plasmon absorption peak dependent on the Ag NP morphology. The great potentialities of PLD metal decoration of Si NWs for surface enhanced Raman spectroscopy (SERS) applications are reported as a function of rhodamine 6G (R6G) concentration in aqueous solution. A very low limit of detection of 10−8 M was demonstrated and a SERS enhancement factor of 108 of about one order of magnitude higher with respect to a similarly decorated Si flat surface was estimated.

Resume : n this paper, we report on the realization of a highly sensitive and low cost 3D surface-enhanced Raman scattering (SERS) platform. The structural features of the Ag dendrite network that characterize the SERS material were exploited, attesting a remarked self-similarity and scale invariance over a broad range of length scales that are typical of fractal systems. Additional structural and optical investigations confirmed the purity of the metal network, which was characterized by low oxygen contamination and by broad optical resonances introduced by the fractal behavior. The SERS performances of the 3D fractal Ag dendrites were tested for the detection of lysozyme as probe molecule, attesting an enhancement factor of ~2.4 × 106. Experimental results assessed the dendrite material as a suitable SERS detection platform for biomolecules investigations in hydration conditions

Resume : In this paper, we present the realization by a low cost approach compatible with silicon technology of new nanostructures, characterized by the presence of different materials, such as copper iodide (CuI) and silicon nanowires (Si NWs). Silicon is the principal material of the microelectronics field for its low cost, easy manufacturing and market stability. In particular, Si NWs emerged in the literature as the key materials for modern nanodevices. Copper iodide is a direct wide bandgap p-type semiconductor used for several applications as a transparent hole conducting layers for dye-sensitized solar cells, light emitting diodes and for environmental purification. We demonstrated the preparation of a solid system in which Si NWs are embedded in CuI material and the structural, electrical and optical characterization is presented. These new combined Si NWs/CuI systems have strong potentiality to obtain new nanostructures characterized by different doping, that is strategic for the possibility to realize p-n junction device. Moreover, the combination of these different materials opens the route to obtain multifunction devices characterized by promising absorption, light emission, and electrical conduction.

Resume : Gate-all-around (GAA) FETs are considered the potential candidates to replaced FinFETs for advanced integrated circuit manufacturing technology at/beyond 3 nm technology node. Vertical GAAFETs have free design flexibility on gate length and have great potential to increase integrated density. A multilayer (ML) of Si/SiGe/Si is commonly grown to form vertical transistors where the vertical GAAFETs are formed by a vertical etch followed by a lateral etch. In the latter process, the SiGe layer is selectively etched to create the channel layer. The Si layers are source/drain and are often P-doped for nFETs. The segregation, auto-doping and out-diffusion problems of P-doped Si/SiGe interface have not been solved and they are crucial for the fabrication of vertical nanowire devices. In this study, we discussed the segregation, auto-doping and out-diffusion phenomenon in P-doped Si and intrinsic SiGe MLs. The layers were epitaxially grown by reduced pressure chemical vapor deposition system (RPCVD), using SiH4 and GeH4 as precursors. Different strategies e.g. hydrogen-purge during epi, and/or inserting a sacrificial intrinsic Si layer after P-doped Si, substituting SiH4 by SiH2Cl2 (DCS) and varying the growth temperature and total pressure in epi-reactor were proposed to solve the epitaxy problems. Experiments showed that the segregation and auto-doping could also be relieved by adding 5% Ge to P-doped Si. The layer and interface quality were studied in these samples. The selective etching between n Si (or n Si0.95Ge0.05) and Si0.78Ge0.22 was also discussed by using wet and dry etchings. The main goals of this study were to manufacture n Si/SiGe/n Si MLs structures and optimizing selective etching between n Si and SiGe with high repeatability for vertical GAAFETs. The Si/SiGe/Si MLs were characterized by the techniques of High-Resolution Transmission Electron Microscopy (HRTEM), High-Resolution X-Ray Diffraction (HRXRD), Scanning Electron Microscopy (SEM), and Secondary Ion Mass Spectroscopy (SIMS).

Resume : In this work, we investigated the composition of the MoO_3 nanofilms, the energy band parameters, and the velocity of valence electrons by implanting oxygen ions. As a target we received single crystalline Mo (111) with a diameter of 10 mm and a thickness of 0.3 mm.Before ion implantation, we heated the target at vacuum (P = 10^(-6) Pa)T = 2000 K for 25-30 hand heated the pulse T = 2200K. Apply oxygen vacuum chamber to P = 10^(-2) Pa Pa in special gas bubble. We change the ion energy at 1-5keV and the dose at 4-8∙ 10^17 sm. In order to improve the stoichiometric composition of the MoO_3nanoparticle, we heat it at T = 850 K during ion implantation because this temperature is the optimum temperature and allows uniform thin films on the surface.During ion implantation, we made films of different thicknesses, such as 30Å, 60Å, and 90Å thickness. The composition, electron structure and physical properties of nanofilms were studied by means of Oje - electron spectroscopy, electron spectroscopy, which lost characteristic of photoelectron spectroscopy. The stoichiometric composition of the nanofilm obtained during thermal oxidation is slightly homogeneous, with a transition layer width of 65-70 Å. The content of the MoO_3 nanoparticle obtained by ion implantation remained unchanged at 60 Å and the width of the transition layer did not exceed 40-45 Å

Resume : The Ba0.95Ca0.05Ti0.92Sn0.07Zr0.01O3 sample was prepared by solid- solid method. The structural, morphologic and dielectric properties were studied. In addition to the experimental study, theoretical approaches were adopted to investigate electrocaloric behavior of this sample. The electrocaloric entropy changes, heat capacity changes, and temperature changes as a function of temperature under different electric field shifts. The important parameters such as Maximum entropy change, relative cooling, and refrigerant capacity were explained qualitatively. From the hysteresis cycles, our studied sample showed a typical ferroelectric behavior with a low coercive field. These results make our sample promising candidate for the development of refrigeration device and evaluation of its efficiency.

Resume : Nanostructured materials have been extensively studied during the last years due to their great variety of potential applications. In particular, chemical sensors based on semiconducting monolayers, such as silicene, have been proposed [1, 2]. Theoretical investigations indicate that the semiconducting tin carbide (SnC) monolayer is stable [3-5] and the addition of impurities, such as B, Al and N, can modify not only the electronic properties of SnC nanoribbons but also their magnetic behavior [6]. Moreover, other theoretical studies suggest that SnC nanotubes could detect harmful gases such as SO2, H2CO, and NH3 [7]. In this work, we theoretically address the capability of SnC monolayers as molecular sensors to detect CO, CO2, NO, SO2, and HCN molecules, by using density functional calculations. The results show that CO and NO are adsorbed on both Sn and C atoms with adsorption energies larger close to 1 eV indicating that these molecules are chemically adsorbed onto the SnC nanosheet. Also, the electronic structures of the formed complexes are discussed. This work was supported by UNAM-PAPIIT IN109320. Computations were performed at the supercomputer Miztli of DGTIC-UNAM (Project LANCAD-UNAM-DGTIC-180). A.L.M.V. would like to thank CONACYT and BEIFI-IPN for her scholarship. References [1] J Prasongkit, RG Amorim, S Chakraborty, et al., J. Phys. Chem. C 119, 16934-16940 (2015). [2] T Hussain, T Kaewmaraya, S Chakraborty, et al., ACS Sens. 3, 867-874 (2018). [3] H. Şahin, S. Cahangirov, M. Topsakal, E. Bekaroglu, E. Akturk, R. T. Senger, S. Ciraci, Phys. Rev. B 80, 155453 (2009). [4] T.-Y. Lü, X.-X. Liao, H.-Q. Wang, J.-C. Zheng, J. Mater. Chem. 22, 10062 (2012). [5] Y. Mogulkoc, M. Modarresi, A. Mogulkoc, Y.O. Ciftci, B. Alkan, J. Chem. Phys. Solids 111, 458 (2017). [6] H. Ghaziasadi, P. Nayebi, Mater. Res. Express 5, 115012 (2018). [7] P. N. Samanta, K. K. Das. Int. J. Quantum Chem. 116, 411–420 (2016).

Resume : The La0.8Ba0.1Ca0.1Mn0.8Co0.2O3 sample was prepared by polymerization complex sol-gel method. The structural and electrical properties were studied. The sample crystallizes in the orthorhombic structure with Pbnm space group. In addition to the structural study, theoretical approaches were adopted to investigate the electrical behavior of this sample, showing the semiconductor behavior in all temperatures. This can be explained by small polaron hopping and Mott's variable range hopping

Resume : Inverse Heusler alloys possessing spin gapless semiconducting behavior have drawn great curiosity among researchers in the past few months on account of their unique transport characteristics that can be put into use in spin based electronic device implementations. Thin films of a possible ternary spin gapless semiconductor Mn2CoSi (MCS) inverse Heusler alloy have been deposited on a p-Si (100) substrate using the electron beam physical vapor deposition technique. The as-grown films exhibit a polycrystalline nature having a uniform and smooth surface with full coverage. A magnetic study reveals that the film is ferromagnetically soft along the direction parallel to its plane and its Curie temperature (TC) is much higher than room temperature (300 K). The formation of the MCS/SiO2/p-Si heterostructure is confirmed from cross-sectional transmission electron microscopy and cross-sectional scanning electron microscopy studies. The electronic- and magneto- transport properties of the heterostructure have been studied at various isothermal conditions. From current–voltage characteristics, a conventional magnetic diode like behavior has been observed throughout the working temperature regime of 78–300 K. The temperature coefficient of resistance (TCR) value of the film is estimated to be –2.09 × 10−9 Ω m/K, which is similar to the TCR values of reported spin gapless semiconductors. Room temperature spin injection and detection in a nonmagnetic semiconductor (p-Si) has been carried out using the three-terminal Hanle device in our MCS/SiO2/p-Si heterostructure. The estimated values of spin lifetime (78 ps) and spin diffusion length (167 nm) of the injected carriers at room temperature provide an indication of their industrial importance in future spin based electronic device applications.

Resume : Heterostructures of two-dimensional (2D) materials represent a powerful material platform that has essentially defined the technological foundation for all modern electronic and optoelectronic devices. Although most of the reported heterostructures devices exhibit extraordinary electronic and optoelectronic properties, it depends on the proper combination of selected materials, which limits the broad tunability of the devices. Here, we demonstrate a vertical van der Waals heterostructures (vdWHs) device, which is composed of MoS2 and MoTe2, can function as a backward tunneling diode, photovoltaic cell and photodetector through surface functionalization of MoO3. The realization of this backward tunneling diode is attributed to the band alignment variation from type II to type III via in situ MoO3 functionalization. Furthermore, the power conversion efficiency of this vdWHs based photovoltaic device is significantly enhanced by nearly 4 times, benefiting from the more efficient photocarrier separation after MoO3 decoration. The enhanced photovoltaic effect can be retained even after air exposure, revealing the excellent air stability. Meanwhile, the modified vdWHs device exhibits the photodetecting property with photocurrent responsivity of around 2 A/W and EQE about 400%. This work promises surface functionalization as an effective approach to broaden the device functionality of 2D heterostructures in electronics and optoelectronics.

Resume : Despite many encouraging properties of transition metal dichalcogenides (TMDs), a central challenge in the realm of industrial applications based on TMD materials is to connect the large-scale synthesis and reproducible production of highly crystalline TMD materials. Here, the primary aim is to resolve simultaneously the two inversely related issues through the synthesis of MoS2(1−x)Se2x ternary alloys with customizable bichalcogen atomic (S and Se) ratio via atomic-level substitution combined with a solution-based large-area compatible approach. The relative concentration of bichalcogen atoms in the 2D alloy can be effectively modulated by altering the selenization temperature, resulting in 4 in. scale production of MoS1.62Se0.38, MoS1.37Se0.63, MoS1.15Se0.85, and MoS0.46Se1.54 alloys, as well as MoS2 and MoSe2. Comprehensive spectroscopic evaluations for vertical and lateral homogeneity in terms of heteroatom distribution in the large-scale 2D TMD alloys are implemented. Se-stimulated strain effects and a detailed mechanism for the Se substitution in the MoS2 crystal are further explored. Finally, the capability of the 2D alloy for industrial application in nanophotonic devices and hydrogen evolution reaction (HER) catalysts is validated. Substantial enhancements in the optoelectronic and HER performances of the 2D ternary alloy compared with those of its binary counterparts, including pure-phase MoS2 and MoSe2, are unambiguously achieved.

Resume : Because of the sensitivity to its environment of the atomic scale material itself, controlling environments such as substrate and interface of junction is important. Using 2D heterostructure, we can improve the performance of device and figure out the effects of environments. We are interested in transition metal phosphide(TMPS) which is one of the emerging new class of 2D van der Waals(vdW) materials. TMPS is considered as promising candidates to study synergistic effects when integrated with other 2D materials. In this research, we used CrPS4 as a gate insulator in MoS2 FET device on SiO2/Si substrate. We fabricated the FET device and performed atomic force microscopy(AFM) to confirm the surface and thickness of MoS2 and CrPS4. In our experiment, we compared I-V characteristics of the device with and without junction of CrPS4. We report the enhanced electrical performance of a MoS2 field-effect transistor (FET) by using a contact with a layered CrPS4 . Our transport measurements revealed that MoS2 channel with CrPS4 junction showed higher mobility of 33.9 cm 2 /Vs than that without CrPS4 junction on SiO2 /Si substrate. We also fabricated a MoS2 FET with a top gate insulator, CrPS4 , which showed low leakage current of 10 -11 A and high on/off ratio of 10 5. In a dual-gated FET with SiO2 bottom gate insulator and CrPS4 top gate insulator, very low sub-threshold swing of 0.70 V/dec was obtained.

Resume : Atomic layer deposition tungsten (ALD W) is the best filling metal in CMOS device with gate-last process since 22nm technology. The gate current, as the direct parameter to reliability, is one important parameter in nano-scale CMOS device. In this paper, the initial gate current and defect-induced gate current degradation of p-FinFET with different ALD W precursors (B2H6 and SiH4) are systematically studied. Compared to B2H6 precursor, the SiH4 precursor show lower initial gate current due to the larger compressive strain in channel (more than 2 times). At the same times, the gate current degradation of p-FinFET with different ALD W precursors is studied under gate current stress (-2.0V) and 1000s time. The results show the gate current degradation is induced by the defect in the HfO2 layer (high-k), including the pre-existing defect in high-k layer and generated defect. Based on the stress-induced leakage current (SILC) and secondary ion micro spectroscopy analysis (SIMS), the better defect-induced gate leakage current of device with SiH4 precursor is from the less pre-existing defect in bulk layer due to the more fluorine diffusion from top tungsten layer, and the energy level of defect in bulk layer is around near to valance band of silicon (Ev). In a word, ALD W SiH4 precursor shows less both initial and defect-induced gate current degradation.

Resume : Tin dioxide is the most known semiconducting metal oxide material used as gas sensor. However, it has been theoretically proposed that structures in the composition Sn(x 1)O(2x) should stabilize in a layered way. In fact, we have used the carbothemal reduction method to synthesize single crystalline layered Sn3O4 nanobelts, and we were able to manipulate the layers using a Dual Beam Microscope. Gas sensing properties of Sn3O4 material was performed by constructing a sensor device on interdigitated platinum electrodes and monitoring the electrical behavior of devices after exposing them to oxidizing (NO2) and reducing (H2, CO, CH4) gases. Results showed that best device response was to the NO2, presenting better results than the traditional SnO2 material. To support the experimental results we made Density Functional Theory (DFT) calculations about the molecules adsorption on the (010) planes of Sn3O4, which is the belt largest face experimentally obtained. PBE formulation for the exchange correlation energy functional was used in our DFT calculations, and to improve the description of the vdW interactions, we considered the DFT-D3 pairwise potential interaction functional as implemented in the VASP Package. Results showed that NO2 molecule has a strong interaction with the (010) plane of Sn3O4, presenting an adsorption energy of -524.87 meV, the largest between the studied molecules. Theoretical results are in good agreement with the experimental ones, and show that interaction of NO2 with Sn3O4 surface occurs by the interaction of tin atoms from crystal with oxygen atoms from the analyte. These studies are important in the gas sensing field since we can predict by theoretical studies which materials can have best sensor performance for a selected analyte.

Resume : Molybdenum disulfide (MoS2) opens up new possibilities for 2D electronic devices in terms of applications for low standby and low operating power electronics coupled with further miniaturization beyond Moore’s Law. Unfortunately, previous synthetic approaches appear to be technically hampered for practical applications due to their inability to obtain large-area and continuous MoS2 layers. Here, a facile methodology for the large-scale production of layer-controlled MoS2 layers on an inexpensive substrate involving a simple coating of single source precursor with subsequent roll-to-roll-based thermal decomposition was developed. The resulting 50 cm-long MoS2 layers synthesized on Ni foils possessed excellent long-range uniformity and optimum stoichiometry. Moreover, this methodology was promising because it enables simple control of the number of MoS2 layers by simply adjusting the concentration of (NH4)2MoS4. For actual industrial applications, not only a method for large-scale production but also an efficient transfer method following the synthesis to locate the sample onto diverse substrates is a prerequisite. We thus transferred layer-controlled MoS2 onto PET films using our custom-made roll-to-roll transfer machine. Based on these results, it is envisaged that the cost-effective methodology will trigger actual industrial applications, as well as novel research related to 2D semiconductor-based multifaceted applications.

Resume : The transport behavior of a 60 nm thick MoS2 film is studied in a dual-gated field effect transistor (FET). At 300 K, the dual sweeps of the top and bottom gate fields give rise to spatial division of the conduction channel. Two separate channels simultaneously exist near the top and bottom gate dielectrics, whose existence is supported by their different threshold voltages (VTH) and the field effect mobilities (FE). Higher field effect mobility is observed from the top than the bottom conduction channel, whereas a lower threshold voltage is observed in the bottom channel. The segregation of carrier transport between the top and bottom channels is attributed to electrostatic screening of the gate field and the interlayer resistance of MoS2. Transport behavior of a single channel was probed when the temperature was below than 100 K. It results from the increased high interlayer resistance at low temperature that closes the conduction channel in the vertical direction to the bottom gate. When 100 K < T < 300 K, both the top and bottom conduction paths show different temperature-dependence of FE; μ_FE~T^(-1.2) and μ_FE~T^(-0.5) for the top and bottom channels, respectively. However, when T < 100 K, the temperature dependence converges to μ_FE~T^(-1.8), similar to the behavior in bulk MoS2. In addition to the transport properties, the separate control over the conduction channel in thick MoS2 enable us to propose a new device structure that can be further developed to a vertical inverter inside a single MoS2 flake.

Resume : Over the past few decades, semiconducting chalcogenides compounds (A2B3 with A = Sb, Bi, As and B = S, Se, Te) have been receiving much attention because of their wide range of applications in various field of science and technology. One of the most promising areas is their use in thermoelectric refrigeration.Various researches can be found on metal chalcogenides TE materials (Bi2Te3, PbTe, AgPbmSbTem+2, In4Se3, Cu2Se, Cu1.97S etc.). These materials become important in last few decades due to their enhanced ZT values. However aforementioned materials have the disadvantages that they contain high toxicity, high cost elements. Therefore incentive exists for researcher to develop alternative material. Sulphide based metal chalcogenides (Bi2S3, Cu2-xS, CdS, TiS2, Ag2S etc. ) as TE material finds high interest due to their low cost, low toxicity, more abundance and optimizable TE property. Various strategies such as doping have been used for improving its TE performance. Here we report the synthesis and thermoelectric properties of SPSed Bi2S3 and enhanced its performance by using x-mole% of CaCl2 as dopant. Powder in stoichiometric compositions were mixed and synthesised by melt and grow process inside a quartz evacuated tube. The as synthesised ingot were grounded and sintered by SPS. XRD of all samples shows single phase formation. All the compositions show a negative Seebeck coefficient suggesting n-type behaviour. The increasing dopant concentration leads to the improvement in its electrical property and after an optimized value it decreases. As a result a higher power factor ~500 μW/m-K2 for CaCl2 as dopant. ZT values greater than 1 was achieved in these halide doped chalcogenides.

Resume : During the past years, the development of industrialization and urbanization all around the world is causing an exponential increment of the presence of air pollutants such as NO2, SO2, O3, CO, etc. According to the Health Effects Institute (HEI), more than 95% of the world's population is breathing air that contains unhealthy levels of pollution, while 60% of the world lives in areas that do not even meet the most basic air quality standards. Therefore, to contribute to the control of air pollution, the development of devices and materials capable of detecting those polluting agents is vital. In this work, the effect of pore size on the adsorption and the electronic properties of hydrogenated porous silicon (pSi) was studied by means of Density Functional Theory. The nanopores are modeled by removing columns of atoms along the [001] direction of an otherwise perfect bulk Si crystal, according to the supercell scheme. Three different pore sizes were obtained: 38%, 28% and 20% of porosity. All surfaces were passivated with hydrogen atoms. The interaction of CO and NO on the nanostructure’s surface is analyzed through their adsorption energies; also, the electronic band structures and densities of states were obtained. The calculations indicate that the band gaps of the pSi-molecule systems depend on the pore size and the adsorbed species. This may open the possibility to electrically detect the bonding of the molecule on a surface dangling bond. The bond lengths are similar between all passivated nanopores for a given molecule. On the other hand, the adsorption energy changes according to the pore size and the toxic agent, being stronger for NO adsorbed on pSi (bonding by N). This study may contribute to the fundamental understanding of molecular adsorption on nanostructures that, in turn, could lead to the development of sensing devices.