Silicon compatible materials and integrated devices for photonics and optical sensing

Resume : Exploiting plasmonics for mid-IR sensing purposes has become an increasing area of research. The reason is that many molecules present molecular vibrational resonances, which provide spectral fingerprints in the near- and mid-IR region [1, 2]. Of particular interest is the gas detection, diagnostic and medical care. To this day, strong plasmon resonances in the visible and near-IR spectral range have been identified in nanostructured metals such as silver, aluminum and gold [3]. In principle, heavily doped semiconducting materials like Si or Ge could be an interesting alternative to replace metals due to their compatibility with CMOS technology. Indeed, the possibility to control the plasmon resonance frequency in semiconductors via the carrier density opens new route for near- and mid-IR detectors. In this work, we report on the strong mid-IR plasmon absorption from heavily P-doped Ge thin films obtained by non-equilibrium thermal processing. Ultra-doped Ge layers were fabricated by ion implantation of P ions followed by rear-side flash lamp annealing in the millisecond range. This approach, in contrast to conventional annealing procedures, leads to full recrystallization of Ge films and high P activation irrespective of pre-treatment. In this way, single crystalline Ge thin films free of defects with carrier concentration much above 1×1020 cm-3 and carrier mobility above 260 cm2/(V·s) were obtained. The mid-IR plasmon spectral response at room temperature from those samples was characterized by means of Fourier transform infrared spectroscopy. It is proven that the position of the signal from the plasmon resonance frequency can be tuned as a function of the P concentration. [1] A. G. Brolo, Nat. Photonics 6, 709 (2012). [2] N. Liu, M. Mesch, T. Weiss, M. Hentschel, and H. Giessen, Nano Lett. 10, 2342 (2010). [3] G. Konstantatos and E. H. Sargent, Nat. Nanotechnology 5, 391 (2010).

Resume : Despite continued research efforts, the photoluminescence (PL) quantum yield (QY) of Si nanocrystals (NCs) remains below approximately 30%, strongly inhibiting their application potential. In this work, colloidal dispersions of free-standing B/P co-doped Si NCs are developed in an attempt to engineer the most suitable Si NC ensemble for efficient down-conversion applications. An ideal ensemble has a high PL QY (at least 50%) and allows interactive electronic properties, such as exciton transfer and space-separated quantum cutting. Recently [1,2], the importance of NC size and dispersity was demonstrated in relation to PL QY, validating the necessity of being able to attain monodisperse ensembles of NCs at a desired size. Here we report on the results of our pursuit towards NC size selection using high-performance size exclusion chromatography (HPSEC) on free standing colloidal Si NCs. Subsequently, embedding of the colloidal NCs in a glass solid is explored to obtain solid structures with engineered inter-particle interactions. Our final goal is a stable solid state dispersion of Si NCs with high PL QY, and desired interactions. [1] Sugimoto, Hiroshi, et al. The Journal of Physical Chemistry C 117.22 (2013): 11850-11857. [2] Sun, Wei, et al. Advanced Materials 27.4 (2015): 746-749.

Resume : Heavily-doped semiconductor films are very promising for application in midinfrared plasmonic devices because the real part of their dielectric function is negative and broadly tunable in this wavelength range. In this work we investigate heavily n-type doped germanium epilayers grown on silicon by infrared spectroscopy, first principle calculations, pump-probe spectroscopy and DC transport measurements to determine the relation between the plasma edge and the carrier density and to quantify mid-infrared plasmon losses. We demonstrate that the screened plasma frequency can be tuned up to 1200 cm-1 and that the electron scattering rate is dominated by scattering with optical phonons and charged impurities. We also found weak dependence of losses and tunability on crystal defect density, temperature, inactivated dopant density and optical pump wavelength in the near infrared. Our results suggest that plasmon decay times in the picosecond range can be obtained in Ge. In order to assess the potentiality of our approach, we have processed nano-antennas out of the epitaxially grown n-type Ge films and demonstrated up to two orders of magnitude signal enhancement for the molecules located in the antenna hot spots. This result paves the way toward low-cost integration of plasmonic sensing platforms into the existing CMOS technologies. The research leading to these results has received funding from the European Union’s Seventh Framework Programme under grant agreement no. 613055.

Resume : Nanoscale heterogeneous catalysts are heavily involved in modern chemical production, as well as in pollution mitigation, and generally advantageous due to their high number of active sites per unit of material. Characterizing individual catalyst nanoparticles in operando is a dream of catalysis science because any detrimental ensemble averaging effects could be completely eliminated. For this reason, a number of approaches to study single nanoparticle catalysis are emerging (1). However, a method to directly correlate physical and chemical properties of single catalyst nanoparticles with their catalytic activity is still missing mostly because existing approaches monitor either only the catalyst or the reactants. In this work, we present our efforts towards correlating single particle plasmonic nanospectroscopy (2) and mass spectrometry to simultaneously monitor the catalyst state and activity/selectivity in operando at atmospheric pressure reaction conditions. We illustrate our concept on the example of hydrogen oxidation over Pt and a characterization of the kinetic phase transition (3) on nanoparticles of different size. References 1. Sambur JB & Chen P (2014) Annual Review of Physical Chemistry 65(1):395-422. 2. Syrenova S, et al. (2015) Nature Materials 14:1236-1244. 3. Larsson EM, Langhammer C, Zoric I, & Kasemo B (2009) Science 326(5956):1091-1094.

Resume : The increasing interest in on-chip biological and gas sensing requires the development of cheap and practical detectors operating in the Mid-Infrared (MIR) and, preferably, integrated on silicon. Due to their toxicity, high costs and non-integrability with Si, mercury-cadmium-telluride detectors, are not suitable for civilian applications. A possible approach is the exploitation of intersubband absorption based devices such as Quantum Wells Infrared photodetector (QWIPs). Here we present a p-type Ge/SiGe QWIP, in which the absorption take place in the valence band of the Ge QWs. The benefit in using p-type QWs lies in the possibility to operate at normal incidence thus not requiring complex architectures such as waveguides or gratings. Moreover, the use of p-Ge is favorable thanks to the larger absorption coefficient of Ge, compared to p-SixGe1-x, which has been used in the past due to the impossibility to grow high quality Ge rich material over Si. The easy tunability of the QWs thickness allows for the design of detectors working at a desired wavelength. We report here the absorption spectra, as measured by FTIR of a set of Ge/Si0.5Ge0.5 QWs strain symmetrized on a 1um thick Si0.2Ge0.8 relaxed buffer. The absorption peak shift for different QW thicknesses as measured by XRD and TEM is consistent with the QWIP design. The structural and optical properties observed, despite the thin relaxed buffer employed, are promising for the development of on-chip MIR sensing.

Resume : Silicon photonics has become a mature integrated-optics technology in the last decade for applications in telecommunications and data communications. Germanium (Ge) is a group IV material compatible with CMOS foundry and interesting for silicon photonics because its direct gap energy corresponds to an absorption band-edge at 1.55 µm wavelength. In addition despite being an indirect band gap material, direct gap-transitions can be used for photonic devices, thanks to the small energy difference between the indirect and direct bandgap energies. The potential of Ge/SiGe quantum wells (QW) has been largely shown recently, with for example demonstrations of electro-absorption and electro-refraction by Quantum Confined Stark effect. Ge/SiGe QW can also be engineered to shift absorption band-edge and thus the operating wavelength of optical modulator based on such structures. In this context, experimental analysis of the material properties of Ge/SiGe QW structures and particularly direct gap optical transitions is of a major importance. We will report room temperature photoluminescence of Ge/SiGe QW structures grown on SiGe graded layer. From the measurements, transition energies in the QW are deduced as a function of the QW design, and compared with simulations. A good agreement between photoluminescence measurements and simulations of the optical transitions in the QW is of a major importance to engineer new Ge/SiGe quantum well structures with innovative functionalities.

Resume : GaP is a promising candidate for the development of highly integrated photonic functions on silicon, because of its quasi lattice-matching with Si and its interesting χ(2) non-linear properties (d14=37pm/V at 1.3 µm for instance). We here present the realization of GaP-based microdisks on Si substrates, and discuss their optical properties.[1] Especially, emphasis is given on a detailed study of the antiphase boundaries (APB) impact on second-order harmonic generation. At first, the typical antiphase domains distribution in GaP/Si epilayers is determined by plan-view Transmission Electron Microscopy (TEM) imaging. From this experimental data, a Fourier-transform analysis combined with a semi-analytic modeling is then used to simulate non-linear optical properties of various GaP/Si epilayers with different average crystal polarities. As a main result, it is found that at a constant average crystal polarity, the size of APDs does not impact the non-linear properties, while the average polarity of the crystal itself is the most important parameter. Finally, it is shown that controlling the APB nucleation would even be interesting for non-linear optical applications. This work is supported by the Labex CominLabs through the "3D Optical Many Cores" project and the Région Bretagne. [1] P.S. Kuo et al Nature Comm., 5 3109 (2013)

Resume : III-V compound semiconductor quantum dots laser is attractive because of its temperature independent operation, low power consumption and high-speed modulation. It is difficult to realize uniform dot size, spacing, and density assembled by conventional methods. We have successfully developed original top-down process using a bio-template and neutral beam etching to actualize GaAs nanopillars (NPs). However, effective functional devices require GaAs quantum nanodisks (QNDs) after regrowth process embedded by AlGaAs matrix material. In this study, we discuss the PL spectra of GaAs QNDs and their original NPs for understanding carrier recombination mechanism. As-etched (NPs), regrowth (QNDs) and MQWs with four QND layers were prepared. PL measurements were performed at 20 K by using an Ar ion laser as excitation source and a photo-multiplier as a detector. PL peak at 1.55 (A), 1.60 (B), and 1.64 (C) eV for as-etched sample were observed. Since the peaks B and C were not observed in MQWs sample, these peaks were due to the quantized levels in QNDs. TEM observation showed that there is a diameter distribution of the QNDs which therefore induced the complex PL peaks, due to different degrees of quantum confinement. For the regrowth sample, the same peaks were also observed. However, the intensity of the peaks from QNDs became larger. This may be due to the decrease of nonradiative recombination at the ND surface by the regrowth process.

Resume : III-V compound semiconductor nanoscale devices, such as quantum dots (QDs) and quantum nanodisks (QNDs) laserdiodes have attracted much attention due to their characteristics. However, it is very challenging to realize a high density and uniform two-dimensional array of QDs. We developed a damage-less top-down dry process to fabricate GaAs QND LEDs by fusion of a bio-template and a neutral beam (NB) etching. The bio-nano-template consists of a high-density, two-dimensional array of cage-shaped proteins called ferritins with encapsulated metal oxide nanoparticles. Ferritins can be functionalized with polyethylene glycol (PEG) to control the distance between them and avoid in-plane wave-function coupling from QNDs. Multiple quantum wells samples of GaAs/AlGaAs were grown by metalorganic vapor phase epitaxy. After the formation of a self-assembled monolayer of ferritin by spin-coating, the protein shell was removed by an oxygen treatment in vacuum. Removal of the surface oxide was performed by hydrogen radical and then chlorine NB etching was performed through the MQWs to form GaAs QNDs. After regrowth of different AlGaAs barrier matrix, temperature dependence of the E-L characteristics was measured between 4 K and 293 K. The E-L intensities from these QND LEDs were found to monotonically decrease, but top-down fabricated QND-LEDs successfully emitted at room temperature.

Resume : GaAs and InGaAs structures based on wafer bonding and epitaxial growth by metal organic chemical vapor deposition techniques are often used in combination with traditional Si microelectronic devices aimed at the enhancement of the performance of the latter. In this work, the kinetics and peculiarities of the MOCVD growth of GaAs and InGaAs structures for the microelectronic device fabrication are studied by lattice kinetic Monte Carlo (LKMC) modeling. The LKMC model operates with the delivery rates of the group III and V precursors toward the growing surface as well as with the rates of atom incorporation into the lattice taking into account the interaction with neighboring lattice atoms up to third nearest neighbors. The model is calibrated with respect to the experimental growth rates of the flat GaAs and InGaAs layers of different orientations. The modeling results enable to describe the peculiarities of the shape formation (faceting) of the GaAs and InGaAs structures in confined geometries as used for the microelectronic device fabrication. These peculiarities are studied as function of the precursor partial pressures in the reactor atmosphere and deposition temperature. Physical mechanisms influencing on the formation of the GaAs and InGaAs structures are also discussed. Obtained results are useful for the elaboration of the technologies for the novel types of microelectronic devices based on III-V epitaxial structures.

Resume : Recent achievements in employing a wafer-scalable strain technology give the prospect of direct bandgap germanium as gain material for the realisation of a laser source for CMOS compatible optical interconnects [1]. A crucial step towards such a laser is the implementation of an optical cavity compatible with micron-sized suspended bridges which are under high strain . First attempts, based on DBR cavities, already resulted in up to 2.5% strain [2,3]. Here, we present design, analysis and realisation of two novel optical cavities, namely a lateral DFB and a corner-cube reflector, respectively. The high quality optical GeOI [4] enabled to reach 3.6% strain as verified by micro-XRD calibrated Raman spectroscopy [5] for structures with integrated cavity. For the corner-cube cavity, photoluminescence spectra reveal a strong modulation due to cavity modes with Q-factors larger than 800 (resolution limit of the measurement) and a mode-spacing of 17nm. FEM-simulations reveal for the DFB and edge cube reflector Q-factors of up to 600 and 4'000, respectively. In conclusion, two high Q-factor cavity designs compatible with our strain-engineering approach are presented, providing a promising component for achieving lasing in tensile-strained direct bandgap Ge. [1] M. Süess et al. Nat. Phot. v7, 488 (2013). [2] Petykiewicz et al., arXiv:1508.01255v1 (2015) [3] A. Gassenq et al, OSA CB_11_1 (2015). [4] V. Reboud et al. Proc. SPIE 936714, 1 (2015). [5] A. Gassenq et al, to be published.

Resume : After many years of development of sub-micrometer diffraction of x-rays, we have recently developed a novel type of scanning probe microscope [1] addressing the parameters strain and lattice orientation, in epitaxial as-grown and deeply buried structures, to a precision unobtainable by any other method. We used this non-destructive model-free technique to access in a direct way strain and lattice orientation of CMOS process fabricated Ge-based microstructures. Being a potential low cost photonic component, such devices are fabricated at the micrometer scale and have very complex geometries, as two-dimensional or three-dimensional structures, leading to non-uniform strain distribution. In this context, the characterization and quantification of locally resolved lattice distortion are relevant for understanding the engineering processes applied to control the device performances. We will present an exhaustive synchrotron x-ray microdiffraction imaging of Ge photonic devices [2]. Different aspect ratios were probed covering a range of dimensions over which these structures may be functional for future light emitter applications. Strain and lattice orientation distributions were imaged in great detail that are inaccessible by any other technique, Δa/a=10-5 and 10-3 degrees respectively. They were extracted by using the strain and orientation calculation software package X-SOCS. The obtained results will be compared with the biaxial strain distribution obtained by lattice parameter-sensitive µ-Raman and µ-photoluminescence measurements. The experimental data will be interpreted with the help of finite element modelling of the strain relaxation dynamics in the investigated structures. In addition, in-situ x-ray microdiffraction measurements were recently conducted to investigate the temperature dependence of strain distribution for the most relevant microstripe. These results will also be presented in this talk.

Resume : For several decades optical interconnects have been envisioned as an approach to overcome the limitations of metal-based CMOS interconnects once a solution for a monolithically integrated laser source is found. Such a laser should offer efficiencies of III-V lasers while also providing full compatibility with CMOS. Hence, a direct bandgap group IV material is highly desired, where GeSn alloys with Sn-concentration > 10% [1] or tensile strained germanium are the most prominent candidates. Here, we present a high-quality optical germanium-on-insulator platform [2] where a temperature-induced small biaxial pre-strain of 0.16% has been uniaxially enhanced up to 3.6% using underetched 1µm thick microbridges. Inherent to the here applied strain enhancement principle [3], cooling below 300K increases the biaxial pre-strain and, hence, the strain in the microbridges up to 5.4% as is deduced from Raman spectroscopy and its correlation with Laue microdiffraction performed at the ESRF facility [4]. Temperature-dependent photoluminescence experiments show a strong increase of the intensity for microbridges with strain above 4 to 4.5 %. This is explained by the thermalization of electrons into the Gamma-valley, hence, revealing the crossover from an indirect to a fundamental direct bandgap semiconductor. [1] S. Wirths et al. Nat.Phot. v9, 88 (2015) [2] V. Reboud et al. Proc. SPIE 936714, 1–6 (2015) [3] M. Süess et al. Nat. Phot. v7, 488 (2013) [4] A. Gassenq et al, to be published

Resume : Recent developments in LEDs allowed them to be used in environmental lighting and have revealed many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. Besides this general lighting application, LEDs are now used in other specific fields such as automotive headlamps, traffic signals, advertising, and camera flashes. However another emerging field of application is in advanced communications technology due to its high switching rates. Thus, the visible light spectrum is currently being used in the Visible Light Communication (VLC) technology, taking advantage of the lighting infrastructure based on white LEDs, enabled by the invention of efficient blue LEDs. In this paper we propose the use of a multilayered pinpin device based on a-SiC:H to work as a photodetector operating in the pertinent range of operation for VLC (375 nm – 780 nm) using as optical sources white LEDs based on phosphor and on a tri-chromatic RGB chip. The photodetector device consists of a p-i'(a-SiC:H)-n/p-i(a-Si:H)-n heterostructure with low conductivity doped layers, sandwiched between two transparent contacts. It works as an optical filter in the visible range with tunable spectral sensitivity dependent on both applied bias and type of steady state optical bias (wavelength, intensity and direction of incidence on the device). Optoelectronic characterization of the device is presented and includes spectral response, transmittance and I-V characteristics, with and without background illumination. Results show that when the device is biased with front optical steady state light of short visible wavelength (400 nm) superimposed with the pulsed light emitted from the optical transmission sources, it exhibits an increased output current in the long range of the spectrum (550-650 nm), and a reduction of the same photocurrent for the short wavelengths (400-500 nm). Additionally, the background illumination from the back side also influences the photocurrent signal that is enhanced in the short wavelength range and strongly reduced for the long wavelengths. Thus the device works as a visible optical filter with controlled wavelength sensitivity through the use of adequate optical biasing light, which enables the possibility of detecting different wavelengths. This feature allows the recognition of the individual components of the tri-chromatic white LED, which enlarges the amount of information transmitted by this type of white LED, when compared to the phosphor based LED. A decoding algorithm for the detection of different optical signals is presented and discussed with an error detection procedure. A capacitive optoelectronic model supports the experimental results and explains the device operation. A numerical simulation will be presented.

Resume : Hyperdoping silicon with chalcogen atoms is a topic of increasing interest due to the strong sub-band gap absorption exhibited by these materials, which can be exploited to develop infrared photodectectors and intermediate band solar cells [1-3]. In our work, tellurium-hyperdoped Si layers have been fabricated by ion implantation followed by either millisecond range flash lamp annealing (FLA) or nanosecond range pulsed-laser melting (PLM). The Rutherford backscattering spectrometry / Channeling (RBS/C) results reveal the high-quality recrystallization of tellurium implanted Si by both FLA and PLM. From the transport measurements, the conductivity increases with increasing tellurium concentration and the high tellurium concentration samples show a finite conductivity if temperature tends to zero. This indicates that the high concentration doping of tellurium induces an insulator-to-metal transition in silicon although tellurium introduces a deep donor in Si. Moreover, the ellipsometry measurements show that the band gap narrows with increasing doping concentration, which could enable silicon-based optoelectronics in the infrared spectral range. [1] Kim, T. G., et al., Appl. Phys. Lett. 88, 241902 (2006) [2] Tabbal, M., et al., Appl. Phys. A 98, 589–594 (2010) [3] Umezu, I., et al., J. Appl. Phys. 113, 213501 (2013)

Resume : The development of room-temperature Si infrared photodetectors, whose range of detection lies on the traditional telecommunication wavelengths around 1300 nm and 1550 nm, is of paramount importance for optical communications, integrated photonics, sensing and medical imaging applications [1]. The typical peak photoresponse of conventional Si photodetectors is between 700 and 900 nm, which is primarily limited by the 1.12 eV-Si band gap. However, such intrinsic material limitation can be overcome by introducing transition metals or chalcogens into the Si band gap at concentrations far above those obtained at equilibrium conditions [1, 2]. This new class of hyperdoped materials with a donor impurity band has been postulated as a viable route to extend the Si photoresponse at the infrared spectral region [3]. In this work, we report on the significant room-temperature photoresponse and performance at the two primary telecommunication wavelengths as exhibited by hyperdoped Si p-n photodiodes fabricated by Se implantation followed by millisecond flash lamp annealing (FLA). The FLA approach in the millisecond range allows for a solid phase epitaxy that has been reported to be superior to liquid-phase epitaxy induced during pulsed laser annealing [2]. The success of our devices is primarily based on the high quality of the developed n-type hyperdoped material, which is single-phase single crystal with high electrical activation, without surface segregation of Se atoms and with an optically flat surface. [1] J. P. Mailoa, A. J. Akey, C. B. Simmons, D. Hutchinson, J. Mathews, J. T. Sullivan, D. Recht, M. T. Winkler, J. S. Williams, J. M. Warrender, P. D. Persans, M. J. Aziz, and T. Buonassisi, Nat. Commun. 5, 3011 (2014). [2] S. Zhou, F. Liu, S. Prucnal, K. Gao, M. Khalid, C. Baehtz, M. Posselt, W. Skorupa, and M. Helm, Sci. Rep. 5, 8329 (2015). [3] I. Umezu, J. M. Warrender, S. Charnvanichborikarn, A. Kohno, J. S. Williams, M. Tabbal, D. G. Papazoglou, X. C.Zhang, and M. J. Aziz, J. Appl. Phys. 113, 213501 (2013).

Resume : In this paper we present a selector based on a multilayer a-SiC:H optical filter that requires appropriate near-ultraviolet steady states optical switches to select the desired wavelengths in the visible range. Spectral response and transmittance measurements are presented and show the feasibility of tailoring the wavelength and bandwidth of a polychromatic mixture of different wavelengths. The selector filter is realized by using a two terminal double pi’n/pin a-SiC:H photodetector. Five visible communication channels are transmitted together, each one with a specific bit sequence. The combined optical signal is analysed by reading out the photocurrent, under near-UV front steady state background. Data show that 25 current levels are detected and correspond to the thirty-two on/off possible states. The proximity of the magnitude of consecutive levels or some noise during the read out process causes occasional errors in the decoded information. To minimize the errors, four parity bit are generated and stored along with the data word. The parity of the word is checked after reading the word to detect and correct the transmitted data. Results show that the background works as a selector in the visible range, shifting the sensor sensitivity and together with the parity check bits allows the identification and decoding of the different input channels. A transmission capability of 60 Kbps using the generated codeword was achieved. The relationship between the optical inputs and the output signal is established and an algorithm to decode the MUX signal presented. Here, parity logic operations and syndrome decoding process are used and checked for errors together. An optoeletronic model gives insight on the system physics.

Resume : In this paper, we focus on the nonlinear property of SiC multilayer devices under UV irradiation to design an optical processor for indoor positioning. The optical processor, for indoor positioning, error detection and correction, is realized using an a-SiC:H double p-i-n photodetector with two UV light biased gates. The relationship between the optical inputs (transmitted data) and the corresponding digital output levels (received data) is established and decoded. Parity logic operations are performed and checked for errors together. The extra bits (parity bits) in the code word provide redundancy that, according to the coding scheme used, will allow the destination to use the decoding process to determine if the communication has introduced errors and to correct them, so that data need not to be retransmitted. The code word is decoded at the destination to retrieve the checked parity logic operations performed. Based on that, we present a promising way to achieve indoor localization using the parity bits and the navigation syndrome. A representation with a 4 bit original string colour message and the transmitted 7 bit string, the encoding and decoding accurate positional information processes and the design of SiC navigation syndrome generators are discussed. The visible multilateration metodh estimates the position of the device by using the strength of the signal received from several, non-collinear transmitters.The location and motion information is found by mapping position and estimates the location areas. Since the indoor position of the LED light source is known from building floor plans and lighting plans, the corresponding indoor position and travel direction of the mobile device can be determined.

Resume : Leveraging the robust fabrication infrastructure of silicon microelectronics, microstructures designed for silicon photonics enjoy advantages over other optical waveguide motifs in terms of scalability and manufacturability. We have developed an analytical detection platform around silicon photonic microring resonators and have utilized this technology for a broad range of chemical and biomolecular detection applications. The major emphasis of this platform has been multiplexed biomarker analysis, and point-of-care diagnostics. Other applications include studies of biochemical complex formation, as well as fundamental studies of polymer growth and partition dynamics using chemically-modified microring resonators.

Resume : Whispering Gallery resonators have a wide field of applications in telecommunication and sensor technology. Here microdisk resonators reach high quality factors and allow a direct integration with common standard silicon semiconductor processes. Due to scattering losses the quality factor is strongly influenced by surface roughness. In this work we present a fully CMOS compatible process for the fabrication of high-Q whispering gallery microdisk resonator based on silicon oxynitride. Dielectric layers are deposited by using plasma enhanced chemical vapor deposition (PECVD) with silane, ammonia and nitrous oxide at a substrate temperature below 400 °C. This enables an integration of optical components in common with CMOS circuits on the same chip. The process parameters are optimized for a reduction of the incorporated hydrogen bonds and reduced surface roughness. Structures are defined by optical lithography with a subsequent etching in buffered hydrofluoric acid. The undercut of the microdisk to prevent thermal and optical coupling to the silicon substrate is realized by isotropic reactive ion etching using sulfur hexafluoride. The quality factor was measured by evanescent field coupling of a tapered optical fiber. Here a quality factor of 5•10^5 was observed for a silicon oxynitride microdisk resonator with a diameter of 80 µm at a wavelength of 1330 nm.

Resume : Ultrafast and highly efficient optical modulators that are based on the Pockels effect are key components of today’s optical communication networks. The highly integrated silicon (Si) photonic technology however cannot exploit the advantages of using the Pockels effect for optical switching: First, silicon does not exhibit any Pockels effect, and second, attempts to integrate nonlinear materials to silicon have been cumbersome. Here, we demonstrate a novel solution to integrate barium titanate (BTO) thin films with strong Pockels coefficients of ~150 pm/V into silicon photonic structures. We will highlight various material properties that are critical for obtaining large Pockels coefficients and show how to control them via molecular beam epitaxy [1]. We then discuss various design and process options of integrating BTO in Si waveguides. Experimental results of passive structures such as waveguides with low losses of <6 dB/cm, ring resonators with quality factors of >20’000 and Mach-Zehnder interferometers will be presented. We will also discuss active, electrically driven nonvolatilely tunable ring resonators with a tunability of 4 µW/nm [2]. Our results represent a major advancement in the field of ultra-low-power silicon photonic switches, and demonstrate the potential of combining materials science with silicon photonics to enable new integrated, optical functionalities. [1] Abel, S. et al. Nat. Commun. 4, 1671 (2013) [2] Abel, S. et al. J. Light. Technol. 34, 01–6 (2016)

Resume : The detection and identification of small amounts biological and chemical targets are important in biotechnology, for the pharmaceutical industry, and for public health and safety. Resonant devices made using the silicon on insulator (SOI) platform are attractive for sensing in the near infrared where silicon is transparent. Because the electric field is strongly localized in most of these devices, a very small amount of material can detected and identified. This presentation will focus on the design, development, and validation of different SOI photonic crystal devices, including 1-D and 2-D microcavities, coupled microcavities, and photonic crystal/microring hybrid devices.

Resume : Biophotonic based sensing or imaging relies often on expensive and bulky equipment. Integrated optics solutions could alleviate both cost and equipment size, by integrating the optical functionality on chip. Even more so, it is beneficial to integrate this optical functionality directly on top of a CMOS chip, that can detect the light and process the information. We have developed a 200 mm CMOS compatible SiN waveguide platform with low losses at visible wavelengths. We have already demonstrated density controlled nanophotonic waveguide gratings for tailored out-coupling of light, and applied this to integrated excitation and detection of fluorescently tagged particles and cells. In addition, we have shown integrated excitation and collection of molecular fluorescence. In this talk we will discuss the current component library and the applications that are envisioned.

Resume : With the increasing demand of data, current chip-scale communication systems suffer rate limitations and power consumption. In this context, Silicon photonics has emerged as an alternative for data transmission by replacing classical copper interconnects with silicon waveguides. Silicon is now considered as an excellent candidate for the development of integrated optical functionalities including waveguiding structures, modulators, switches… One of the main challenges of silicon photonics is to reduce the power consumption and the swing voltage of the optical silicon modulators. However, silicon is a centrosymmetric crystal, vanishing the second order nonlinear effect i.e. Pockels effect which is intrinsically a high speed effect. To overcome this limitation, mechanical stresses on silicon to break the crystal symmetry can be used depositing a strained overlayer. In this work, we have studied the effect of the stress layer in the modulation characteristics based on Mach-Zehnder interferometers. The deposition of the stress layer and its optimization to induce the maximum effect will be presented.

Resume : The mid-infrared (mid-IR) spectral region is of great interest to many areas of science and technology as it contains two important transparency windows (3–5 μm and 8–13 μm) of the Earth’s atmosphere and strong characteristic vibrational transitions displayed by a large number of molecules. Praseodymium ions (Pr3 ) feature characteristic transitions in the mid-IR and transmission range of chalcogenides based materials spans a large part of the mid-IR. The combination of efficient waveguiding properties with mid-IR light emitters would therefore be a key enabler of the development of mid-IR sensors-on-a-chip for health, security and environmental applications. RF magnetron sputtering is used to deposit a Pr3 -doped chalcogenides guiding layer based on the quaternary system composed of Ga, Ge, Sb and Se atoms on different cladding layers. The optical design of integrated ridge waveguides for single-mode propagation at mid-IR wavelengths is presented. Then, the fabrication process of these structures using photolithography and RIE/ICP dry etching is described. Single-mode propagation of mid-IR laser light is observed in ridge structures by optical near field imaging. Furthermore, Pr3 guided photoluminescence in the mid-IR around 2.5 µm and 4.5 µm is demonstrated at room temperature using co-propagating pumping around 1.55 µm and investigated as a function of films annealing.

Resume : Carbon nanotubes (CNT) exhibit outstanding optical, electrical and mechanical properties. Thanks to advances in material quality and separation methods, an increased attention has been drawn to the implementation of CNT-based photonic devices compatible with silicon technology. Light-emitting devices based on electro- and photo-luminescent properties of semiconducting single-wall carbon nanotubes (s-SWCNT) have been implemented. However, none of these results were demonstrated in the telecommunications-relevant range around 1.55 µm. Enrichment in s-SWCNTs with emission wavelengths tunable to the dominant telecommunications spectral window is achieved by controlling the parameters of SWCNT synthesis and dispersion in polyfluorene-based polymers. Organic films containing selected chiralities of s-SWCNT are spin-coated onto Si substrates and optically characterized (refractive index, absorption and photoluminescence). Ridge waveguides are then fabricated using processing steps compatible with CMOS technology and exhibit single-mode propagation at 1.55 µm. Using these waveguides, guided photoluminescence (PL) from s-SWCNT is demonstrated for the first time around 1.55 µm. Alternatively to previous approaches, s-SWCNT are incorporated in the core layer of the waveguiding structure to benefit from an increased coupling efficiency of s-SWCNT PL with the waveguide optical mode. These findings underscore the utility of s-SWCNT for the development of silicon photonics around 1.55 µm.

Resume : In optical communication systems, optical nonreciprocal devices are indispensable in protecting active photonic devices from unwanted reflected light. An optical isolator employing a nonreciprocal phase shift is attractive because the device utilizes transverse-magnetic (TM) modes only so that there is no need for phase matching. The nonreciprocal phase shift occurs in TM modes that travel in magneto-optic waveguides in which magnetization is aligned transverse to the light propagation direction in the film plane. By using the nonreciprocal phase shift, an optical isolator that makes use of a nonreciprocal guided-radiation mode conversion can be realized. A magneto-optic waveguide in the optical isolator has an air / Si / magnetic garnet structure. The nonreciprocal phase shift in the magneto-optic waveguide was calculated at a wavelength of 1.55 micron. The optical isolator employing the nonreciprocal guided-radiation mode conversion was designed at 1.55 micron. Then, the temperature dependence of the optical isolator was investigated.

Resume : This paper investigates the electrical characteristics of a nanoscale SOI tri-gate n-channel fin field-effect transistor (FinFET) structure with two different gate lengths using zirconium dioxide (ZrO2) as a gate dielectric material. The numerical device simulator ATLAS™ is used to simulate the structure in three dimensions with different models including the quantum effects. The drain current, transconductance, threshold voltage, subthreshold swing, leakage current, drain induced barrier lowering, and on/off current ratio are analyzed in the various biasing configuration. In addition, the fin-thickness and gate work function effects on the main electrical parameters of the FinFET device are investigated. Increasing of fin-thickness tends to exhibit degraded performance of some basic parameters, such as subthreshold swing and leakage current. Therefore, the transistor with the larger channel and the larger gate are the most immune to SCEs. In addition, in the strong inversion region quantum effects reduce the drain current, which is always smaller than classical model because of energy quantization.

Resume : Investigation of boronitrides has begun as early as the 1960ties [1]. Since then, boronitrides of alkali metals, alkaline earth metals, and lanthanides have been reported [2-4]. One interesting aspect in boronitride chemistry is the versatility of the structural building units, ranging from N3-, BNx-, BN23-, BN36-, B2N48- to B3N69- and even combinations thereof. The title compound, SrBa8(BN2)6, was first reported by Somer et al. together with its isostructural analogous, EuBa8(BN2)6 [5]. In this study, we report on the new red-emitting compound SrBa8(BN2)6:Pr3+. In order to gain insight into fundamental photoluminescence (PL) processes depending on the structural elements present in the material, PL spectra, reflectance spectra, and decay constants were recorded. References [1] J. Gobeau and W. Anselment, Z. Anorg. Allg. Chem., 310 (1961) 248-260 [2] C. Koz, S. Acar, Y. Prots, P. Höhn and M. Somer, Z. Anorg. Allg. Chem., 640 (2) (2014) 279-285 [3] S. A. Kulinich, L. G. Sevast’yanova, G. N. Bondarenko and K. P. Burdina, Russ. J. Gen. Chem, 69 (4) (1999) 530-533 [4] B. Blaschkowski, H. Jing and H.-J. Meyer, Angew. Chem. Int. Ed. 41 (2002) 3322-3336 [5] S. S. Öztürk, I. Kokal and M. Somer, Z. Kristallogr. NCS, 220 (2005) 303-304

Resume : Synthesized-CdSe nanoparticles were deposited by using spin coating method onto porous GaAs substrate elaborated by an electrochemical process. Surface morphology and surface roughness of the deposited CdSe layers was investigated by scanning electron microscopy (SEM) and Atomic Force Microscopy (AFM). SEM imaging shows an inhomegenity distribution of CdSe nanoparticles; which can be related to the non uniformity of the pores on the GaAs ‘surface. In addition, the CdSe was penetrated deeply in the porous structure down to the bottom and reaching the interface GaAs/porous GaAs. AFM exhibits that the CdSe layer deposited on porous Gas substrate has more roughness. X- ray diffraction (XRD) technique proves the incorporation of CdSe nanoparticles on the surface states. It was also observed that the reflectivity decreased due to the appearance of roughness which is in agreement with the SEM and AFM analysis. Also, the photoluminescence (PL) spectroscopy exhibits a new intense peak centered at 2.08 eV related to CdSe nanoparticles about 2nm of diameter which was determined by using effective mass approximation model from effective band gap. Keywords: Porous GaAs, Cadmium selenium (CdSe), SEM, UV-Visible.AFM, Pl, XRD

Resume : In this work, we investigate the thermal oxidation effect on optical and thermal properties of meso-porous silicon (meso-PS) layers using photoluminescence (PL) and photothermal deflection techniques (PDS, PTD). Samples have been successfully prepared by electrochemical anodization process. After a pre-oxidation for 1h 30 min at 300°C, layers are thermally oxidized in dry oxygen at different temperatures (800, 1000°C) and durations. PL measurements show that the annealed layers have comparable spectra with a peak position focused on 2.1 eV. This behavior indicates the formation of luminescent silicon (Si) nanocrystallites with comparable average sizes. From the effective mass theory, the diameter of those nanocrystallites was estimated to be around 2.2 nm. Another estimation of the mean size of the Si nanocrystallites obtained from the evolution of the thermal conductivity of the meso-PS layers based on photothermal deflection technique (PTD) data was close to the values obtained from the PL results. Photothermal deflection spectroscopy (PDS) measurements show that the thermal oxidation affects the absorption edge of the Si substrate. The optical band gap energy of the started substrates determined from the Tauc’s relation is observed to increase with the thermal temperature and duration.

Resume : In this work, we investigate the effects of growth conditions on the optical properties of bulk AlxGa1-xN layers using photoluminescence (PL), time-resolved photoluminescence (TRPL), and photoreflectance (PR) techniques. The studied samples were grown by atmospheric-pressure metal organic vapor phase epitaxy (AP-MOVPE) on GaN templates. Our results show that the Al solid composition (x) of the studied AlxGa1-xN layers is related not only to the trimethylaluminum (TMA) flow rate, but also to the trimethylgallium (TMG) and NH3 flow rates. It is found that the increase of the Al solid composition, via increasing TMA or NH3 flow rates, deteriorates the optical quality of the AlxGa1-xN layers. In contrast, when the TMG flow rate is reduced, the optical quality is improved and the Al composition is increased.

Resume : Micro-displays based on an array of micro-sized light emitting diodes (µLEDs) are a promising technology for a wide range of applications. Reducing the size of displays while maintaining a high resolution bring the need for very small µLEDs patterned in a 2-Dimensionnal array. In this paper we investigate the effect of size reduction on light emission and efficiency on InGaN/GaN LED devices ranging from 500*500 µm² to 5*5 µm². Electroluminescent characterizations together with IVL measurements are conducted to study the homogeneity of light emission and correlate with efficiency measurements. The results show a strong size-dependent efficiency. Smaller LEDs exhibit lower efficiency. The study of the homogeneity of light emission is shown to depend on current densities. At low current densities, light emission is homogeneous across the surface of the LED. With increasing current densities, different emission areas appear. Depending on the size of the LEDs, these emission areas vary. Focused-Ion-Beam characterizations are conducted to investigate the phenomenon and correlate with fabrication process. We will give and discuss hypothesis for these effects. Further investigations are conducted to fully apprehend the influence of size on the efficiency and light emission homogeneity of µLEDs. These results are important to understand the properties of µLED arrays, since such device would allow the fabrication of very-high brightness emissive micro-displays. ACKNOWLEDGMENTS This work was supported by the French National Research Agency (ANR) through Carnot funding

Resume : An effective and reproducible method for the deposition of thin films has been presented and used to manufacturing nanoporous zeolite (NaA) on p-Si by spin coating method which supports the formation of nanoporous zeolite (NaA) with different time deposition. The nanoporous zeolite (NaA) films cover partially the pores of the p-Si which is self-organized. Then it were modeled as a mixture of zeolite (NaA) ,void, Si. The effect of different time deposition was systematically studied by atomic force microscopy (AFM), scanning Electron microscopy (SEM), Raman spectroscopy and X-ray diffraction (XRD). The optical constants (n and k as a function of wavelength) of the films were obtained by using the spectroscopic ellipsometry (SE) in the UV-vis-NIR regions. Fick law was introduced to explain diffusion phenomenon zeolite (NaA) in p-Si .A very bright photoluminescence (PL) was obtained with a strong dependence with different time deposition.

Resume : Amorphous silicon oxicarbide thin films a-SiOC(:H) were deposited by RF-magnetron sputtering using silicon or silicon carbide target in argon/methane/oxygen flow. Deposition temperature was 200 C. The effect of target material (Si vs SiC), discharge power and composition of working gas mixture were studied. Interatomic bonding and light emission properties were analyzed by FTIR, Raman scattering and photoluminescence spectroscopy. No Si-C bonds were found in low density a-SiOC:H films deposited using silicon target. The structure of such material is composed by hydrogenated carbon domains incorporated in amorphous silica network. It is demonstrated that increase of segregated carbon enhances broad band visible photoluminescence. Using of Si-C target allows introducing of Si-C bonds in SiOC amorphous network that improve mechanical and chemical durability of the films. Comparative analyze of structural and luminescent properties are discussed in terms of structural homogeneity of interatomic bondings and carbon segregation.

Resume : The incorporation of different functional optoelectronic elements on a single chip enables performance progress, which can overcome the downsizing limit in silicon technology. For example, the use of Ge instead of Si as a basic material in nanoelectronics would enable faster chips containing smaller transistors. In this work, we present the development, optimization and fabrication of high-mobility channel materials based on Ge using plasma-enhanced chemical vapour deposition of Ge on insulator and its recrystallization via millisecond range lateral explosive epitaxy. It is shown that the mechanism of explosive recrystallization of Ge layer (solid vs liquid phase) can be controlled by Sn co-doping and/or varying the annealing time. The influence of the explosive recrystallization and the Sn co-doping on the dopant activation efficiency and the carrier mobility in the GeOI after millisecond range flash lamp annealing is discussed.

Resume : In recent years, photonic crystal (PhC) slabs gained strong attention due to their ability to systematically control light-matter interaction enabling the design of novel optoelectronic devices. Such PhC slabs provide the possibility to strongly enhance an external field near the surface when designed properly. Thus, by utilizing the PhC resonances, applications like highly efficient optical sensors and spectral conversion devices could be realized. In this study, we detect the near-field enhancement for large-area, quasi-2D PhC slabs based on silicon. A thin layer of lead sulfide (PbS) quantum dots with a mean core diameter of 6 nm and a photoluminescence emission peak at 1377 nm was deposited from liquid dispersion on the PhC surface via convective assembly [1]. In order to map the near-field enhancement, we measure the fluorescence of the quantum dots on the PhC surface when coupling to the external light field. In the experimental setup, angle and wavelength of the incident light can be tuned to excite specific modes. At the same time, we integrate over all scattering angles of the resulting signal using an integrating sphere. We observe a strongly modified, wavelength and angle dependent fluorescence spectrum if a PhC is present and compare the results to high-accuracy finite element scattering simulations [2] and band structure computations. [1] Kraus et al. Nature Nanotech. 2, 570, (2007) [2] Becker, C. et al. Sci. Rep. 4, 5886 (2014)

Resume : Recently, ultraviolet (UV) thin film photodetectors (PDs) have received much consideration in different field of research due to their applications environmental monitoring, optical communications and large-area displays. Optimization of photodetectors including new morphological aspects is indispensible to improve the thin film photodetector performance. In this context, this paper presents a numerical investigation including new interface grating morphology effects in order to optimize the photodetector performance and design parameters. In the present work, the impact of grating designs on the device behavior is studied using optical and electrical modeling and an optimized design is proposed to improve the UV absorbance of the photodetector. The specific photodetector studied is based on a Si/TiO2 structure, though qualitative findings are applicable to any thin film photodetector application. Si/TiO2 PD with optimized triangular grating exhibits an enhancement over conventional planar PDs. The purpose of this work is to find an optimal diffraction grating structure that would help in obtaining high optical and electrical performances.

Resume : Silicon nanowires (SiNWs) can be successfully employed as substrates in laser desorption/ionization mass spectrometry (LDI-MS) applications [1]. Their importance resides in good sensitivity for the analysis of small analytes, thanks to UV absorption properties and high surface area [1]. As compared to conventional organic matrixes, the use of SiNWs allow reducing the background interference below 1000 m/z, at low laser fluence. Here, we report on SiNWs prepared by a maskless wet-etching technique, assisted by the deposition of an ultrathin gold (or silver) film on a Si substrate [2] as LDI-MS platforms. We found that the metal catalyst can improve the performance of the proposed substrates, especially when Ag is used. Moreover, the additional functionalization of SiNWs with metal (Ag, Au) nanoparticles prepared by pulsed laser deposition allow the further enhancement of detection capability towards specific compounds (e.g. fatty acids). Real samples, after proper pretreatment, were also investigated through this approach. The obtained MS results are discussed also in terms of complementary material characterization. Project “Nanomaterials & laser ionization mass spectrometry: a new bio-analytical approach” FIRB Futuro in Ricerca 2008 cod. RBFR088SW7 is acknowledged. [1] M. Dupré et al., Anal. Chem. 84 (2012) 10637. [2] A. Irrera et al., Nanotechnology 23 (2012) 075204. [3] N. Cioffi et al., Spie Newsroom (2015) 10.1117/2.1201509.006086.

Resume : Aluminum nitride (AlN) can be used for nonlinear light conversion into the ultraviolet frequency region due to its large transparency window extending down to 200 nm and reportedly large nonlinear coefficients. These nonlinear coefficients were reported from very early AlN crystals and films. Thus, these published values significantly varied due to insufficient optical quality of the investigated crystals. In recent years, significant progress has been made in the growth of larger, good optical quality crystals. We report on measurements of the optical nonlinear coefficient d33 in such bulk AlN single crystals. The nonlinear coefficient was determined by the Maker Fringe method, i.e., by rotating the sample around an axis perpendicular to the incoming laser beam at 1.03 µm wavelength and measuring the generated second harmonic power. A quartz plate was used as a reference. The samples were m-plane (11 ̅00) single crystalline wafers, cut out from a single-crystal AlN boule grown in the -c-direction <000 ̅1>. The crystal was grown by physical vapor transport from a solid AlN source and a nitrogen atmosphere. The crystals obtained from this process had dislocation densities around 10^3/cm^2, with x-ray ω-rocking curves ranging from 18 to 30 arc sec. The samples had the optical (c-) axis <0001> parallel to the wafer surface.

Resume : One-dimensional photonic crystal coated from a mixture of an organic compound (HMDSO) and oxygen (O2) elaborated by PECVD, with changing the flow rate ratio of gazes is studied. The deposition processes of layers is optimized to obtain high and low refractive indexes layers of a good quality giving a photonic crystal with well defined photonic band gap extending in the near IR wavelength range. This structure offers the possibility of potential applications in the field of telecommunication and optoelectronics.

Resume : The monolithic integration of GaP grown by MBE on Si is studied here for photonic applications. The influence of the initial starting Si surface on the quality of the heteroepitaxial GaP layer is first evidenced by cross-sectional transmission electron microscopy (TEM) using samples grown on freshly prepared Si substrates and homoepitaxial Si buffer layers.[1] The relationship between the emergence of antiphase boundaries and the appearing roughness is then demonstrated, with atomic force microscopy, scanning tunneling microscopy and TEM. Especially, emerging antiphase boundaries are found to be faceted at the surface. Finally, surface energies of both GaP and Si are computed together with III-V/Si interfacial energies using first-principles calculations. The three dimensional growth mode observed is then discussed in terms of surface/interface energies. This work is supported by the French National Research Agency project ANTIPODE (Grant no. 14-CE26-0014-01) and Région Bretagne. The ab initio simulations have been performed on HPC resources of CINES under the allocation 2016-[x2016096724] made by GENCI (Grand Equipement National de Calcul Intensif). [1] Y. Ping Wang et al., Appl. Phys. Lett. 107, 191603 (2015).

Resume : We have theoretically studied optical properties of p-doped GaNAsBi/GaAs Single Quantum Well in order to reach the 1.55µm telecommunication wavelength. The calculation are carried out by solving selfconsistently the band (16×16) Kane Hamiltonien combined with the Poisson equation for the hole charge density. We have investigated the effect of p doping density in the well on the subband energies, potential Fermi level and the confining hole density distribution for specific couple (well width Lw,Bi composition y), with respect of confinement conditions. The increase of doping density blueshifts the fundamental transition. Furthermore, the case of doped barrier has been discussed. Based on these results, potential applications in long wavelength range are proposed.

Resume : Linker molecules with two functional groups such as 3-mercaptopropyltrimethoxysilane (MPTMS) are generally used to immobilize DNA or proteins as biochemical receptors at the surface of sensing devices. This silanization of silicon surfaces is well established, as is the reaction of the thiol with gold. However, due to the outstanding chemical and mechanical properties, and the transparency in the wavelength region of 200-5000 nm, sapphire has emerged as a commonly applied material in optical device technology[1]. Yet, little is known on the actual surface structure of bifunctional linkers at sapphire[2]. In order to optimize the grafting procedure for biochemical receptors, the linker reaction should therefore be unambiguously elucidated. In this study, we have therefore determined the orientation of MPTMS molecules attached to the surface of crystalline sapphire (0001) via contact angle measurements, infrared reflection absorption spectroscopy (IRRAS), peak force tapping atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). Additionally, sapphire substrates comprising microfabricated structures of silicon dioxide and gold were used for the direct comparison of adhesion forces determined by peak force tapping mode using a dodecanethiol modification. [1] Takahashi, H. et al., Applied Surface Science, 2012, 262, 129-133 [2] Narita, A. et al., Applied Surface Science, 2012, 258, 2034-2037

Resume : Silicon technology remains dominant in the fabrication of photovoltaic devices (PV). However, to remain competitive, it’s important to reduce the losses of the solar cells based on this technology such as surface reflections. There are several approaches to reduce these losses as the use of suitable antireflection layer (AR). In particular, porous silicon (PS) has been acting as an AR layer thanks to its trapping properties of light. But, porous silicon is not stable in ambient conditions [5]. In particular, PS surface is subjected to an atmospheric oxidation and an appearance of dangling bonds leading to a deterioration of PS properties specially the minority carrier lifetime and the photoluminescence signal. For these reasons, the passivation of the porous silicon is an primordial step in order to keep high silicon solar cells efficiencies. In this work, we demonstrate the effectiveness of ultrathin WO3 film for porous silicon surface passivation. The level of surface passivation is determined by means of photoconductance and FTIR analysis. Fourier Transform Infrared Spectroscopy analysis shows a partial disappearance of peaks due to hydrogenated silicon or hydroxylated silicon oxide and the appearance of new or weakly intense bands that can be ascribed to O-W-O and W=O bridging bounds. We noticed that PS/WO3 samples presents a continuous increase of the effective minority carrier as a function of the immersion time. This is attributed to a best decoration of PS surface by WO3 nanoplatelets and a decrease of surface recombination velocity. We noticed also a significant decrease in the reflectivity of WO3/PS samples as compared to untreated silicon substrates. All these features confirm the benefits of using WO3/PS passivation/antireflection coating for solar cell application.

Resume : The need for ultra-sensitive photodetector has emerged with development of quantum communications and 3D imaging, etc. Single photon avalanche diodes (SPADs) are the typical photodetectors which are sensitive enough to detect a single photon by avalanche effect above breakdown voltage. Especially, silicon SPADs can enable quantum communication in free space by 500nm wavelength light detection. However, even though silicon SPADs have been researched a lot until these days, they have a few drawbacks including high dark count rate and high dead time. In this presentation, we will report the enhancement of dark count rate and dead time by using 2-dimensional transition metal dichalcogenides (TMDC) due to low carrier concentration and low trap density. For showing the feasibility of the thin single photon avalanche diodes, we simulated the photo-response of the silicon p-n junction photodiode with thickness variation at low illumination and compared with the heterojunction of 2D dichalcogenides. We observed the sensitivity to the photons becomes higher with thickness thinning, indicating the possibility of single photo detector made of 2D dichalcogenides.

Resume : The growth methods of monoisotope Si and related materials, and their characteristics are intensively studied in the last decade [1]. Here, the monocrystalline materials of semiconductor quality are of great interest. The ability to develop the methods for the growth of silicon materials with the specifically designed isotopic and impurity content will open novel opportunities for their application: isotope superlattices, semiconductor lasers, etc. One of the most promising areas, where such materials are in demand relates with the quantum computers [2]. In this presentation we will show the ability to grow epitaxial Si, Si1-XGeX and Ge layers of monoisotope content. The high quality 30Si and 74Ge layers with the isotope content of more than 99.9% will be demonstrated. Such kind of materials was grown by means of molecular-beam epitaxy with the sublimated crystalline 30Si and 28Si sources, and / or 74GeH4 gas source. The results of SIMS and Raman spectroscopy studies carried out for these materials show high isotopic purity of 30Si, 28Si, 74Ge and 30Si1-X74GeX layers and their structural perfection. Moreover, the layers that were additionally doped with Er demonstrate intense photoluminescence related with the rare earth impurity. The peculiarities of Er related luminescence in the monoisotope 30Si, 28Si, and 30Si1-X74GeX epitaxial layers are discussed. [1] K.M. Itoh, H. Watanabe. MRS Commun., 4, 143 (2014). [2] P.T. Greenland, S.A. Lynch, A.F.G. van der Meer. Nature, 465, 1057 (2010).

Resume : GaAsPN grown on GaP is an attractive and promising material in view of its use for high efficiencies tandem solar cells on silicon substrates. GaAsPN displays a strong absorption around 1.8-1.9 eV, and efficient photoluminescence at room temperature suitable for the elaboration of multijonction solar cell. However the degradation of the crystalline quality; lattice order of the crystal; and change in the physical properties in mainly linked to N content. In fact, post-growth and rapid thermal annealing (RTA) could be an effective way to limit these effects and improve the optical properties of GaPN-based alloys. To this aim ,we have investigated the optical absorption and thermal properties of GaAsPN absorbers by means of optical absorption spectroscopy and photo-thermal deflection spectroscopy (PDS). The influence of growth conditions and post-growth annealing on optical and thermal parameters is considered. The results are promissing revealing that As modifies the optical properties of GaAsPN with a maximum absorption coefficient of 38,000 cm-1 Indeed, using PDS technique, a significant improvement of optical absorption and thermal conductivity after annealing temperature is shown with the best thermal conductivity around 4 W/mK.

Resume : Intensive researches are currently focused on the miniaturization of devices and on the combination of photonics and electronics in the same platform, in order to decrease the power consumption and to create novel functionalities. In this context, the hybrid integration of oxides on silicon is promising to bring other properties (such as multiferroicity or piezoelectricity) that can be combined and tuned at the nanoscale to develop new devices. However, such integration induces scientific and technological challenges to overcome. The aim of the project is to develop innovative silicon photonic devices by integrating complex epitaxial oxide thin films on silicon and to optimize their physical properties. This work is mainly focused on the optimization of the materials including the crystalline quality, the control of strain fields and the interfaces between oxide and silicon. The experimental study includes the growth of oxide layers on silicon and sapphire substrates by pulsed laser deposition and their characterization by several complementary techniques, such as X ray diffraction, AFM-SEM microscopies, and Raman spectroscopy. Furthermore, the first fabrication and characterization of optical waveguides will be presented and discussed.

Resume : Grating couplers have been widely used for coupling light between photonic chips and optical fibers. Quantum-optics and bio-optics experiments often require coupling light to a microscope system, resulting in an increasing need for good coupling between photonics chips, serving as a microbench for quantum-optics or bio-optics experiments, and microscope systems. In this work, we propose an ultra-compact silicon nitride grating coupler optimized for coupling from a chip single-photon source. The goal is to maximize the coupling efficiency from an optical mode in a suspended waveguide to a microscopy system while maintaining compactness. 3D-FDTD simulations show that up to 80% of the light @ 632.8 nm can be coupled upwards using a grating of only 4x2 um2. The grating structure has been fabricated and characterized. The measured and simulated results show good agreement. As a demonstrator, we embedded one layer of patterned colloidal quantum dots into the suspended silicon nitride waveguide. The emission from the quantum dots coupled to the waveguide mode can be detected by a microscope-based PL setup with the help of this kind of ultra-compact grating coupler.

Resume : Titanium Oxide (TiO2) is a versatile material that has applications in various fields, such as photocatalysis (anatase form) and fabrication of passive electrical (capacitors) and optical (waveguides) devices, among others. We already demonstrated the deposition of partially crystalline TiO2 (anatase) layers by PECVD in O2/TTIP (Titanium tetraisopropoxide) diffusion plasma generated by a RF-ICP source (3 mTorr, 400 W) at 130°C. Such films exhibit high optical index (2.2@633 nm) and permittivity (90@1MHz), but are columnar. To improve the morphology of titanium based oxide layers and increase their bandgap, we introduced HMDSO in the plasma to produce TiSiO layers. Introduction of Si allows to adjust the optical index from 2.2 to 1.46 and the permittivity from 90 to 4.6. To decrease the thermal budget during deposition and obtain a process compatible with sensitive substrates, the plasma source was operated in pulsed mode. The influence of pulse frequency (0.25-1 kHz) and duty cycle (10-100%) on the substrate temperature and film properties are presented here for both TiO2 and TiSiO layers. In both cases, a decrease of the deposition temperature from 130°C to 40°C is evidenced. Even at 40°C, anatase domains crystallise in the TiO2 films. However, the layers become porous which yields a decrease of the optical index (down to 1.8). In the case of TiSiO layers, plasma pulsing has no significant effect on the film composition whereas the optical properties are only slightly changed

Resume : Hybrid structures are needed to fully exploit the great advantages of Si photonics and different approaches have been addressed where Si devices are bonded to different materials and nanostructures. Here we experimentally study the use of semiconductor carbon nanotubes for emission in the 1300 nm wavelength range to functionalize Si photonic structures in view of optoelectronic applications. The Si microrings are fully characterized by near field forward resonant scattering with 100 nm resolution. We show that both TE and TM modes can be addressed on the top of the microrings in a vectorial imaging of the in-plane polarization components. We coupled the Si microresonators with selected carbon nanotubes for high photoluminescence emission. Coupling of the nanotubes with the evanescent tails in air of the electric field localized in the photonic modes of the microresonators is demonstrated by sharp resonances overimposed to the nanotube emission bands. By mapping the Si and the nanotubes emission we demonstrate that strong enhancement of the nanotubes photoluminescence can be achieved both in the photonic modes of microdisks and slot microrings, whenever the spatial overlap between nanoemitters and photonic modes is fulfilled.

Resume : The successful integration of new, 3D nano-architectures into devices such as sensors, solarcells, light emitting diodes (LEDs) a.o. on a silicon (Si) platform requires new approaches towards fabrication and characterization. The present paper will show device concepts relying on Si nanowires (NWs) or inverted, cone-shaped, 1D Si structures (SiNCs) which permit the concentration and confinement of visible (VIS) and near infrared (NIR) light in whispering gallery modes (WGMs). Fabrication concepts based on nano-lithography and dry etching and optical property optimization based on numerical simulations (finite difference time domain - FDTD) will be presented. Individual as well as ensembles of these 1D nano-structures will be integrated in pn-junction solar cells (all-inorganic or organic-inorganic hybrids) and optical sensors. Design rules for optimized absorption or light emission (VIS-NIR) will be derived. Moreover, novel carrier selective, nano-material based contacting schemes will be presented. Among those, composites containing silver nanowires and graphene are demonstrated. Materials and device characterization will rely on advanced correlated electron microscopy and optical spectroscopy (CORMIC) containing electron beam induced current (EBIC) measurements, I-V characterization with and without illumination (with tunable power and wavelength) inside a scanning electron microscope (SEM), cathode-, photo- luminescence as well as in-SEM micro-Raman spectroscopy.

Resume : Silicon nanowires (NWs) are attracting the interest of the scientific community as building blocks for a wide range of future nanoscaled devices. We demonstrate the synthesis of NWs by a cheap, fast and maskless approach compatible with Si technology, using metal-assisted chemical etching of Si substrates catalyzed by thin metallic layer. NWs obtained by this method have tunable nanometer-size diameter, suitable to observe quantum confinement effects, indeed a bright room temperature PL is reported. The realization of Si NWs-based light emitting devices has been demonstrated, showing an efficient room temperature electroluminescence emission at low voltage. We fabricated a low-cost multiwavelength light source working at room temperature, achieved combining Si NWs and carbon nanotubes (CNT). The NW/CNT hybrid system exhibits a tunable emission both in the visible range, due to Si NWs, and in the IR range from CNT, and the conditions leading to the prevalence of the visible or the IR signal have been identified. The decoration of NWs with silver nanoparticles by pulsed laser ablation technique is presented. We demonstrated that the union between the huge surface-to-volume ratio of the Si NWs material and the plasmonic properties of silver nanoparticles unveils advantageous for the use of this unconventional 3D material for ultrasensitive Surface Enhanced Raman Scattering applications with respect to a standard substrate.

Resume : The inorganic-organic interface of hybrid solar cells needs to be well passivated, especially if nanowires with a high surface area are implemented to enhance light absorption.[1] The silicon nanowires have been prepared by metal assisted chemical etching (MACE) of crystalline silicon wafer.[2] The etching procedure leads to an increase of the defect density on the nanowire surface. Surface defects provide active recombination centers in the band gap of silicon and therefore reduce the amount of charge carriers that could be harvested.[3] Electropolishing procedures minimize the density of surface defects and can further modify the morphology of the silicon nanowires. The reduction of the surface defect density was directly monitored by in-situ photoluminescence measurements. Furthermore, different molecules were grafted onto the surface of the silicon nanowires to preserve the enhanced surface properties, which was investigated by infrared spectroscopy and photoluminescence measurements. [1] Jeong, H.; Song, H.; Pak, Y.; Kwon, I. K.; Jo, K.; Lee, H.; Jung, G. Y.; Adv. Mater. 2014, 26, 3445-3450 [2] Huang, Z.; Fang, H.; Zhu, J.; Adv. Mater. 2007, 19, 744-748 [3] Timoshenko, V. Y.; Petrenko, A. B.; Stolyarov, M. N.; Dittrich, Th.; Fuessel, W.; Rappich, J.; J. Appl. Phys. 1999, 85(8), 4171-4175

Resume : The design and development of innovative architectures for energy conversion devices is at the forefront of current research efforts to drive us towards a sustainable future. However, issues related to the cost, efficiency and reliability of current technologies are still severely limiting their overtake of the standard designs. Thanks to their excellent light trapping properties, the use of ordered nanostructures in silicon is expected to overcome these limitations and push the advancement of the alternative technologies. Moreover, self-assembling of Block CoPolymers (BCP) has been recognized as a promising and cost-effective approach to fabricate silicon nanostructures such as nanodots, nanowires or nanoholes (NHs). Recently an array of NHs fabricated by BCP, 20 nm in diameter, 6×10^10cm-2 dense and ordered in a hexagonal configuration has been integrated in complete solar cells exhibiting photovolatic properties thus showing promising results for this easy and low cost approach to be applied in the next generation of solar cells [R. A. Puglisi, Journal of Nanomaterials, Volume 2015 (2015), Article ID 586458]. We now present results of a study performed on NHs integrated into solar cells, where different passivation processes and contact design and materials have been investigated. It is found that the optimized SiNHs based solar cells, present short circuit current as high as 8.7mA/cm2 under 1Sun of Solar irradiation.

Resume : Silicon nanocrystals exhibit downshifting behavior in combination with the potential of efficiently producing multiple electronic charges at the expense of one high-energy photon (carrier multiplication). As a result, two major losses regarding the photon-to-electron conversion of high-quality solar cells (thermalization losses and front surface recombination) could be surpassed: silicon NC based spectral conversion layers are within reach. Or not? The crucial hurdle turns out to be the emission efficiency of the quantum confined particles. In this approach we 1) quantify the system requirements for Si NC based spectral conversion layers by experiment and simulation and 2) perform thorough spectroscopic investigations on high-quality solid-state dispersions of Si NCs to fundamentally address the emission efficiency limit and optimize the production. As a result we are able to reach the highest emission efficiency values ever reported for solid state dispersions of Si NCs. With that in mind, we discuss the application perspective of solar shapers based on Si NCs-in-SiO2 layers.

Resume : Quantum confinement effects (QC) have been proved to lead to light emission of nanostructured silicon (Si) materials, in the perspective of Si-based photonic devices. In this frame, we report on the light emitting performance of two types of Si nanostructures, namely Si nanocrystals (SiNCs) synthesized via Pulsed Laser Deposition (PLD) and Si nanowires (SiNWs) synthesized via Inductively Coupled Plasma (ICP). The optical properties of both nanostructures, characterized via photoluminescence measurements, were associated to the structural ones, performed via Transmission Electron Microscopy (TEM) related techniques. Indeed, High Resolution and Energy Filtered TEM revealed the presence of ultra-small Si nanocrystals (~4 nm-diam.) in the PLD synthesized samples, while the ICP-SiNWs were found to present both a crystalline cylindrical Si core and/or silicon nano-chains (with a diameter of 4-5 nm) wrapped into an otherwise cylindrical silica layer. Chemical analyses through Energy Dispersive X-ray TEM mapping served to detect the presence of catalyst nanoparticles. Finally, by successfully achieving cathodoluminescence on few nanostructures, we have correlated their light emission energy with their bandgap, which is in turn controlled by their nanosize, as measured by scanning TEM. Moreover, we have been able to discriminate between the light emission truly due to QC effects from that originating from oxygen-based emitting defects in the surrounding silicon oxide shell.

Resume : Many recent studies focus on the formation and the characterisation of silicon nanoclusters (Si-nc) embedded in silica matrix. Such systems have plenty of possible applications: photovoltaic cells, memory devices, waveguide amplifiers… Nevertheless the use of Si-nc in optoelectronic and non-volatile memory devices requires an accurate control of the characteristics of the clusters (size, distribution, composition, nature of the interface between clusters and matrix…) where properties are highly dependent on structural characteristics. In present work, we propose an innovative study on the formation of Si nanoclusters by spinodal decomposition mechanism in silicon rich silicon oxide (SRSO) which appears for high silicon excess. Multilayered SRSO/SiO2 system has been used to control and limit silicon diffusion and thus to fabricate size-controlled nanoparticles. We studied the influence of SRSO layer thickness, SiO2 layer thickness and annealing temperatures using atom probe tomography. These results permit to improve the control of Si nanoclusters growth for silicon excess higher than 30%. Structural results (isolated particles or connected ones) and the influence of parameters (layer thickness or annealing conditions) will be discussed in relation with optical properties.

Resume : Silicon-based nanocrystals represent a promising resource both for next-generation electronic devices and for nano-photonics applications but require precise size, shape and position control. Here we report on the fabrication of mono-crystalline [1] and poly-crystalline [2] Si- and SiGe-based nanocrystals by spontaneous and assisted solid-state dewetting of thin silicon films on insulator (SOI) and on arbitrary silica substrates. Island formation, symmetry, organization and positioning are studied by dark-field optical microscopy and spectroscopy, AFM, TEM and SEM. We demonstrate the capabilities of this top-down/bottom-up hybrid method in engineering the dewetting front thus organizing the nanocrystals in assemblies much more complex than the original etched pattern. The shape of the islands, their number and relative position can be controlled with a precision of ∼ 10%. Our method avoids chemical etching or pattern transfer steps and paves the way for the exploitation of solid-state dewetting for the implementation of complex dielectric oligomers for silicon photonics. Our findings [1,2], open new ways of playing with ordered and disordered metamaterials for thin-film anti-reflection coating and broad band and wide angle light-coupling [3]. Moreover we demonstrate a method for the fabrication of a novel kind of mono-crystalline SiGe-based three dimensional Si-core/SiGe-half shell nanostructure based on solid state dewetting joined with a Ge condensation process [4,5]. This novel class of nanostructures represents a promising device platform for strain-based band-gap engineering and meta-surfaces implementation with dielectric Mie resonators. [1] M. Abbarchi et al., ACS Nano 8, 11181 (2014) [2] M. Naffouti et al., Nanoscale, DOI: 10.1039/C5NR07597A (2016) [3] Spinelli et al., Nat. Comm. 3, 692 (2012) [4] T. David et al., The J. of Phys. Chem. C 119, 24606 (2015) [5] M. Naffouti et al., submitted

Resume : Single-wall carbon nanotubes (SWNTs) are known for their exceptional physical properties ranging from mechanics to electronics and optics. These properties are expected to give rise to innovative applications, especially when nanotubes are incorporated in new functional devices. However, the conception of an effective SWNT-based electronic or optoelectronic technology faces three main concerns: the extraction of semiconducting SWNTs having the desired optoelectronic characteristics from the as-synthetized poly-disperse mixture; the deposition of high nanotube concentrations at desired areas to increases transport and optical performances and the alignment of nanotubes on the substrate. Using an effective polymer-assisted sorting approach, we obtain highly-selective separation of semiconducting SWNTs that can be coupled with optoelectronic silicon-based devices operating at the telecom wavelength of 1.5 µm. Our modified evaporative self-assembly approach can deposit concentrated SWNT networks with configurations varying from random to highly-oriented assembly. In the latter case, the obtained orientation is particularly favorable for device fabrication and operation. Several configurations enabling photo-detection and electroluminescence at the chip level are currently under investigation and the latest results will be presented. This work is funded by the European Union through the FP7 Project CARTOON (Contract FP7 -618025).

Resume : The coupling between light and motion in nano-optomechanical systems enables extremely sensitive displacement measurements as well as nanomechanical actuation through radiation pressure. This provides a powerful way to interface nanomechanical sensor used to detect small force or mass. We explore two approaches to achieving extreme optomechanical coupling strengths, exploiting subwavelength confinement in suitably engineered plasmonic or photonic crystal systems. In a proof-of-principle experiment, we demonstrate how a single dimer nanoantenna attached to a silicon nitride nanomechanical string resonator can be used to read out the Brownian motion of the string, a geometry ideal for highly parallel mass sensing. Moreover, we show that plasmonic forces can be used to actuate a nanomechanical resonator, i.e. a metallic drum suspended tens of nm above a metal surface. In a specially designed silicon photonic crystal nanobeam, we exploit the subwavelength character of a guided optical mode to establish record photon-phonon coupling rates. We use these to perform mechanical displacement measurements with an imprecision at the standard quantum limit, even for a device that has an optical linewidth of ~1 THz. For smaller linewidths, these systems enter a regime of strongly nonlinear optomechanical transduction. We analyze this regime, and demonstrate that in combination with feedback it provides a path to create non-Gaussian states of motion.

Resume : It is well known that Pulsed Laser Deposition (PLD) is a very flexible and versatile technique allowing fast optimization of new and complex material thin films. Among these are Pb(Zr,Ti)O3, PMN-PT, BaTiO3, LiNbO3 and other materials of interest for applications in photonics. Furthermore, the unique features of PLD allow for the integration of “Beyond Moore” materials in CMOS and photonics devices. Using Solmates PLD platform, such devices become now readily available for commercialization. The robust and reliable hardware allows uniform thin film deposition up to 200 mm diameter with high process reproducibility. The process can therefore be easily scaled towards as (pilot) production. In this contribution, wafer scale integration of Solmates high performance PZT thin film is shown on a stress-optic phase modulator in the passive SiN-based TriPleX platform. The PZT piezoelectric thin film is deposited on the wave guide. By applying an electric field across the PZT layer, the phase of propagating light in the structure is controlled. Performance of this new setup will be compared to a conventional approach used in thermo-optic modulation in TriPleX platform. Decrease of power consumption for quasi-DC operation by six orders of magnitude and increase of modulation speed by three orders of magnitude will be demonstrated.

Resume : Silicon photonics has generated strong advances in the last decade for on-chip optical communications. In this context Ge/SiGe quantum wells (QW) have received a growing interest since the first demonstration of the quantum-confined Stark effect (QCSE) in these structures in 2005. This result paved the way to a number of exciting works addressing the absorption mechanisms in Ge/SiGe QW structures. In contrast much less efforts have been made in order to investigate the electro-refractive properties of this material system. Here we report a giant electro-optic effect in Ge/SiGe coupled quantum wells (CQW). This promising effect is based on an anomalous quantum-confined Stark effect due to the separate confinement of both electrons and holes in the Ge/SiGe CQW. This phenomenon can be exploited to strongly enhance optical modulator performance with respect to the standard approaches developed so far in silicon photonics. The CQW structure:(7 nm Ge QW + 1.5 nm Si0.15Ge0.85 inner barrier + 7 nm Ge QW + 26 nm Si0.15Ge0.85 outer barrier) was grown by LEPECVD and then processed into 64 μm long, 100 μm wide planar waveguides by standard UV lithography and ICP-RIE etching. We have measured a refractive index variation up to 2.3×10-3 under a bias voltage of 1.5 V, with an associated modulation efficiency VπLπ of 0.046 Vcm. This demonstration paves the way for the development of efficient and high-speed phase modulators based on the Ge/SiGe material system.

Resume : The exponential increase in data rates in our telecommunication networks drives the need for ever more complex optical transmitters. The core of these optical transmitters is the integrated optical modulator chip. Integrated InP-based modulators are interesting because lasers can be also integrated onto the chip. Due to the small index contrast however, the footprint of InP photonic circuits is larger than photonic circuits based on Si or SiN. Ferroelectric materials such as barium titanate (BTO) or lead zirconate titanate (PZT) offer the highest piezo-electric and electro-optic coefficients available and are ideal candidates for integrated electro-optic modulators on high index contrast photonic platforms. The high quality thin film growth on Si or SiN substrates used in integrated photonics however still remains an important hurdle. In this work we report on the deposition of highly textured PZT thin films on a variety of substrate materials. The key element in the deposition process is an ultra-thin intermediate layer of less than 10 nm. The layer is non-conductive and gives rises to very low propagation losses on PZT clad waveguides. The electro-optic modulation using a co-planar electrode design is recently demonstrated on the SiN platform. With a voltage-length product below 2 V.cm and a propagation loss of less than 1 dB/cm, our deposition method offers interesting possibilities for electro-optic modulation on different material platforms.

Resume : Recently, memristive materials have attracted high interest in the quest for improved electronic and optoelectronic functionalities in silicon technology. Memristive materials memorize the resistance (either in a high or in a low resistance state) after switching off the voltage. Thus, it can be used as an electronic memory (ReRAM) or as an optically readable memory if some optical property (e.g. absorption or light emission) varies between the two states. On the other hand, Si-Al oxynitride (SiAlON) is a material highly compatible with silicon technology that is devised to improve the properties of silicon oxynitrides by adding some Al percentage (1-10%). This allows to reduce the band-gap below silicon nitride (5.5 eV), to improve the conductivity depending on Al concentration, and to help to create memristance through the proper interaction with an Al electrode. In this work, we present an electrical characterization of 100-nm thick SiAlON thin films fabricated by means of pulsed laser deposition on p-type Si substrates. A vertical device structure was achieved by using a shadow mask and depositing either aluminium or indium tin oxide (ITO) on top of the films and full-area Al on the rear side of the substrate. Intensity versus voltage curves have shown a clear switching between two different resistivity states from 10^6 to 10^2 Ohm, showing a good switching repeatability for the two types of contacts. However, the voltage threshold for switching depends on the contact material, being lower in the case of the ITO contact, probably due to its higher ability to interchange oxygen atoms. Finally, the films were also doped with Eu to explore their optoelectronic properties, keeping their memristive switching behaviour.

Resume : In the last decades rare earths (REs) containing materials have been proposed as active media in Si compatible light sources for a wide number of applications, such as lighting for vehicles and flat displays, lab-on-chip sensors for bio-applications, telecommunications. However REs transitions, forbidden by the parity selection rules, become partially permitted only in presence of a crystalline field. Otherwise heavy metals with ns2 electronic configuration as bismuth can be stabilized in many oxidation states, exploiting permitted transitions characterized by a much more intense emission. The introduction of Bi in Si-based materials suffers from some limits, such as the Bi precipitation after high temperature treatments and Bi-Bi deleterious interactions as concentration quenching. In order to solve these limits in Si-based materials, we have synthetized Bi and Bi-Er co-doped yttrium compounds by ion implantation and magnetron co-sputtering. The Bi influence on structural and optical properties has been studied and will be widely discussed. In particular the possible tuning of the emission from the blue to the orange by controlling the Bi oxidation state or the excitation wavelengths will be evidenced, making it a suitable element to realize white sources. In addition a highly efficient emission from Er ions at 1.54 um has been obtained through an energy transfer from Bi ions, thus suggesting these compounds as efficient materials for photonic applications.

Resume : The rare earth doping of Si has attracted a lot of interest as a means to obtain efficient light emission at 1.5µm. However, the main reasons behind the insufficient luminescence efficiency of the Er doping process have scarcely been investigated. In this work, Er-doped Porous Silicon (PSi) layers have been characterized by room temperature photoluminescence (PL), energy dispersive spectroscopy by scanning electron microscopy (SEM-EDS), X-ray absorption spectroscopy (XAS) at the Er-LIII edge, 3D electron tomography (ET). The thermal annealing has been performed under Ar or N2 using different annealing temperatures and times. The PSi fabrication parameters have been related to Er local environment, Er distribution within the pores and PL. Differences in PL and Er-O coordination following different thermal treatments are evidenced. The study indicates an advantage of the N2 treatment, whose reducing behavior is stronger than that of Ar and then facilitates the lowering the Er-O bond length and the increasing of the room temperature PL intensity. The authors acknowledge access to the nanocharacterization platform (PFNC) at the Minatec Campus in Grenoble and ESRF for beamtime. REFERENCES [1] G. Mula et al., J. Phys. Chem. C 116, 11256 (2012) [2] G. Mula et al., Nanoscale Res. Lett. 9, 332 (2014) [3] T. Printemps et al., Ultramicroscopy 160, 23 (2016) [4] P. Noé et al. J. Appl. Phys. 102, 103516 (2007).

Resume : This work reports the observation of visible white electroluminescence (EL) at RT from forward-biased Al/p+-Si/PS-ZnO/ITO (Aluminum/p+-Si/porous Silicon-Zinc Oxide/Indium Tin Oxide) structures. Light is produced in the PS-ZnO layer combining the red-orange emission obtained from exciton recombinations in PS due to quantum confinement in Si quantum dots (QDs) and the blue-green emission from deep-level intrinsic defects present in ZnO. PS-ZnO composites are synthesized using electrochemically etched PS substrates as host material for the ZnO sol-gel nucleation. This technique has been chosen because it is versatile, cheap and allows the proper infiltration of ZnO precursors into the porous matrix enhancing the interaction between both materials. PS-ZnO composites are annealed in the presence of oxygen to produce a passivating oxide at the PS surface and to crystallize and induce a proper density of intrinsic defects in ZnO crystals that improve the n-type character as well as contribute to the broadband emission across the whole visible range. The proposed device is completed by forming a conductive transparent ITO contact on the surface. Current-voltage (J-V) characteristics have been studied at RT, showing that the main transport phenomena is direct tunneling (DT) at low bias voltages and Fowler-Nordheim (FN) tunneling at high polarization voltages for both forward and reverse bias conditions. Visible EL is only achieved when the conduction mechanism at forward bias voltages changes from DT to FN, at VFB>3.9±0.2 V. Its spectra is composed by three main bands in the visible range centered at ~490 (light blue), ~550 (green) and ~620 nm (orange) producing together white light. An energy band diagram is proposed to explain the different conduction mechanisms. These results suggest that PS-ZnO composites may be of interest for the development of solid-state Si-based white-light electroluminescent devices compatible with current integrated circuit (IC) technology.

Resume : Recently, rare earth (RE)-doped thin films have attracted the attention of the research community due to their well-defined emission energies. The proper election of the RE species allows tuning light emission in a range spanning from visible to the infrared. As well, the use of the adequate semiconductor and/or dielectric matrix is crucial for the optical activation of the RE ions. ZnO is a good candidate with a large band-gap energy semiconductor compatible with Si technology, allowing for efficient electron injection and energy transfer to the RE. In this work, the optical, electrical and electroluminescence (EL) properties of Tb- and Eu-codoped ZnO thin films are reported from different doped devices The films were deposited on p-type Si substrate by sputtering the RE together with ZnO, and afterwards annealed at 700 °C. Photoluminescence revealed that the RE ions are optically active within the ZnO matrix. An electrical study on (n)ITO / Eu,Tb:ZnO / p-Si / Al devices indicated variable range hopping as the main transport mechanism governing the Eu,Tb:ZnO system. The EL emission was found to be particularly intense (visible to the naked eye) after electrical excitation in inversion regime. It was attributed to both defects within the ZnO lattice and allowed electronic transitions within Eu ions. The latter contribution is a consequence of a combination of direct impact excitation of Eu ions and energy transfer from both the ZnO matrix and excited Tb ions to Eu.

Resume : In recent years, rare earths (REs) doped inorganic materials have been widely applied in lighting, display devices and photonics. Among the different REs, a particular interest has been devoted to Eu, which is stable both in its 2 and 3 states. In particular, emission of Eu2 is quite strong and consists of a broad peak in the 400-600 nm range. Eu3 emission, instead, presents several sharp peaks at around 600 nm whose intensity is low. In this work Eu-doped SiOC thin films have been synthesized by RF magnetron co-sputtering. Optical properties of the these films have been investigated by photoluminescence (PL) and cathodoluminescence (CL) measurements. In both cases a very bright Eu2 light emission in the 400-600 nm range has been obtained by properly changing the Eu concentration in the films. In addition, bilayers consisting of two SiOC films doped with different Eu concentrations have been synthesized. A proper choice of the annealing temperature allows us to obtain an intense PL white emission. Furthermore, CL measurements have demonstrated that by properly varying the electron beam energy it is possible to control at the nanoscale the electron penetration depth inside the bilayer, thus obtaining a depth-resolved CL, with a continuous tuning of the emission from 400 to 600 nm. The very efficient PL and CL signals and the compatibility with Si technology open the way to new and promising applications of Eu-doped SiOC in lighting, display technology and photonics.

Resume : Silicon based materials hold up to this day the most important research in optoelectronics, nowadays the so called oxi-, nitrides- and oxynitrides provide the most required advantages for integrated devices. Furthermore, the aggregation or doping of particular elements such as rare earth ions, yield specific emissions for each desired purpose. SiAlON compounds are specially suitable because depending of the specific content of oxygen and nitrogen their optical and electrical response can be suitably tuned. In the present work, we will show the optical properties and performance of thin films prepared by pulsed laser deposition from independent ablation of a commercially available ceramic SiAlON target and a pure europium (Eu target). The films were prepared forming a multilayer nanostructure formed by SiAlON Eu-doped layers. Depending on the specific structure both oxidation states of Eu (Eu2 and Eu3 ) can be obtained. As a result the emission of the film by photoluminescence (PL) under laser excitation, cathodoluminescence (CL) under electron excitation and finally the electroluminescence (EL) under current excitation show the characteristic emission of each ion. As a result wide band across the visible range or discrete emission peaks can be achieved. The different mechanisms of excitation of the Eu ions will be discussed.

Resume : The presence of an indirect band gap in bulk silicon (Si) makes it a poor light emitter and has prevented its application as a light source for integrated photonics. Rare earth (RE) ions incorporated silicon nanoparticles in silica thin films have emerged as promising route to obtain light from Si-based materials. However, the light emission in such system is strongly dependent on the nanostructure. We perform a systematic investigation on the effect of annealing temperature and RE content on the spatial distributions of Si and RE atoms, their spatial relationships and their precipitation kinetics by means of Atom Probe Tomography (APT). We observe similar nanostructural evolution for two different RE elements; cerium (Ce) and erbium (Er). Annealing at 900°C leads to the formation of a non-stable mixed Si-O-RE phase. When annealing temperature rise to 1100°C, we notice a phase separation between pure Si nanoparticles and RE-silicate phase (RE2Si2O7). Moreover, we observe a preferential segregation of Si atoms on the RE-silicate surface forming thereby snowman-like particles. Finally, the optical properties of the analyzed samples have been investigated by means of photoluminescence (PL) and correlated to the nanostructure obtained by APT. For the Ce-doped samples, the formation of Ce2Si2O7 phase reveals a high Ce-related PL intensity. In contrast, this was not the case for Er-doped samples where Er ions are excited indirectly via the Si-nanoparticles. Furthermore, we show that Si-nanoparticles PL strongly depends on RE content in the samples.

Resume : Among all rare earths, Cerium has an allowed 5d-4f transitions which results in an intense blue emission. This 5d band is a continuum of energy levels offering a wide absorption- emission band which is affected by the matrix. Those remarkable properties make Ce ions good light emitters which could be integrated in LED devices. The aim of this study is to elaborate luminescent Ce3+ doped SiOxNy films. Those layers are deposited by using radio frequency sputtering technique with N reactive flow and the Ce emission is optimized through the deposition and annealing parameters. By adjusting the deposition parameters, different oxynitride compositions have been produced with different optical indices. Such an index variation affects the structural environment and more precisely the emission peak position. Excitation photoluminescence measurements show a wide excitation domain for the Ce3+ ions ranging from 300 nm up to 400 nm wavelength and photoluminescence measurements reveal a wide and bright luminescence centered at 480 nm under a 325 nm wavelength excitation. This blue emission could be adapted for LED applications. This study paves the way of a potential use of Ce doped SiOxNY films for electroluminescent devices provided that a higher doping rate is reached due to the inclusion of nitrogen.

Resume : The efficiency of solar cells is limited by either thermalization processes induced by the absorption of photons with energy larger than the bandgap or by non-absorbed photons with energy smaller than the bandgap. Adapting the solar spectrum to the cell by photon conversion processes has emerged as a possible route to reduce these limitations and to enhance the solar cell efficiencies. Therefore, down conversion layers that enable to convert ultraviolet (UV) photons into near infrared (NIR) photons are required. In this work, we investigate SiOx thin films co-doped with both Cerium (Ce) and Ytterbium (Yb). Unlike other rare earth elements, Ce3+ ions are characterized by an electric dipolar allowed 5d-4f transition leading to a strong absorption in the violet-blue. Moreover, Yb is of particular interest for Si-based solar cells since its emission is observed at around 980 nm, slightly above the Si bandgap. The growth of SiOx films and the (Ce, Yb) co-doping were performed by e-beam evaporation and effusion cells, respectively. The structural and optical properties were studied by IR absorption, Raman and photoluminescence (PL) spectroscopies. The influence of rare earth concentration and annealing temperature is discussed. We provide evidence of the indirect excitation of Yb ions. Both PL excitation and PL decay time measurements demonstrate the existence of an energy transfer from Ce to Yb. Quantum yield measurements will be discussed in relation with potential applications.