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Hybrid Concentrated Photovoltaics (HCPVs) are systems in which additional low-cost silicone solar cells are added to take advantage of the power generated by the diffuse radiation lost when using only multi-junction cells that work only with direct radiation. The work has been tested by simulating the performance of a hybrid CPV system composed of a Fresnel lens associated with a pyramid, multi junction cell as well as additional silicon solar cells. This proposal is compared with an ordinary CPV system and a system based on only silicon solar cells. The simulation results show that the CPV makes it possible to have a high optical efficiency of 94% at the pyramid exit for direct radiation, but this high efficiency rapidly decreases to 0% for diffuse radiation. In this case, the silicon solar cell comes into the scene to converts these diffused or non-concentrated rays into electricity, with an optical efficiency of 85%. It was also found that the Hybrid CPV system was able to increase the power by 21% compared to the CPV system.

International audience; We demonstrate the fabrication of vertical InGaN light-emitting diodes (LEDs) on large-area free-standing membranes, using a mechanical lift-off technique enabled by 2D h-BN. 30 μm-thick electroplated copper deposited on the epilayer (i) gives rigidity to the structure, preventing crack generation, (ii) functions as a back mirror and as a heat sink, and (iii) enables one-step self-lift-off and transfer of LED structures from h-BN/sapphire during a thermal treatment at 100 °C. Free-standing arrays of LEDs on thick membranes were processed and their electro-optical performance was characterized. This approach can provide a solution for the fabrication of low-cost, wafer scale, crack-free, and highly reproducible free-standing arrays of vertical LEDs with up to centimeter-size areas.

International audience; We present a critical study of LEDs on h-BN compared to the conventional LEDs on sapphire from materials characterizations, device fabrication to the device performances measurements performed before and after liftoff and transfer with and without intermediary adhesion layer to arbitrary substrates.

International audience; Combined photonic and electronic systems require diverse devices to be co-integrated on a common platform. This heterogeneous integration is made possible through several separation and transfer methods where the functioning epilayers are essentially released from their growth substrate. The use of 2D layered h-BN as a mechanical release layer has been demonstrated to be a promising technique for the hybrid integration of III-nitride devices. In this talk we will give an overview of our results on wafer-scale van der Waals epitaxy by MOVPE of different III-N heterostructure devices such as LEDs, HEMTs, solar cells, sensors and photodetectors. Furthermore, mechanical release and transfer techniques of crack-free III-N devices on foreign substrates will be presented along with a comparison between the device performances before and after transfer.

Reliable p-doped hexagonal boron nitride (h-BN) could enable wide bandgap optoelectronic devices such as deep ultra-violet light emitting diodes (UV LEDs), solar blind photodiodes and neutron detectors. We report the study of Mg in h-BN layers as well as Mg h-BN/AlGaN heterostructures. Mg incorporation in h-BN was studied under different biscyclopentadienyl-magnesium (Cp2Mg) molar flow rates. 2&theta, &omega, x-ray diffraction scans clearly evidence a single peak, corresponding to the (002) reflection plane of h-BN with a full-width half maximum increasing with Mg incorporation in h-BN. For a large range of Cp2Mg molar flow rates, the surface of Mg doped h-BN layers exhibited characteristic pleats, confirming that Mg doped h-BN remains layered. Secondary ion mass spectrometry analysis showed Mg incorporation, up to 4 &times, 1018 /cm3 in h-BN. Electrical conductivity of Mg h-BN increased with increased Mg-doping. Heterostructures of Mg h-BN grown on n-type Al rich AlGaN (58% Al content) were made with the intent of forming a p-n heterojunction. The I-V characteristics revealed rectifying behavior for temperatures from 123 to 423 K. Under ultraviolet illumination, photocurrent was generated, as is typical for p-n diodes. C-V measurements evidence a built-in potential of 3.89 V. These encouraging results can indicate p-type behavior, opening a pathway for a new class of wide bandgap p-type layers.

Selective Area van der Waals Epitaxy (SAVWE) of III-Nitride device has been proposed recently by our group as an enabling solution for h-BN-based device transfer. By using a patterned dielectric mask with openings slightly larger than device sizes, pick-and-place of discrete LEDs onto flexible substrates was achieved. A more detailed study is needed to understand the effect of this selective area growth on material quality, device performance and device transfer. Here we present a study performed on two types of LEDs (those grown on h-BN on patterned and unpatterned sapphire) from the epitaxial growth to device performance and thermal dissipation measurements before and after transfer. Millimeter-size LEDs were transferred to aluminum tape and to silicon substrates by van der Waals liquid capillary bonding. It is shown that patterned samples lead to a better material quality as well as improved electrical and optical device performances. In addition, patterned structures allowed for a much better transfer yield to silicon substrates than unpatterned structures. We demonstrate that SAVWE, combined with either transfer processes to soft or rigid substrates, offers an efficient, robust and low-cost heterogenous integration capability of large-size devices to silicon for photonic and electronic applications.

The epitaxy of III-V semiconductors on silicon substrates remains challenging because of lattice parameter and material polarity differences. In this work, we report on the Metal Organic Chemical Vapor Deposition (MOCVD) and characterization of InAs/GaAs Quantum Dots (QDs) epitaxially grown on quasi-nominal 300 mm Ge/Si(001) and GaAs(001) substrates. QD properties were studied by Atomic Force Microscopy (AFM) and Photoluminescence (PL) spectroscopy. A wafer level &micro, PL mapping of the entire 300 mm Ge/Si substrate shows the homogeneity of the three-stacked InAs QDs emitting at 1.30 &plusmn, 0.04 &micro, m at room temperature. The correlation between PL spectroscopy and numerical modeling revealed, in accordance with transmission electron microscopy images, that buried QDs had a truncated pyramidal shape with base sides and heights around 29 and 4 nm, respectively. InAs QDs on Ge/Si substrate had the same shape as QDs on GaAs substrates, with a slightly increased size and reduced luminescence intensity. Our results suggest that 1.3 &mu, m emitting InAs QDs quantum dots can be successfully grown on CMOS compatible Ge/Si substrates.

AlGaN/GaN HEMTs have been shown to be efficient sensors for a broad range of physical parameters, in either liquid or dry condition, such as pressure sensor [1,2], gas detection [3,4], pH sensor [5], and more recently used as biosensors for the rapid detection of viruses [6]. These achievements could pave the way for the use of these HEMT transistors in electronic nose development particularly useful for volatile organic compound (VOC) detection. Among VOCs, acetone is one of the most important elements because it can be used as a biomarker for early disease, such as lung cancer, detection. For this purpose, sensors with responsivity in the range below 1 ppm are desired [7]. Up to now, only few works have been reported on acetone detection with rather contradictory observations between its detection at room temperature (RT) [8] or high temperature [9]. In this work, we report on AlGaN/GaN HEMT sensors for acetone concentration below 100 ppm and in a broad range of the sensor temperature varying from (RT) to 300°C. At RT, in presence of acetone, a smooth and monotonic decrease of the current is observed with a rather large responsivity of 15µA/ppm and with large response time (several minutes) and memory effect. This decrease of the current can be explained by the electrostatic interaction between the 2D gas in the HEMT with the dipolar moment of the acetone molecules as described by Neuberger et al. [8]. This decrease is also in agreement with the work of Neuberger. et al [8]. At high temperature (300°C), in contrary to what has been reported in [9], a current decrease is first observed just after the acetone injection and then followed by an increase which saturates and stabilizes at a constant value. In order to clarify this unexpected behavior, a detailed study of the sensors response versus the temperature and acetone injection mode has been carried out. The output of this investigation is that a competition between the current variations induced by both the sensor and gas flow temperature difference from one side and acetone dipolar moment from the other side can explain this transient. At high temperature, the gas flow (especially for high acetone concentration) tends to cool down the sensor inducing an increase of the current, whereas the true acetone effect leads to a decrease of the current. AlGaN/GaN HEMTs – based sensors are shown to allow for very sensitive acetone detection at both room and high temperature. Nevertheless, care must be taken during the characterization and operation of such sensors especially at high operating temperature. Increasing the latter, can help to improve the sensor response suppress the memory effect, but requires the control or the cancellation of the current transient due to the temperature difference between the gas flow and the transistor gate. References [1] Kang, B.S.; Kim, S.; Kim, J.; Mehandru, R.; Ren, F.; Baik, K.; Pearton, S.J.; Gila, B.P.; Abernathy, C.R.; Pan, C.C.; Chen, G.T.; Chyi, J.I.; Chandrasekaran, V.; Sheplak, M.; Nishida, T.; Chu, S.N.G., AlGaN/GaN high electron mobility transistor structures for pressure and pH sensing. physica status solidi (c) 2005, 2, 2684–2687. doi:10.1002/pssc.200461269. [2]. Gajula, D.; Jahangir, I.; Koley, G., High Temperature AlGaN/GaN Membrane Based Pressure Sensors, Micromachines 2018, 9, 207. doi:10.3390/mi9050207. [3] Bishop, C.; Halfaya, Y.; Soltani, A.; Sundaram, S.; Li, X.; Streque, J.; Gmili, Y.E.; Voss, P.L.; Salvestrini, J.P.; Ougazzaden, A., Experimental Study and Device Design of NO, NO2, and NH3 Gas Detection for a Wide Dynamic and Large Temperature Range Using Pt/AlGaN/GaN HEMT, IEEE Sensors Journal 2016, 16, 6828–6838. doi:10.1109/jsen.2016.2593050. [4] Halfaya, Y.; Bishop, C.; Soltani, A.; Sundaram, S.; Aubry, V.; Voss, P.; Salvestrini, J.P.; Ougazzaden, A. Investigation of the Performance of HEMT-Based NO, NO2 and NH3 Exhaust Gas Sensors for Automotive Antipollution Systems. Sensors 2016, 16, 273. doi:10.3390/s16030273. [5] Sama, N.Y.; Bouhnane, H.; Gautier, S.; Ahaitouf, A.; Matray, J.M.; Salvestrini, J.P.; Ougazzaden, A.; Hathcock, A.; He, D.; Vuong, T.Q.P.; Karrakchou, S.; Ayari, T.; Mballo, A.; Bishop, C.; Halfaya, Y., Investigation of Sc2O3 Based All-Solid-State EIS Structure for AlGaN/GaN HEMT pH Sensor, 2019 IEEE SENSORS. IEEE, 2019. doi:10.1109/sensors43011.2019.8956762. [6] Yang, J.; Carey, P.; Ren, F.; Mastro, M.A.; Beers, K.; Pearton, S.J.; Kravchenko, I.I., Zika virus detection using antibody-immobilized disposable cover glass and AlGaN/GaN high electron mobility transistors, Applied Physics Letters 2018, 113, 032101. doi:10.1063/1.5029902. [7] Wilson, A., Advances in Electronic-Nose Technologies for the Detection of Volatile Biomarker Metabolites in the Human Breath, Metabolites 2015, 5, 140–163. doi:10.3390/metabo5010140. [8] Neuberger, R.; Muller, G.; Ambacher, O.; Stutzmann, M., High-Electron-Mobility AlGaN/GaN Transistors (HEMTs) for Fluid Monitoring Applications, physica status solidi (a) 2001, 185, 85–89. doi:10.1002/1521-396x(200105)185:1 3.0.co;2-u. [9] Sun, J.; Sokolovskij, R.; Iervolino, E.; Santagata, F.; Liu, Z.; Sarro, P.M.; Zhang, G., Characterization of an Acetone Detector Based on a Suspended WO3-Gate AlGaN/GaN HEMT Integrated With Microheater, IEEE Transactions on Electron Devices 2019, 66, 4373–4379. doi:10.1109/ted.2019.2936912. [10] Rabbaa, S.; Stiens, J. Validation of a triangular quantum well model for GaN-based HEMTs used in pH and dipole moment sensing. Journal of Physics D: Applied Physics 2012, 45, 475101. doi:10.1088/0022-3727/45/47/475101.

In this paper, we propose a comparative study of two Micro photovoltaic concentrator systems (MCPV); the first is based on a Fresnel lens associated with a dome lens as secondary optical element. The second one is composed of two lenses the first is a Plano-convex lens, while the secondary is a dome lens. We studied and analyzed several parameters including large range of wavelengths. The two systems are compared in terms of optical efficiency and acceptance angle. In addition, the distribution of irradiance on the solar cell is also studied. Results show that the system composed of Polymethyl methacrylate (PMMA) Plano convex lens associated with a dome presents the highest optical efficiency regarding the non uniformity of flux, however, the two systems allow a large acceptance angle if they are made of Polycarbonate (PC).

International audience; In this work, an all-solid-state electrolyte-insulator-semiconductor (EIS) device is developed for pH sensing performance evaluation of insulating materials. The EIS capacitor incorporates scandium oxide (Sc2O3) sensing film deposited on undoped gallium nitride (u-GaN) by thermal evaporation. The structural and morphological features of the thin films annealed at different temperatures (650-850°C), were investigated through X-ray diffraction and AFM analysis. A gold wire with diameter of 25 µm was bonded on the device and served as the quasi reference electrode for the C-V measurements and pH sensitivity characterizations. After correction of the measured capacitance regarding the pH dependent variation of the standard potential E0(pH) of gold, the Sc2O3 EIS capacitor prepared with an annealing at 650°C exhibited a linear response with a sensitivity of 40 mV/pH while the device with the as-deposited Sc2O3 film showed nonlinear behavior and, those annealed at temperature higher than 650°C were shown to be insensitive to pH variation.

International audience; InGaN nano-structures, grown using nano selective area growth, have been shown to exhibit high crystalline quality, even for high In content InGaN alloy, and reduced polarization charge effect. They are thus very attractive for the realization of high efficiency solar cells. Compared to planar InGaN absorbers, nanopyramid-based absorbers are shown to relax the usual challenging constraint on the doping of the p-GaN layer, which would be needed to overcome the polarization-induced electric field. NP-based solar cells maintain the same performance with ten times lower p-GaN doping. Furthermore, the SiO2 mask used for selective area growth of the nanopyramids is shown to help trap light into the nanopyramids, leading to increased optical absorption and thus efficiency. Last, InGaN nanopyramid absorber-based solar cells can allow for a higher InGaN residual donor concentration than that of the planar InGaN solar cells. Overall, an optimized In0.3Ga0.7N nanopyramid-based solar cell can lead to an efficiency twice than that of a planar InGaN-based solar cells with standard p- and n-GaN doping level. As a proof of concept, an In0.09Ga0.91N nanopyramid-based solar cell has been fabricated and is shown to have larger short circuit photocurrent and open circuit voltage than a state of the art In0.08Ga0.92N-based planar solar cell.

Lab-on-chip (LOC) is recognised as one of the most affordable solutions for integrating electronics and fluidics devices. In this field, bonding plays a vital role because it provides the means for attaching multiple components onto a substrate, transforming them into a microfluidic circuit. Bonding is an integral step, especially when designing a device that is free from leakage and eventual clogging. A comprehensive review of the latest irreversible bonding technologies is discussed in this paper, in which the focus is on the layered microfluidic systems with large sensor arrays. This review covers microfluidic devices fabricated from a rigid-type glass–fibre-printed circuit board and a thermoplastic flexible printed circuit with 186 references whose development date back three decades ago. The bonding techniques are organised into the following four groups: (a) adhesive bonding, (b) thermal and solvent bonding, (c) surface modification and dry bonding and (d) photoresist groups. Other techniques are available beyond these groupings, but they can be classified into the nearest group to facilitate the discussion. This paper will benefit researchers and practitioners aiming to develop polymer-based LOC devices.

International audience; It is shown that deep level transient spectroscopy can be carried out on Schottky diodes to investigate, in addition to majority carrier traps, minority carrier traps. This is possible thanks to the application of a large reverse bias to the device which allows minority carrier injection by lowering their corresponding effective Schottky barrier height. Indeed, when increasing the reverse bias voltage, the deep level transient spectroscopy signal, initially negative and thus showing only majority carrier traps signature, becomes positive, revealing minority carrier traps involvement. A careful analysis of the recorded spectra leads to the identification of four minority carrier traps which have been so far only evidenced using dedicated technique such as minority carrier transient spectroscopy.

Two stages optical concentrators for concentrated photovoltaic (CPV) are studied both experimentally and theoretically. They are composed of a Fresnel lens made of PMMA and coupled to two different secondary optical elements (SOEs) types: a pyramid and a cone made of fused silica. Results, in terms of optical efficiency and acceptance angle, show that the pyramid-type is the best choice for the secondary optical element.Two stages optical concentrators for concentrated photovoltaic (CPV) are studied both experimentally and theoretically. They are composed of a Fresnel lens made of PMMA and coupled to two different secondary optical elements (SOEs) types: a pyramid and a cone made of fused silica. Results, in terms of optical efficiency and acceptance angle, show that the pyramid-type is the best choice for the secondary optical element.

The study concerns the use of four secondary optical elements (SOE) in a photovoltaic solar concentrator using the same primary optic element: the Fresnel lens. In this work, a detailed optical modeling is applied to analyze the performance of four refractive secondary optical elements: the Compound Parabolic Concentrator (CPC), the Crossed Compound Parabolic Concentrator (Crossed CPC), the Cone and the Pyramid. Two of the most used materials for manufacturing secondaries are employed, to get a clear idea about the four elements efficiencies and geometrical needs. Efficiencies are compared in term of achieved concentrations, acceptance angle, and the output light power distribution. The geometrical considerations reveal that the length and the input aperture size of the four SOEs increase if the refractive index of the considered material increases. Results show that the pyramid gives the more uniform irradiance distribution and the high optical efficiency whatever the used material, and a largest tolerance angle compared to other authors

We report a comparison of the morphological, structural and optical properties of both InGaN single-layer and multilayered structures, the latter consisting of periodic thin GaN interlayers inserted during InGaN growth. It is shown that such a structure suppresses the In concentration fluctuations and corresponding different states of strain relaxation with depth, both detrimental to solar cell applications. Measurements performed by X-ray diffraction, cathodoluminescence and photoluminescence demonstrate that this multilayer growth is a promising approach to increase both the InGaN layer total thickness and In content in InGaN epilayers. As an example, single-phase 120 nm thick InGaN with 14.3% In content is obtained and found to possess high structural quality.

International audience; The aim of the presented work is to determine the optimum height and front surface arc angle of dielectric totally and internally reflecting concentrator associated with a Fresnel lens for solar concentrators used in photovoltaic systems. Ray tracing technique was used to simulate the optical characteristics of this CPV unit with various design parameters. An optimum concentrator was determined by varying sizes of the secondary optic and using two materials: the Fused Silica and the BK7.

This study presents performances comparison of optical and geometrical properties of two optical concentrators: A Compound Parabolic Concentrator (CPC) and a Dielectric Totally Internally Reflecting Concentrator (DTIRC). These concentrators are used as a secondary optical element in both cases with and without a Fresnel lens as a primary stage. Results show that the optical efficiency is almost equal for the two concentrators if used alone, and obviously decreases when a primary stage is added. Regarding the size of the elements we found that the length, the input radius and the concentration ratio of DTRIC increase with the increment of the acceptance angle, however, the length, the input radius and the concentration ratio of CPC decrease. Also we notice that the two lengths are equal in the angle 48°, and the input radius and the concentration ratio are equal in the acceptance angle 30°.

This study presents a comparison of two optical concentrators: A crossed Compound Parabolic Concentrator (CCPC) and a pyramidused as a secondary optical element with and without the primary stage, a Fresnel lens. Results show that the optical efficiency is higher in the case of the pyramid if used alone, andevidently decreases when a primary stage is added. Compared to CCPC, the pyramid as secondary optical element is more efficient. Regarding the size of the elements, it is found thatthe length and the inlet radius of each optical element decrease when the acceptance angle increases. The CPC presents the larger inlet radius and the longer length for as long as the acceptance angle is less than 45°, beyond this value, the two lengths are equal.

Thin films of boron nitride (BN) have been deposited at low temperature (below 300 °C) by microwave plasma-enhanced chemical vapor deposition (PECVD), using borane dimethyl amine, as boron precursor. The plasma was composed of a mixture of argon and nitrogen and was excited with a microwave power. In addition, a radiofrequency signal was applied to the substrate holder in order to negatively bias the sample during the deposition process. The characterization has been performed by infrared transmittance spectroscopy, and the influence of the bias on the deposition of the films has been studied. We have observed that the behaviour of the layers is that of an anisotropic uniaxial medium, and that they are composed of a collection of nanocrystallites of the hexagonal phase. These crystallites are textured with the very same orientation of their c-axis relative to the normal of the sample. By performing the IR transmittance measurements at oblique incidence, additional bands of absorption related to longitudinal optical vibration modes allow us to determine very easily this texturation. The applied bias is shown to have a direct influence on it, the larger the voltage, the more the crystallites are oriented parallel to the sample surface, until a sputtering regime is reached at an even higher voltage.

International audience; We present a generalized study of light emission from reverse biased p–n junctions under avalanche breakdown conditions. A model is developed based on direct and indirect interband processes including self-absorption to describe measured electroluminescence spectra. This model was used to analyze experimental data for silicon ~Si! and gallium arsenide p–n junctions and can be extended to several types of semiconductors regardless of their band gaps. This model can be used as a noninvasive technique for the determination of the junction depth. It has also been used to explain the observed changes of the Si p–n junction electroluminescence spectra after fast neutron irradiation. In particular, it is demonstrated that the neutron irradiation affects both the semiconductor and the overlying passivation oxide layer.

This work is focused on the conducted transport mechanisms involved on devices based in gallium nitride GaN and its alloys. With considering all conduction mechanisms of current, its possible to understanded these transport phenomena. Thanks to this methodology the current-voltage characteristics of structures with unusual behaviour are further understood and explain. Actually, the barrier height (SBH) is a complex problem since it depends on several parameters like the quality of the metal-semiconductor interface. This study is particularly interesting as solar cells are made on this material and their qualification is closely linked to their transport properties.

The temperature effect on electroluminescence spectra of silicon p–n junctions under avalanche breakdown condition is investigated. Two different cases are considered in the framework of the indirect interband recombination model including the self absorption effect. The first is when the electric field remains constant when the temperature varies, and the second is when, for each temperature, the electric field is modified following the variation of the avalanche breakdown voltage versus temperature. It is shown that, with a constant electric field, the electroluminescence intensity increases as observed in experimental measurements, whereas a small and negligible increase of the electroluminescence intensity is obtained with a modified field.

Bias dependence of the integrated room temperature photoluminescence (PL) intensity and capacitance measurements, are used to study the interface properties of metal–insulator–semiconductor (MIS) structures realized on indium phosphide (InP). Boron nitride (BN) insulating films have been grown by a radio-frequency (RF) plasma enhanced chemical vapor deposition (PECVD) technique. The capacitance–voltage ( C – V g ) measurements are performed in the dark and under illumination. The Terman's method was first used to analyze the interface sates distribution. The results proved to be non-reliable. Indeed low (≤5×10 11 cm −2 eV −1 ) and even negative values were obtained particularly from the dark capacitance data. The interface states density is also determined from PL intensity variations versus applied voltage. The obtained distributions of interface states are U shaped with a minimum, nearly 10 12 cm −2 eV −1 , located around 0.4 eV below the conduction band minimum. This technique, which is frequency independent and less sensitive to the leakage currents in the insulator, leads to more reliable results.

Current voltage ( I–V g ) and deep level transient spectroscopy (DLTS) techniques have been carried out to study Schottky and ultraviolet oxidised Schottky diodes realised on n-type indium phosphide. For the oxidised structures, the ideality factor n versus voltage exhibits a peak around 0.2 V, from which the interface state density can be estimated to have a maximum value of 4×10 12 cm −2 eV −1 . Comparable results for the same structures have been obtained from DLTS measurements. For the Schottky diodes, no peak appears in the plot of n versus voltage and no information on interface states can be deduced from I–V g measurements. However, DLTS measurements reveal an electrically active defect localised at the InP interface. This study shows that the I–V g measurements may be used as a fast technique for interface states investigation.

Current–voltage ( I – V g ), capacitance–voltage ( C – V g ) and photoluminescence intensity variations versus bias voltage ( I p – V g ) are carried out to study Schottky and UV oxidized Schottky diodes realized on n-type indium phosphide. It is shown that the electrical properties of the two types of structures are comparable and are governed by a thin interfacial layer even in the case of the non-oxidized structures. The photoluminescence measurements however led to a net distinction between the two types of structures. The results show that even in the initially oxidized structures, the thickness of the interfacial oxide is greater than expected probably due to further oxidation during the long storage in air. The photoluminescence results show that these samples exhibit a MIS, rather than a Schottky behaviour. Finally, the interface states density has been estimated from the photoluminescence intensity variations versus applied voltage.

Electrical properties of n-InP metal–semiconductor diodes with S-treated, annealed S-treated and as-etched (non-treated) surfaces are investigated. The Schottky barrier heights (SBH) are estimated from current–voltage ( I – V ) and capacitance–voltage ( C – V ) measurements made between 220 and 320 K. For S-passivated contacts, it is shown that the SBH remains nearly constant, around 0.6 eV, in the investigated temperature range, whereas for the untreated surfaces, the SBH increases linearly with temperature. The ideality factor, n , is temperature-dependent for the as-etched samples and nearly constant, ≈1.1, for the S-treated contacts. This behavior is discussed in terms of the interfacial layer model. For the non-treated samples, the n versus V curve exhibits a peak around 0.3 V, from which the interface states density can be estimated, with a maximum value of 4×10 12 cm −2 eV −1 . Such voltage dependence of n has not been observed initially for the S-passivated structures and appears only after prolonged air exposure, with a less pronounced evolution for the annealed samples, showing the beneficial effect on the stability and the contact quality of these structures.

International audience; This paper focuses on a comparative study of optical, morphological, microstructural and microcompositional properties of typical InGaN samples which exhibit V-defects but also two additional surface defects features, referred to as inclusion#1 (Ic1) and inclusion#2 (Ic2). HR-XRD, AFM, SEM, STEM and EDX are used to characterize such defects. Furthermore, hyperspectral mapping, spot mode and depth-resolved CL measurements provided useful informations on the optical emission properties and microstructure. The main characteristic of Ic1 luminescence peak is a decrease in intensity and no obvious shift in the CL peak position when going from the outside to the middle of such defect. More interesting was Ic2 which is shown to be local 3D top surface In-rich InGaN domains embedded in an homogeneous InGaN matrix. In fact, this study pointed out that close to the interface GaN/InGaN, it exists a 30 nm thick fully strained InGaN layer with constant indium incorporation. As the growth proceeds spatial fluctuation of the In content is observed and local In-rich 3D domains are shown to emerge systematically around threading dislocations terminations.

GaN was grown on ZnO-buffered c-sapphire (c-Al2O3) substrates by Metal Organic Vapor Phase Epitaxy. The ZnO then served as a sacrificial release layer, allowing chemical lift-off of the GaN from the c-Al2O3 substrate via selective wet etching of the ZnO. The GaN was subsequently direct-wafer-bonded onto a glass substrate. X-Ray Diffraction, Scanning Electron Microscopy, Energy Dispersive X-ray microanalysis, Room Temperature Photoluminescence & optical microscopy confirmed bonding of several mm2 of crack-free wurtzite GaN films onto a soda lime glass microscope slide with no obvious deterioration of the GaN morphology. Using such an approach, InGaN based devices can be lifted-off expensive single crystal substrates and bonded onto supports with a better cost-performance profile. Moreover, the approach offers the possibility of reclaiming and reusing the substrate.

Metal-semiconductor-metal solar blind ultraviolet photodetectors have been fabricated using both BGaN-GaN and BGaN-AlN superlattices as active layers. A high internal gain (up to 3 × 10 4 for optical power in the nW range) is obtained with a highly reduced dark current thanks to the boron incorporation. In the high optical power regime (W range), the time response is in the nanosecond range, which is much smaller than that of GaNand ZnO-based ultraviolet photodetectors. Moreover, the boron incorporation in GaN material allows the tuning of the cutoff wavelength.

In this paper we demonstrate a solution to systematically obtain thick, single phase InGaN epilayers by MOVPE. The solution consists in periodically inserting ultra-thin GaN interlayers during InGaN growth. Measurements by HAADF-STEM, X-ray diffraction, cathodoluminescence and photoluminescence demonstrate the effective suppression of the three-dimensional sublayer that is shown to spontaneously form in control InGaN epilayers grown without this method. Simulation predicts that tunneling through the GaN barriers is efficient and that carrier transport through this semi-bulk InGaN/GaN structure is similar to that of bulk InGaN. Such structures may be useful for improving the efficiency of InGaN solar cells by allowing thicker, higher quality InGaN absorption layers.

International audience; Large internal gains that can be obtained in wide band gap semiconductors-based (GaN and ZnO types) Schottky and/or metal-semiconductor-metal photodetectors are generally accompanied by large dark current and time response. We show that, using quasi-alloy of BGaN/GaN superlattices as the active layer, the dark current can be lowered while maintaining high internal gain (up to 3 x 10(4)) for optical power in the nW range and low time response (few tens of ns) for optical power in the W range. Furthermore, the boron incorporation allows the tuning of the cutoff wavelength

Based on current voltage (I—Vg) and capacitance voltage (C—Vg) measurements, a reliable procedure is proposed to determine the effective surface potential Vd(Vg) in Schottky diodes. In the framework of thermionic emission, our analysis includes both the effect of the series resistance and the ideality factor, even voltage dependent. This technique is applied to n-type indium phosphide (n-InP) Schottky diodes with and without an interfacial layer and allows us to provide an interpretation of the observed peak on the C—Vg measurements. The study clearly shows that the depletion width and the flat band barrier height deduced from C—Vg, which are important parameters directly related to the surface potential in the semiconductor, should be estimated within our approach to obtain more reliable information.

Light emission from a p-n junction biased in avalanche breakdown has been modeled over the range 1.4–3.4 eV. The model emphasizes indirect interband processes and Si self-absorption. Comparisons between measured and simulated spectra for sample junctions from multiple devices demonstrate that the model is simple, accurate, and consistent with fundamental physical device characteristics.

Electroluminescence (EL) measurements are used as a sensitive technique for the study of fast neutron irradiation of silicon n-channel JFET overlaid by a passivation oxide layer. By theoretical simulations, it is demonstrated that neutron irradiation result in two effects: an increase of the refractive index of the passivation oxide and the introduction of deep level traps which reduce the emitted intensities by reduction of the mobility of hot carriers.

International audience; Some properties of solar concentrator based on a Fresnel lens, a compound parabolic concentrator (CPC) and a cone are investigated. The effect of the source incidence angle on the focal point of the lens is highlighted and a procedure for a cone design is presented. This later defines also the sizes of the primary optic