Integration of advanced materials on silicon: from classical to quantum applications

Resume : High-electron mobility III-V semiconductors, ranging from InP, GaAs and the InGaAs system, have been widely studied as replacements for the n-type channel material in CMOS technology, where they may offer increased drive currents at reduced drive bias. While III-Vs are also widely used in standard HEMT technology for high-speed and mm-wave applications, as well as in photonics applications, integration on Si substrates remains challenging. The opportunities from such integration schemes are several, e.g. utilization of existing infrastructure and methods established by Si technology, reduction of costs and enabling of new functionalities. In particular, monolithically integrated III-V RF-devices with Si CMOS, for instance performing digital signal processing, could improve upon the functionality currently supplied by Si RF-CMOS technology. Several challenges must be met to successfully integrate III-V devices on Si, e.g. the transfer of a complex heterostructure onto a Si substrate without significant loss of carrier mobility, as well as the utilization of a Si CMOS-compatible process flow. In this work, we demonstrate an integrated III-V-on-CMOS technology platform, including a wide range of devices. In particular, we show high-performance logic FETs, high-frequency MOSHEMTs with record performance, as well as optical modulators, all integrated on Si substrates, including demonstrations of 3D sequential integration on Si CMOS.

Resume : Merging unique performance of compound semiconductor (CS) III-V materials in optoelectronics, high frequency and power devices with mature Si manufacturing is a holy grail of modern semiconductor technology. The difference between lattice constants, processing, and chemistry are just a few major challenges to be resolved. With practically non-existing methods for studying nanoscale physical properties of these buried structures, we developed a new concept for fast and efficient 3D nanoscale resolution quantitative mapping of physical properties of CS materials and devices. We combine novel nano-sectioning using variable energy Ar ion beam targeted at the edge of the sample to create a perfectly flat oblique near-atomic flat section through all layers of interest, and the material sensitive scanning probe microscopy (SPM), to reveal 3D morphology, composition, strain and crystalline quality via local physical properties – mechanical and piezoelectric moduli, nanoscale heat conductance, workfunction and electrical conductivity. We can observe the propagation of antiphase domains (APD) from the GaAs-Si interface through the 3D structure, reporting for the first time APD effect on electronic properties of multiple quantum wells that are electrically short the structure evident on charge distribution nanomaps. In GaN nanowires, we directly observe NW/Si substrate interface, and unexpectedly find the in-NWs domains of the opposite polarity via piezoelectric moduli maps. The novel paradigm will make a disruptive change on how 3D structure and physical properties of CS and microelectronics materials and devices are currently studied.

Resume : Strain engineering is a widespread and effective method in microelectronic to tune semi-conductors properties. For example, applying elastic strain can increase charge carriers’ mobility in silicon based transistors [J. Li et al , 2003]. Our group has developed a new approach to prepare strainable Si thin-films, using transfer on a flexible polymer substrate. Typical Si film thickness range between 20 and 200 nm, over a 200 mm diameter [P. Montméat et al. 2016]. The flexible polymer substrate enables mechanical deformation of the silicon thin film. Moreover, at the nanometric scale, silicon can reach several percent of elastic strain [H. Zhang et al., 2016]. The work presented here describes how ultra-thin monocrystalline silicon films are transferred on different polymer substrates. We also performed tensile tests on resulting samples using uniaxial tensile stage and bulge test. Full strain tensor and crystal orientation were measured using X-rays Laue micro-diffraction at ESRF beamline BM32. In situ measurements over macroscopic areas showed that a high homogeneous strain (>1%) was achievable on a macroscopic area in a silicon on polymer film using external uniaxial or biaxial load. In addition, mechanical coupling between the flexible substrate and silicon film was studied. These promising results should allow us to reach even higher strain level in silicon or in other semi-conductor materials.

Resume : Hydrogenated amorphous silicon nitride films (a-SiNx:H) have been investigated as gas barrier films for a long time. In this paper, a-SiNx:H films grown by roll to roll PECVD with various process conditions at low temperature were investigated from the point of view of correlation between microstructure and gas barrier properties. The chemical compositions and bond densities of the films were confirmed using FTIR and other analytical techniques and were compared by WVTR. Under the optimum condition, the WVTR of a-SiN:H single-layer on PET which is coated with organic planarization layer was reached down to 0.003g/m2·day and showed excellent mechanical flexibility with the failure bending radius of below 2mm.

Resume : Optically pumped GeSn laser have been realized, thus alloying of group IV elements germanium (Ge) and tin (Sn) has a large potential to be a solution for Si-photonics, since a direct bandgap for Sn incorporations above ~9 at.% is obtained. The value of the bandgap can further be controlled by adding Si into the mix, which can be exploited for the formation of heterostructures for carrier confinement. However, a sufficiently large difference in energy ΔE between the indirect L-valley and the direct Г-valley is required to achieve room temperature lasing. Recently lasing was reported at 280K in GeSn alloys with Sn concentrations as high as 22,3%. Alternatively ΔE can be increased by adding tensile strain to the GeSn layers. Here we will discuss that an appropriate combination of Sn concentration and strain will be advantageous to tailor gain and temperature stability of the structures. A comprehensive characterization of multiple quantum well (MQW) structures, formed from active GeSn layers and SiGeSn claddings. Spectra of optically pumped µ-disc MQW laser taken at various optical pump power. The data reveal a lasing threshold at 20 K from light in/light out curves of 39 kW/cm2, evidencing the superiority of MQW structures over bulk layers. Moreover, GeSn layers with only 6% Sn have been transferred and encapsulated with SiNx layers to add up to 1.3% tensile strain to the GeSn layers. Microdisc lasers fabricated using this technology exhibit thresholds of 0.8 kW/cm2 for pulsed pumping and around 1 kW/cm2 for CW pumping, which is dramatic reduction compared to previously reported GeSn bulk laser. The maximal lasing temperature is around 60K. The potential of combining tensile strain and GeSn laser structures harbouring 8-12% Sn will be discussed.

Resume : The deposition of a few monolayers of tin (Sn) on germanium (Ge) presents intriguing pathways towards both the formation of Ge/GeSn/Ge multi-quantum-wells [1] as well as stanene, a Sn-based two-dimensional topological insulator [2]. However, detailed studies of the adsorption and nucleation properties of Sn on Ge surfaces remain limited. Here, we provide an atomic-scale description of the formation of sub- to closed monolayers of Sn on both Ge(100) and Ge(111) surfaces using scanning tunneling microscopy. For both surface orientations we confirm that room temperature deposition results in the partial incorporation of Sn atoms into top surface layer. Based on density functional theory simulations of the local density of states, contrasted with scanning tunneling microscopy and spectroscopy, we provide insights into the contribution of ejected Ge atoms on the chemical composition of the surface features observed. Finally, to achieve truly atomically abrupt Ge/Sn interfaces we aim to suppress immediate Sn incorporation upon adsorption by varying the Sn deposition rate and substrate temperature. Overall our results add to a deeper understanding of the first stages of Sn/Ge growth, from which optimized growth processes may be derived. References: [1] F. Oliveira et al., Appl. Phys. Lett. 107, 1 (2015). [2] Y. Fang et al., Scientific Reports 5, 14196 (2015).

Resume : While the Ge-Sn material system is a promising candidate for Si-CMOS compatible electronic and photonic devices [1], very few studies have been devoted to the fundamental understanding of the Sn/Ge heterointerface properties. To investigate the initial formation of the interface and the electronic structure, we have grown Sn for different monolayer (ML) coverages on Ge(001) under UHV conditions. The surface electronic structure has been investigated by angle-resolved photoelectron spectroscopy, supplemented by other characterization methods. We find that the initial formation of the Sn wetting layer is dominated by ad-dimers of Sn and that the Sn introduces at sub-ML coverage an upward band bending. Moreover, the metallic nature of the Ge(001) surface vanishes upon Sn deposition and then returns at ~4 MLs of Sn. This is accompanied by the appearance of a Sn-related feature at 1.1 eV below the Fermi level, whose origin is under scrutiny. Interestingly, we observed that Sn-Ge intermixing occurs even at room temperature and will discuss the influence of the Sn on the effective masses of the light- and heavy-hole bands. Overall our study helps to better understand the Sn/Ge(001) interface and should motivate similar investigations directed to (Si)GeSn. References: [1] S. Wirths et al., “Si-Ge-Sn Alloys: From Growth to Applications”, Prog. in Crys. Grow. and Char. of Mat., vol. 62, pp. 1-39, March 2016

Resume : GeSn is a promising material for economically viable IR electro-optical devices, thanks to the possibility of monolithic integration on Si substrates. The substitutional incorporation of a few atomic percent of Sn allows to shift the direct bandgap of pure Ge past 1550 nm. Issues associated to the fabrication of GeSn thin films are the low solubility of Sn in Ge (< 1%at) at room temperature, and the large lattice mismatch (> 4.2%) of GeSn on Si. In this work, we present the growth of epitaxial GeSn thin films for IR photodetectors. Films are deposited on Si, Ge and graphene substrates through the use of magnetron co-sputtering. Different alloy compositions up to 10%at Sn are obtained by fixing the Ge target power and varying independently the Sn target power. We will show the potential of the sputtering technique to obtain high-quality crystalline GeSn below 300˚C, with thicknesses up to 500 nm. Characterizations include Raman spectroscopy, X-Ray diffraction, RBS, SEM and TEM imaging. Absorption coefficients and photoconductivity of the films with different Sn content will be presented as well as some proof-of-concept photodetectors.

Resume : Group IV elements of silicon and germanium are basic materials for photo detection. Further extension of detection range to the mid-infrared region can be performed by few schemes. Among them, the all group IV alloy of germanium-tin (GeSn) based material has shown promising characteristics for near infrared. Therefore we focused our study on optoelectronic properties of thick Ge0.96Sn0.04 layers on silicon modified by powerful pulsed laser radiation for enhancement of solubility of Sn atoms. The main material parameters relevant for photo-detectors are carrier lifetime, diffusion coefficient and diffusion length. We employed contactless optical techniques as differential transmittivity, differential reflectivity, and light induced transient grating for their nondestructive determination in GeSn layer which was converted to graded-bandgap structure by Nd:YAG laser irradiation due to thermogradient effect. The TEM/EDS cross-section analysis, X-ray photoelectron spectroscopy, Raman and UV reflection spectra confirmed the increase of Sn atomic content at the surface by order of magnitude. The determined slow free carrier lifetimes by differential transmittivity were in 20-30 ns range and weakly dependent on excitation, whereas differential reflectivity provided faster decays due to surface recombination. Increase of differential reflectivity signal in strongly irradiated sample verified reduction of carrier mass in the direct GeSn bandgap by 3 times with respect to indirect one before irradiation. Latter bandgap conversion occurs approximately at 50 nm depth. Surface irradiation by 1064 nm laser for Sn redistribution by thermogradient effect did not induce appreciable changes of recombination parameters. The work was supported as part of the Program on Mutual Funds for Scientific Cooperation of Lithuania and Latvia with Taiwan project: GeSn-based photo sensor - from basic research to applications.

Resume : 2D materials have been the focus of intense research in the last decade due to their unique physical and chemical properties. This presentation will highlight our recent progress on the synthesis of two-dimensional transition metal dichalcogenides (2DTMDs) for nanoelectronics applications using atomic layer deposition (ALD). ALD is a chemical process that is based on self-limiting surface reactions and results in ultrathin films, with sub-nm control over the thickness and wafer-scale uniformity at low temperatures. ALD-grown 2DTMD films typically exhibit a high density of out-of-plane 3D structures in addition to the desired 2D horizontal layers. The presence of such 3D structures can hinder charge transport, which hampers device applications. In this work, we first investigated the growth mechanism of the 3D structures by extensive high resolution transmission electron microscopy analysis. We found that the fins typically originate at the grain boundaries in the 2D layers and that the grain orientation of adjacent 2D crystals play an important role in 3D structure formation. Furthermore, we found that the density of 3D structures can be suppressed by introducing a novel three step (ABC) ALD process, which involves the addition of an extra Ar and/or H2 plasma step (step C) to the conventional AB-type ALD process. This reduces the 3D structure density and consequently reduces the resistivity of the TMD film by an order of magnitude. Our work showcases the versatility of plasma-enhanced ALD for the controlled synthesis of transition metal dichalcogenide nanolayers, which can enable applications in nanoelectronics

Resume : The graphene/silicon (Gr/Si) junction has been the subject of intense research activity for both the easy fabrication and the variety of physical phenomena involved. It offers the opportunity to investigate new fundamental physics at the interface between a 2D semimetal and a 3D semiconductor, and holds promises for a new generation of graphene-based devices such as rectifiers, photodetectors, solar cells, and chemical-biological sensors. A Gr/Si junction with defect-free interface exhibits rectifying current-voltage characteristics, owing to the formation of a Schottky barrier as in traditional metal-semiconductor (M/S) Schottky diodes [1]. The vanishing density of states at the graphene Dirac point enables Fermi level tuning and hence Schottky barrier height modulation by a single anode-cathode bias. When the Gr/Si junction is used as a photodetector, graphene acts as the transparent pick-up electrode as well as the active material for light absorption and electron-hole generation and separation. Although most of the incident light is converted into photo-charge inside Si, the absorbance in graphene enables detection of photons with Si sub-bandgap energy through internal photoemission over the Schottky barrier [2]. Photo-charges injected over the Schottky barrier, under high reverse bias, can be accelerated by the electric field in the depletion region of the diode and cause avalanche multiplication by scattering with the Si lattice, thus enabling internal gain. The Gr/Si junction forms the ultimate ultra-shallow junction, which is an ideal device to detect light absorbed very close to the Si surface, such as near- and mid-ultraviolet. In this talk, I start with some key features the graphene/semiconductor heterojunction, then I present the electrical characterization and the photo-response of two types of graphene/Si devices, on flat [3,4] and nanotip-patterned [5] Si-substrate, respectively. Although due to different mechanisms, for both devices, I demonstrate a photo-responsivity exceeding is competitive with present solid-state devices. I will show that the high responsivity can be attributed to charges photogenerated in the surrounding region of the flat junction [5] or to the internal gain by impact ionization caused by the enhanced field near the nanotips [4]. [1] A. Di Bartolomeo, Graphene Schottky diodes: An experimental review of the rectifying graphene/semiconductor heterojunction, Physics Reports 606 (2016) 1-58 [2] A. Di Bartolomeo et al., Graphene-Silicon Schottky Diodes for Photodetection, IEEE Transactions on Nanotechnology 17 (2018) 8408514, 1133-1137 [3] A. Di Bartolomeo et al., Hybrid graphene/silicon Schottky photodiode with intrinsic gating effect, 2D Materials 4 (2017) 025075 [4] G. Luongo et al. Electronic properties of graphene/p-silicon Schottky junction, Journal of Physics D: Applied Physics 51 (2018) 255305 [4] A. Di Bartolomeo et al., Tunable Schottky barrier and high responsivity in graphene/Si-nanotip optoelectronic device, 2D Materials 4 (2017) 015024 [5] G. Luongo et al., I-V and C-V Characterization of a High-Responsivity Graphene/Silicon Photodiode with Embedded MOS Capacitor, Nanomaterials 7 (2017) 158

Resume : Transition metal dichalcogenides (TMDCs), especially MoS2, have been considered as highly scalable electronic materials to extend Moore’s law. Nevertheless, low mobility and high contact resistance still impose serious difficulties on TMDC electronics. In this research, we propose a novel WS2/MoS2 Van der Waals heterostructure field-effect transistor (FET), as next-generation device architecture. Compared to single MoS2 FET, this heterostructure can benefit from not only higher mobility (from 43.3 to 62.4 cm2V-1s-1) but also lower Schottky barrier height (from 120 to 52 meV). Such significant enhancement is mainly due to charge transfer effect across the heterostructure which is confirmed by both photoluminescence and electrical measurements. Moreover, a double heterostructure WS2/MoS2/WS2 was also investigated. The combination of two heterostructures with Van der Waals self-encapsulation can further boost the mobility up to 102.5 cm2V-1s-1 at room temperature and 204.3 cm2V-1s-1 at 30 K. This concept of heterostructure FET can also open a wide application in other 2D material electronics.

Resume : The search for 2D high-k dielectric nanosheets materials have been actively researched due to a versatile properties such as high dielectric permittivity, solution processibility, and great thermal stability. In addition, the development of flexible and transparent electronics required the advanced dielectric materials. 2D Dion-Jacobson phase nanosheets have been shown high-k dielectric permittivity properties, which are undisturbed for the thickness, even for thickness down to 20 nm. Moreover, these nanosheets are transparent and don’t require to do a post annealing process, so 2D nanosheets can be deposited on flexible substrate. Here, we firstly demonstrate the effect of A-site modified Dion-Jacobson phases layered perovskites Sr2Nb3O10 nanosheets to enhance their dielectric properties and realize flexible dielectric thin films on polymer substrate in MIM structure. Oxide/metal/oxide multilayer electrodes are deposited as top and bottom electrodes, and the nanosheets thin films are grown by Langmuir-Blodgett method in room temperature. This new and simply fabricated high-k dielectric thin film can be a new tool to develop next-generation flexible electronics.

Resume : The development of new synthesis techniques of various nanomaterials has spurred a huge interest from the scientific and engineering communities to understand the outstanding physical properties and their integration in various devices ranging from large area photovoltaic to nanoelectronics and nanosensors. Among these nanomaterials, silicon nanowires (SiNWs), offering an important surface to volumes ratios, have been extensively used in chemical or biological sensors. In this work we have successfully prepared vertically aligned and well controlled SiNWs using a metal assisted chemical etching (MACE) process. The evolution of the morphology and microstructure of the SiNWs have been investigated using scanning electron microscopy and atomic force microscopy. By varying the etching time, we were able to tune the SiNWs length from 5 to 12 µm. The large specific surface area of the SiNWs makes them a good candidate for surface-enhanced Raman spectroscopy (SERS) sensors. Hence, we covered the SiNWs surface by silver nanoparticles (Ag-NPs) to activate the SERS effect. The SERS of rhodamine 6G (R6G) has been investigated using Raman spectroscopy. AgNPs/SiNWs matrix shows significant higher Raman signal sensitivity than a planar framework of Ag nanoparticles adsorbed two dimensionally a flat silicon surface. A SERS detection limit of 10-8 M rhodamine in aqueous solution has been obtained. The observed SERS enhancement is believed to result from additional light harvesting enabled by the SiNWs morphology and by the ability of the Ag-NPs to absorb visible irradiation caused by various localized surface-plasmon-resonances, which in turn depend on the size and interdistance of the Ag-NPs.

Resume : The surface properties of vapor–liquid–solid grown Silicon Nanowire (Si NW), has been recently a concern. One reason is due to the ability of the top-atoms to control highly the electronic properties of the Si NWs. Results from electronic characterization such Kelvin Probe Force Microscopy and X-ray Photoelectron Spectroscopies, show un-expected shift in the Si2p3/2 binding energy which represents the surface Fermi Level (SFL) at the Si NW. The SFL moves towards the midgap after exposing the hydrogen terminated Si NW to oxide conditions. Two main types of oxides have been found, sub-oxide (Si 1, Si 2, Si 3) and full oxide (Si 4), interestingly, the sub oxide found to produce trap states that lead to hysteresis effect in the I-V curve, while reaching full oxide state we found that the surface states decrease dramatically, and significant change is observed. In addition, transition from n to p conductivity and SFL shift is observed in case of annealing while no change is observed in room temperature oxidation. This mainly occurring due to breaking the water process production in time of oxidation, where the annealing is breaking the equilibrium and lead toward one direction reaction. By consuming electrons, hole accumulation layer at the surface lead toward n to p transition of the FET device-based Si NWs and SFL shift toward midgap due change in carrier concentration. Quantitative correlation between surface properties and nanomaterial functionality is done which can advance the development of hybrid Si NW-based device technologies.

Resume : In this work one-dimensional silicon nanowires (SiNWs) with well controlled size and length have been synthesized via a silver-assisted chemical etching method. A very fine and homogeneous dispersion of silver nanoparticles (3–5 nm) inside SiNWs films was carried out by dip coating process. An analysis of the electrical properties evolution of a series of SiNWs thin films doped with small amounts of Ag under pure air and air with 300 ppm CO is presented. Ag doping improves the sensitivity and selectivity for CO detection. The SiNWs/Ag NPs matrix shows significantly higher electrical sensitivity than a pure SiNWs framework. The microstructural and morphology of the silicon nanowires has been examined by X-ray diffraction and scanning electron microscopy. By Varying the etching time, we were able to tune the SiNWs length from 5 to 12 µm. We find that tan optimal 5 min etching time leads to the highest CO sensitivity. A very low detection limit of 10 ppm been obtained. The observed electrical sensitivity enhancement is believed to result from the electrons exchange between Ag and SiNWs surface.

Resume : Plasmonics is one of the best-suited approaches for photonics applications in the mid-infrared. Based on the concept of surface plasmon polaritons, electromagnetic waves strongly coupled to the collective oscillation of free carriers, plasmonics offers the possibility to enhance the light-matter interaction. Plasmonics is mainly based on gold but it was recently demonstrated that alternative materials, such as heavily-doped semiconductors (HDSC), can be favourably used in the mid-infrared spectral range, and be compatible with Si technology. In this work, we will present how HDSC can be used as sensor in the infrared range notably with surface enhanced spectroscopy obtained on periodic arrays of nano-antennas developed on an InAsSb/GaSb platform. These nano-antennas of Si-doped InAsSb alloy are able to sustain localised surface plasmon resonances (LSPR) used in sensing experiments exploiting the strong electric field enhancement appearing at the HDSC surface. Adjusting the carrier concentration in the HDSC by the doping level allows to control the value of the plasma frequency which is linked to the LSPR frequency. The smaller the plasma frequency, the smaller the LSPR frequency. The nano-antennas have been fabricated by optical lithography and wet etching. As expected, when changing the size and the shape of the nano-antennas it is possible to cover a large spectral range and to be sensitive to the polarization of the incident light. Additionally, monitoring the carrier concentration of the InAsSb, make possible to lead up the maximum field enhancement in the targeted spectral range of the biomolecular fingerprints.

Resume : Plasmonic nanoantenna provide a technique to resonantly couple light to atoms or molecules at sub-optical wavelength scales to enhance the non-linear or quantum properties. At the visible and near infrared, metals such as Au and Ag provide high performance including 2nd and 3rd harmonic generation but can be too metallic for many applications at mid-infrared wavelengths. Doped semiconductors such as InP, InAs, InAsSb and Ge have been introduced providing tunable mid-infrared plasmonic platforms in the important molecular fingerprint region (6.7 to 20 µm) where molecular absorption spectroscopy has applications for security, point-of-care healthcare and environmental monitoring applications. Here we present doped Ge on Si plasmonic nanoantennas with 3rd order non-linear coefficients at mid-infrared wavelengths comparable to those of Au at visible and near infrared. The Ge was epitaxially grown on Si substrates using low energy plasma enhanced chemical vapour deposition. Antennas were fabricated using electron beam lithography and fluorine reactive ion etching with processes available in many silicon foundries. Third harmonic generation of Ge gap nanoantennas with lengths from 1 to 6 µm are presented for a constant 300 nm gap spacing. For samples with a plasmon wavelength of 9.7 µm pumped at 12 µm wavelength, clear 3rd harmonic generation is demonstrated at 4 µm with a cubic dependence on the pump power and a maximum conversion efficiency of 10^-5 for 3 µm long antenna arms.

Resume : A wide range of studies have been conducted on operational stability under various stress conduction, over the past decade since the transparent oxide semiconductor device study began.1 Recent, the oxide semiconductors such as InGaZnOx based TFTs have been successfully employed in pixel driver circuitry for commercial display applications.2 However, a variety of defects are occurring due to long-term stability of oxide semiconductors. Typical of these are the threshold voltage shift by the constant gate bias and current ability drop by high voltage pulsed type signal at the drain.3 This degradation is due to the ionic bond that oxide semiconductors naturally have and various ways of improving their characteristics are currently under study. In this study, we have investigated the defect generation caused by the electrical signals applied to oxide semiconductors and the influence of an impact ionization in the active layer. Amorphous oxide semiconductor is selected as the channel material for the n-type oxide transistors which is realized on top of insulating silicon oxide/silicon substrate. A 150-nm-thick Mo gate electrode and a 200-nm-thick silicon dioxide gate dielectric were successively deposited by sputtering method and chemical vapor deposition, respectively. The Mo source and drain electrode was utilized and patterned by conventional lithography process. The variation of the static and transient currents in TFTs after high-voltage drain pulse signal was investigated by measuring the transfer curves experimentally and simulated using the technology computer aided design (TCAD) 2D simulator (ATLAS, Silvaco Inc.). Here we reports that the reduction of current ability due to "impact ionization" and its effect on various structures. The contribution of the impact ionization in oxide semiconductors is verified through the TCAD simulation, and it was confirmed experimentally the effect of the impact ionization according to the device stacking structures. In addition, we reports on the effects of drain-induced source barrier lowering4 phenomena in InGaZnOx TFTs with asymmetrical local defect states. This effect has generally been observed in TFT structures with short channels, whereas the present study discovered it in a long-channel device with asymmetrical local defects. This work was supported in part by the DGIST R&D Program of the Ministry of Science, ICT, and Future planning (19-NT-01) and in part by the Basic Science Research Program through the National Research Foundation of Korea (NRF) under Grant NRF-2018R1D1A1B07041075. References 1 Nomura, K. et al., Thin-film transistor fabricated in single-crystalline transparent oxide semiconductor. Science 300, 1269-1272 (2003). 2 Fortunato, E. et al., Oxide semiconductor thin-film transistors: a review of recent advances. Advanced Materials 24, 2945-2986 (2012). 3 Lee, H.-J. et al., Impact of transient currents caused by alternating drain stress in oxide semiconductors. Scientific Reports 7, 9782-9790 (2017). 4 Lee, H.-J. et al., Drain-Induced Barrier Lowering in Oxide Semiconductor Thin-Film Transistors with Asymmetrical Local Density of States, IEEE J. Elec. Dev. Soc. 6, 830-834 (2018).

Resume : Silicon is the most widely used and better known functional material. Nano- and hetero-structures have been used to improve the performance of Si-based devices. The specifications of future-generation devices require to use materials and structures with even higher efficiency and also IC compatible. Here, we discuss how nanoscale non-uniformity can provide improvement of multiple transport properties of semiconductor nanostructures and lead to efficient heat management and thermoelectric energy conversion at the nanoscale. We show that synergy of several effects can give simultaneous decrease of the thermal conductivity and enhancement of the electrical properties in nanostructures with geometrical and compositional non-uniformity [1,2,3]. It is shown that quantum effects and the presence of quasi-localized states can further enhance the thermoelectric efficiency and control heat conduction [4,5]. [1] ‘Synergy between defects, charge neutrality and energy filtering in hyper-doped nanocrystalline materials for high thermoelectric efficiency’, X.Zianni and D. Narducci, Nanoscale (2019) [2] ‘Scaling behavior of the thermal conductivity of width-modulated nanowires and nanofilms for heat transfer control at the nanoscale’, X. Zianni, V. Jean, K. Termentzidis and D. Lacroix, Nanotechnology 25, 465402 (2014) [3] ‘Diameter-modulated nanowires as candidates for high thermoelectric energy conversion efficiency’, X.Zianni, Applied Physics Letters 97, 233106 (2010) [4] ‘Coulomb oscillations in the electron thermal conductance of a dot in the linear regime’, X. Zianni, Physical Review B 75, 045344 (2007) [5] ‘Large thermoelectric power factor enhancement realized in InAs nanowires’, P.M. Wu, J. Gooth, X.Zianni, S. Fahlvik Svensson, K.D. Thelander, C. Thelander, K.Nielsch, H. Linke NanoLetters 13, 4080 (2013)

Resume : Elastic strain is routinely used to improve transport and optical performances of SiGe based devices because of the influence of lattice deformation on the electronic band-structure. Nevertheless, the mismatch between the Si and Ge lattice expansion coefficients originates a temperature- dependent contribution to the strain field with a relevant impact on the electronic spectrum. In this talk, we report a comprehensive analysis of thermo-mechanical properties of strained Ge microstructures with different geometries and different strain configurations. We discuss their impact on the photoemission properties, disentangling the contributions of mechanical deformations induced by stressor layers from the effects of the thermal components of the strain field. We first compare strain maps obtained with µ-Raman experiments at different temperatures with theoretical predictions based on FEM mechanical simulations combined with a perturbative approach, assessing the influence of strain and local heating on the Raman shift. Subsequently, we probe the effect of the strain field on the valence and conduction band edges by means of spatially resolved µ-PL experiments, interpreted in the framework of a theoretical model based on the deformation potential approach. With this comprehensive approach we show the potential benefits of strained structures as building blocks of opto-electronic applications offering guidelines for their design, optimization and integration in Si platforms.

Resume : Increasing the carrier concentration in epitaxial Ge and GeSn above 1e19/cm^3 poses a challenge from a defect point of view, as compensating defects are abundantly created in the growth of the layer. As the intent is to further increase the carrier concentration above 1e20/cm^3 and semiconductor doping starts to resemble more alloying than traditional doping, we are entering unfamiliar territory when it comes to defect dynamics. We have used positron annihilation spectroscopy (PAS) in combination with density functional theory (DFT) calculations to study compensating vacancy-donor complexes in epitaxial layers of Ge and GeSn doped with P and As. As expected the dopants form complexes with the native vacancy defects. In previous studies both mono- and divacancy complexes have been observed in highly doped Ge. Whereas monovacancy complexes dominated in diffusion doped bulk Ge, divacancy complexes were observed in implanted and laser annealed Ge. From the experimental results it is clear that monovacancies dominate the positron annihilation in all studied epitaxial layers. DFT calculations indicate that Sn does not have the desired effect of trapping vacancies, as the binding energies for V-Sn pairs is clearly lower than for complexes involving dopants. However, both experimental and computational PAS results indicate that Sn is having an impact on the annihilation state of the positrons.

Resume : The n-type doping of Ge and Ge-based alloys is a self-limiting process due to the formation of vacancy-donor complexes (DnV with n ≤ 4) that deactivate the donors. This work clearly demonstrates that the dissolution of the DnV clusters in a heavily n-doped Ge, GeSn and SiGeSn layers can be achieved by millisecond-flash lamp annealing. This DnV cluster dissolution results in a considerable increase of the electrical activation together with a suppression of donor diffusion. Using electrical measurements and positron annihilation lifetime spectroscopy, combined with theoretical calculations, it is possible to address, understand and solve the fundamental problem of achieving ultra-high doping level in Ge, that has hindered so far the full integration of Ge and Ge-based alloys with complementary-metal-oxide-semiconductor technology. This work is partially supported by the National Science Centre, Poland, under Grant No. 2016/23/B/ST7/03451.

Resume : A highly-doped epitaxially-grown source/drain is a key element for the development of the next-generation of transistors such as FinFET and GAA, where a high active dopant concentration is required for the device optimization. This in turn requires a deep understanding of the defect formation mechanisms related to the dopant deactivation. This paper presents a density functional theory study of the dopant-defect complex formation in P and As co-doped Si layer (Si:P+As). Emphasis is placed on the impact of As co-doping on the defect formation in Si:P. Numerical results indicate that for both P and As, a stable deactivation vacancy (V) complex in Si is DxV (D = P or As, x = 1–4), where the V is surrounded by dopants. The formation enthalpy of AsxV is lower than that of PxV, implying that As traps V more efficiently than P. In turn, As co-doping is expected to help increasing the active P concentration by releasing them from the complex. In addition, our simulation results indicate that a stable interstitial dopant-based complex in Si is a split interstitial (S), where two deactivated dopants occupy one Si site. As is found to form more likely S in Si than P at high dopant concentration, implying that solubility of As in Si is lower than that of P. Our simulations suggest that at low concentration, As co-doping with Si:P enhances the P activation. This is in good agreement with our experimental observations, where a 1.2 % As+P concentration grown at 450°C leads to a higher active dopant concentration than for Si:P alone.

Resume : Materials consisting of silicon nanocrystals (Si-ncs) embedded in SiO2 are the subject of an intense research activity due to their potential applications in optoelectronic. Providing charged carriers by introducing n- or p-type impurities in the core of Si-ncs can drastically modify their properties. A perfect control of the doping level should allow to tune the material properties for specific applications. In fact, it has been shown that highly P or B doped Si-ncs should exhibit strong plasmonics properties. However, due to the low solubility of impurities in silicon and side effects like self purification (i.e. impurities are expelled toward Si-ncs), reaching high doping level could be difficult. To understand and to improve the quality of these systems, an accurate control of the dopant location is necessary. In this work, n- (P, As) and p-type (B) doping carried out by co-implantation with Si in SiO2 thin films annealed at 1000°C have been investigated using Atom Probe Tomography. By computing 3D mapping of chemical species, we studied the structure of these films at the atomic scale to investigate the location of dopants and the Si clustering characteristics along the implantation profile. We highlighted an influence of the dopant nature on the Si-ncs growth and showed that high level of n-type impurities can be introduced in the core of every Si-ncs. Behavior of p-type doping will be discussed and seems different, with only low level doping observed in some Si-ncs.

Resume : Many quantum optics, quantum communications and quantum information processing systems require single photon detectors. Superconducting devices have demonstrated the highest single photon detection performance but require cryogenic cooling. Below 1 µm wavelength, CMOS single photon avalanche detectors (SPADs) provide 300 K operation. For short wave infrared wavelengths as required for telecoms or superior imaging through atmospheric obscurants, InGaAs SPADs are commercially available and operate on Peltier coolers. Here we present Ge on Si SPADs operating with 38% single photon detection efficiency at 1310 nm and 125 K. Results will be presented from devices ranging from 100 µm diameter to 25 µm diameter with the smallest devices demonstrating jitter of 150 ps with dark count rates of 2830 Hz for 2.48% excess bias and NEP of 4 x 10^-17 W/√Hz at 125 K. The devices demonstrate Geiger mode operation up to 200 K and afterpulsing levels are at least five times lower than InGaAs devices under nominally identical conditions. The wavelength dependence will be presented with the direct band edge at 150 K being about 1500 nm above which the SPAD performance decreases significantly. Approaches to increase the performance to 1550 nm will be discussed. A review of single photon applications will be discussed. Initial lidar results will be presented demonstrating the ability to range over km distances and hundreds of metres through obscurants at eye safe powers at 1450 nm wavelength.

Resume : Silicon-germanium is a material of interest for silicon photonics research and industry related activities where high-performance modulator and detector devices working in the C band are required. For optimal operation of electro absorption modulators such as Franz- Keldysh effect a high-quality material coupled to a precise composition of the material is of outmost importance. We report for the first time a GeSi heterostructure EAM modulator demonstrating performance up to 56Gb/s and a Rapid Melt Growth (RMG) deposition method of SiGe forming crystalline structures embedded in an SOI platform. The RMG based SiGe composition is uniform over the length of the SiGe wires and demonstrate tunability of the composition of SiGe using a single deposition process. This method is suitable for waveguide integration on the SOI platform which is crucial for multi wavelength operation of Franz Keldysh type modulators.

Resume : The epitaxial growth of germanium on silicon is a basic requirement in many fields, such as electronics and photonics. However, the mismatch in lattice parameter and thermal expansion coefficients results in defective epitaxial layers and reduced device performance. A novel approach, named vertical heteroepitaxy (VHE), has been recently demonstrated to address these issues. VHE employs deep patterning of Si wafers to obtain the vertical growth of a self-assembled array of Ge micro-crystals by Low-Energy Plasma-Enhanced CVD (LEPECVD). Such crystals have been demonstrated to be fully relaxed and have a high crystalline quality, while featuring the complete expulsion of threading dislocations. We aim to exploit VHE to grow an array of microSPADs (i.e. single photon avalanche diodes) operating in the visible to NIR range by depositing Ge on top of Si micro-crystals, featuring a carefully designed doping profile required by SPAD operation. SPADs are very sensitive to material quality, requiring optimal deposition conditions. Here we show the morphological (e.g. crystal faceting) characterization of Si micro-crystals by means of SEM imaging and FIB/SEM tomography as a function of deposition parameters and substrate patterning, and the conditions we selected for device growth. We then briefly show the deposition process of doped Si micro-crystals and some preliminary characterization of the doping profile, in the form of I-V curves from single micro-crystals and SIMS measurements.

Resume : Defect-enhanced quantum dots are all-group-IV room-temperature light-sources consisting of epitaxial Ge/Si quantum dots (QDs) and extended point defects that are intentionally introduced upon low energy ion implantation. Both carrier types, electrons and holes, are confined within the QD region, i.e. holes experience quantum confinement due to the large band offsets between Si and Ge, while electrons are trapped by introduced defects of split-[110] self-interstitial structure. The most prominent features of DEQDs are clear signs for optically-pumped lasing, absence of thermal quenching of the photoluminescence emission up to room-temperature, and the demonstration of LEDs, grown directly on Si working efficiently up to 100°C. Here, we present in a combined experimental and theoretical approach that the ~3.5% biaxially compressively strained Ge on Si “hut-cluster” QDs used up to now seem to be all but ideal host matrices for the light-emitting defects in DEQDs. Theoretical calculations based on density functional theory suggest that reducing the amount of compressive strain in the QD leads to a strong enhancement of the oscillator strength of the radiative transitions in this interlaced defect-QD system. Experimental evidence for improved photoluminescence emission for less-strained DEQD-systems as well as means to arbitrarily strain the DEQDs using thin DEQD membranes on piezoelectric actuators will be presented. These findings can be the key to tap the full potential of DEQD light-sources for applications in the field of Si photonics and beyond.

Resume : Ge epitaxially grown on Si is an ideal material for an integrated photonics platform with low absorption between 1.8 µm and 14.5 µm wavelengths. Label free sensing is typically undertaken using Fourier Transform InfraRed (FTIR) spectrometers within the fingerprint region (6.7 to 20 µm) providing many absorption lines specific to individual molecules including explosives, bioweapons, bio-markers for point of care medical diagnosis and environmental pollutants. We present Ge on Si waveguides with waveguide losses measured between 7.5 to 11 µm wavelength and demonstrate losses as low as 1 dB/cm at 10 µm. Analysis will be presented which identifies the higher loss mechanisms at lower wavelengths and how these may be reduced to 1 dB/cm or less. The Ge waveguides are used to demonstrate evanescent molecular absorption spectroscopy between 7.5 to 11 µm wavelength and the results are compared to FTIR spectroscopy. Poly(methyl methacrylate) (PMMA) and acetone are measured with the Ge waveguides demonstrating significantly longer absorption lengths potentially allowing a significant increase in sensitivity despite low overlap of the optical mode with the analyte. A route to single chip spectroscopy systems using the Ge on Si mid-infrared photonics platform will be presented detailing the key source, sensor and detector criteria required for parts per million or better detection sensitivity suitable for a wide range of security, healthcare and environmental sensing applications.

Resume : III-V semiconductors present interesting properties and are already used in electronics, lightening and photonic devices. More particularly alloys containing Ga, In and Sb are increasingly used by the semiconductors industry for high frequency operation, WIFI technology, high power devices, lasers for communications, sensors… This sector accounts for about 90% of world consumption of gallium for example. With the huge increase of IoT devices there is a real challenge to be able to minimize the consumption of these elements or substitute them by more abundant ones to fulfill the same function. Among the envisaged solutions, replacing the III-V substrate by a silicon one and using selective hetero-epitaxy processes are very promising. In this contribution, we will review the different technologies compatible with large-scale integration to integrate III-V semiconductors to realize specific functions such as light emission and detection. An important aspect of the presentation will be devoted to MOCVD hetero-epitaxy of As and Sb based III-V compounds on large scale wafers. We will show that bulk material (InP, GaAs and GaSb substrates) could be substituted by thin layers elaborated on a standard Si(100) microelectronic substrates. Selective deposition will also be considered to put the materials only at the place where it is needed. The potentiality of these two approaches for photonic devices realization and more precisely lasers sources will be shown. As prospective solution, 2D materials monochalcogenides elaborated on large scale 300 mm Si substrates will be presented and their physical properties will be exposed. This work was supported by the French government managed by ANR , IRT Nanoelec ANR-10-IRT-05, ANR-15-IDEX-02 and LabEx Minos ANR-10-LABX-55-01

Resume : In recent years, germanium tin (GeSn) alloy has attracted growing attention for its potential integration into microelectronic and optoelectronic devices. Interestingly, GeSn belongs to group-IV semiconductor compounds, has a direct bandgap for Sn concentration greater than 8 at% with a low bandgap energy (< 0.66 eV at RT) and, moreover, has a very high hole mobility (> 1900 cm2/V.s). In this work, we report on the fabrication of GeSn nanowires (NWs) obtained by both « bottom-up » and « top-down » approaches. In the first approach, GeSn NWs were grown by chemical vapor deposition (CVD) using the vapor-liquid-solid mechanism with standard gaz precursors (GeH4, SnCl4). After optimizing growth conditions (temperature and SnCl4/GeH4 ratio) to get perfectly straight NWs, we mainly investigated the incorporation and spatial distribution of Sn in the NWs by Auger and EDX-STEM measurements. In the second approach, GeSn NWs were fabricated by dry etching of GeSn layers having different Sn concentration (from 6 to 15 at%) previously grown by CVD on virtual Ge buffer layers. Here, we pay attention to the surface roughness of vertical and horizontal NWs as a function of etching conditions. We will show that suspended horizontal NWs have been obtained paving the way towards the realization of GeSn Gate-All-Around NW MOSFETs.

Resume : THz quantum cascade lasers (QCLs) have been demonstrated in III-V materials, however being polar systems the QCL maximum operating temperature is limited by the electron-phonon interaction. From this prospective and for possible integration into CMOS processes, implementing the THz QCL architecture on non-polar SiGe system has a great technological relevance. Theoretical calculations showed that n-type Ge-rich heterostructures are the most promising. Here we study intersubband optical transitions and structural properties of n-type Ge/SiGe asymmetric coupled multi quantum wells grown by UHV chemical vapor deposition. Scanning transmission electron microscopy, atom probe tomography and X-ray diffraction measurements demonstrate the high material and interface quality and a very good composition and thicknesse¬¬s reproducibility. Fourier-transform infrared absorption spectroscopy measurements show intersubband (ISB) transitions among the confined states of the wells and indicate a high degree of control on inter-well coupling and electron tunneling [1]. These results combined with a modelling of the non-radiative lifetimes measured by pump-probe experiments allowed us to evaluate the system key parameters driving electron scattering. A theoretical description based on the non-equilibrium Green’s function formalism [2] was employed to assess the impact on gain of the interdiffusion length and interface roughness. Leveraging on the particularly low values of these parameters measured in our samples, the analisys suggests that laser operation can be achieved in optimized structures up to room temperature. 1. C. Ciano et al., Phys. Rev. Appl. 11, 014003 (2019) 2. T. Grange et al., Appl. Phys. Lett. 114, 111102 (2019)

Resume : Mid-infrared (MIR) photonics is receiving considerable attention due to the variety of envisaged applications in medical diagnostics, biochemistry studies, chemical analytics, and environmental monitoring for safety and security. Nowadays, commercially available MIR spectroscopic systems are based on bulky and expensive instruments and, as a consequence, there is an increasing demand for compact sensing solutions that can be used in remote areas. In this framework, group IV photonics is emerging as a promising option to realize portable MIR spectroscopic systems. The main rationales behind the use of group IV materials are the cost-effectiveness and the reliable manufacturing technology already developed for microelectronic industry and the wide transparency of Si and Ge in the MIR spectral range. Since broadband MIR light sources integrated on silicon are still not available, wavelength conversion through non-linear optical effects is strongly demanded. In this work we present the theoretical investigation and the experimental verification of second harmonic generation in hole-doped Ge/SiGe asymmetric quantum wells (QW). We have developed a model for the valence band structure of SiGe alloys to find the optimal QW design for second-harmonic generation. The designed heterostructure has been grown by low-energy plasma enhanced chemical vapor deposition and second-harmonic generation has been observed by both continuous wave pumping with a quantum cascade laser emitting at a wavelength of 10.4 microns, and pulsed pumping with an optical parametric amplificator tunable between 9 and 11 microns.

Resume : Germanium is the very attractive material for development of Si-compatible light source due to its compatibility with CMOS technology and small difference (136 meV) between the direct and indirect gaps, which can be reduced by application of tensile strain or n-doping. Combination of such two methods could provide mutual benefits and increase the direct-gap luminescence efficiency. In this work the influence of Sb doping on optical properties of n-Ge layers grown by MBE on Si(001) and Ge(001) substrates are discussed. The use of different substrates made it possible to reveal the impact of various defects on n-Ge layer luminescence. It was obtained that interplay between the positive impact of doping due to states filling in L valley and the negative one due to additional absorption losses and carrier lifetime shortening requires accurate selection of appropriate doping level. It was also shown that rapid thermal anneal could influence the Ge luminescence efficiency significantly and its impact depend on doping level [Semicond. Sci. Technol. 33, 124019 (2018)]. n-Ge/Si layers with optimal doping level were used for fabrication of locally tensile strained microstructures [Semiconductors 52, 1442 (2018)], including structures with improved heat sink. The latter circumstance made it possible to expand the range of used optical pumping power by more than order of magnitude. Usage of various microresonators compatible with locally strained Ge microstructures is discussed.

Resume : Abstract—Due to their high efficiency, III-V photovoltaic devices are very promising for terrestrial concentrator and space photovoltaics. Wide spread adoption of this technology would require significant improvement in efficiency and major cost reduction, in this talk I will review strategies and recent advances towards achieving these goals by using nanoporous semiconductors, nanocomposites and graphene based virtual substrates. Keywords— Virtual substrate, heteroepitaxy, mesoporous silicon, graphene, nanocomposites, photovoltaics Most optoelectronic devices such as lasers, photodetectors, and solar cells are made by the epitaxial growth of semiconductor heterostructures on monocrystalline wafers. Defect-free epilayers are a primary requirement to achieve a high-performance device. Today, the performance, the functionality, and the cost of those devices are restricted by the very few number of available monocrystalline wafers. In this talk, I will discuss different strategies to access cost-effective virtual substrates for germanium, III-V, IV-IV and III-N materials epitaxy. Among them, we have recently introduced a graphene-porous silicon nanocomposite compliant substrate. The idea behind this concept is to use a stretchable and flexible substrate such as porous silicon during the growth of lattice mismatch epilayers. Conceptually this allows the epilayer to elastically relax and transfer most of the strain to the flexible substrate. As a result, we would expect a reduction in misfit and threading dislocations formation during epitaxy. The process for making the substrate is very simple and scalable. To prove the concept, we have used a combination of Raman spectroscopy, X-ray diffraction reciprocal space mapping, scanning electron microscopy and transmission electron microscopy to study the strain and morphology evolution of the substrate after graphene deposition. We found that due to the unique flexibility of porous silicon the substrate allows to exceed critical thickness for plastic relaxation by 2 orders of magnitude. Additionally, thanks to the extreme temperature stability of the graphene coating, the substrate withstands temperatures up to 1050°C which makes it compatible with epitaxy of most technologically important semiconductor materials. Another new paradigm to reduce dislocation propagation by using nanoscale effects in plastically relaxed layers will be also reviewed, it is based on the use of nanovoids as dislocation barriers which block dislocations propagation. The interaction between dislocations and voids results in a significant reduction in TDD, making it a promising approach for the integration of optoelectronic devices on silicon. References: A. R. Boucherif, A. Boucherif, G. Kolhatkar, A. Ruediger, R. Arès, “Graphene–mesoporous Si Nanocomposite as a Compliant Substrate for Heteroepitaxy”, Small, 1603269 (2017). Y. A. Bioud, A Boucherif, M. Myronov, A. Soltani, G. Patriarche, N. Braidy, D. Drouin and R. Arès, “Highly scalable defect-free heteroepitaxy using nanovoids as dislocations barrier” Nature communications, (2019) revision

Resume : The epitaxy of Ge on Si is far from being lattice matched (4.2% difference between Si and Ge), making the growth of thick layers challenging. Several schemes have been explored in the literature to obtain Ge layers, such as a Low Temperature / High Temperature (LT / HT) approach followed by a cyclic anneal. Another interesting approach is to perform the heteroepitaxy of Ge in nanometer-size Si windows surrounded by SiO2. Some groups have succeeded in obtaining high quality Ge layers using nano-heteroepitaxy, but there was no analysis of defects generated with that approach. In this contribution, Ge epitaxy on nanometer-size Ge pillars was studied in a 300 mm industrial Reduced Pressure-Chemical Vapor Deposition tool. A patterning scheme based on diblock copolymer lithography was used to fabricate honeycombed nanometer-sized Si templates. The epitaxial growth of Ge nano-pillars at 600°C (with GeH4) was highly selective and uniform. Various thickness Ge layers grown with a LT/HT approach on Ge nano-pillars were characterized by Atomic Force Microscopy, X-Ray Diffraction and cross-sectional Transmission Electron Microscopy. The surface morphology of 2D Ge layers grown on Ge nano-pillars was degraded compared to that of layers grown on blanket, bulk Si. The other structural properties (the slight tensile strain, threading dislocations densities from XRD and so on) were quite similar, however. Stacking faults and twins otherwise appeared during the coalescence process.

Resume : In the quest for novel high performance devices, innovative architectures need to be developed by exploiting three dimensional heterostructures. This requires a fine control of the morphology and faceting of the crystal surface, particularly for self-assembled growth processes. Vertical structures can be obtained in out-of-equilibrium growth conditions, where the kinetics of adatom incorporation on the surface overrules the material redistribution driven by surface energy minimization. Here we present a comprehensive phase-field model [1] to predict the realistic growth pathway of semiconductor crystals in three dimensions. Simulation results focus first on the growth of Si and Ge microcrystals on Si pillars by reproducing the evolution of the faceted morphology, comparing different growth temperatures, deposition flux distributions and pattern orientations. Particular attention will be devoted to the faceting at the crystal top, composed mainly by {100}, {110} and {113}, which is more critical for optoelectronic performances. Then, GaAs nanomembranes obtained by selective area epitaxy [2] are investigated. The vertical growth is promoted by a large difference in the adatom incorporation time for {110} and {111}B surfaces, quantified by the model to be of one order of magnitude. Simulations capture also the more complex faceting found in experiments when rotating the pattern orientation. [1]Albani, Phys Status Solidi b, 1800518 (2019) [2]Albani, Phys Rev Materials 2, 093404 (2018)