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International audience; The Covid-19 crisis has led to a massive surge in the use of surgical masks worldwide, causing risks of shortages and high pollution. Various decontamination techniques are currently being studied to reduce these risks by allowing the reuse of masks. In this study, surgical masks were washed up to 10 times, each cycle under the same conditions. The consequences of the washing cycles on the structure, fiber morphology, and surface chemistry have been studied through several characterization techniques: scanning electron microscopy, wetting angle measurements, infrared spectroscopy, X-ray diffraction, and X-ray photoelectrons spectroscopy. The washing process did not induce large changes in the hydrophobicity of the surface, the contact angle remaining constant throughout the cycles. The composition observed in the IR spectrum also remained unchanged for washed masks up to 10 cycles. Some slight variations were observed during X-ray analysis: the crystallinity of the fibers as well as the size of the crystals increases with the number of wash cycles. The XPS analysis shows that after 10 cycles, the surface of the masks underwent a slight oxidation. In the SEM images, changes were observed in the arrangement of the fibers, which are more visible the more times the mask has been washed: they align themselves in bundles, form areas with holes in the mask layer, and are crushed in some areas.

International audience; Schottky barrier diodes on GaN on GaN substrates are fabricated for the purposeof material and technology characterization. The epitaxial layers are grown byMOCVD. I–V measurements as a function of the temperature in the range80–480 K show ideality factor (n) and barrier height (ϕB) variations not following athermionic (TE) model. Consequently, barrier height fluctuations are considered.In the temperature range 280–480 K, an average barrier height of 1.31 eV with arelatively large standard deviation (σ) of 0.15 eV is extracted using this model. Then(T ) variation is also analyzed in order to extract the field sensibility of 1) themean barrier height variation (ρ2 = -0.1) and 2) the barrier height standarddeviation (ρ3 = -15mV). The corrected Richardson plot usingϕB and σ values islinear and gives a Richardson constant of 31.5 A cm² K² close to the theoreticalvalue of 26.4 A cm² K². For a deeper understanding of ϕB fluctuation origins,micro-Raman mapping of the epitaxial layers and deep-level transient spectroscopy(DLTS) are used. μ-RS mappings show compressive strain for diodeshaving suffered electrical breakdown. DLTS analysis shows the presence of ninelevels whose signatures are extracted and nature discussed.

The current–voltage (I–V) characteristics of Schottky diodes on free-standing GaN substrate are investigated by using electrical characterization and analytical modelling calculation. We have calculated the electrical parameters from experimental current-voltage curve by two methods: ln(I) and Cheung. So, we calculated different electrical parameters using experimental I-V curve such as saturation current, ideality factor, series resistance and barrier height. We have found from the first method, the ideality factor n (1.02), the barrier height fb (0.65 eV) and a series resistance Rs (84 Ω). From the second method, we have found, n (1.09), fb (0.79 eV) and Rs (79.58 Ω - 79.73 Ω). Using analytical approach, we plotted the theoretical curves for comparison with the experimental characteristic and also to determine the dominant current transport mechanism. The results found support an assumption that the dominant current mechanism in Au/n-GaN (free-standing substrate) Schottky diode is the thermionic current.

We report the enhancement of the optical emission between 850 and 1400 nm of an ensemble of silicon mono-vacancies (VSi), silicon and carbon divacancies (VCVSi), and nitrogen vacancies (NCVSi) in an n-type 4H-SiC array of micropillars. The micropillars have a length of ca. 4.5 μm and a diameter of ca. 740 nm, and were implanted with H+ ions to produce an ensemble of color centers at a depth of approximately 2 μm. The samples were in part annealed at different temperatures (750 and 900 °C) to selectively produce distinct color centers. For all these color centers we saw an enhancement of the photostable fluorescence emission of at least a factor of 6 using micro-photoluminescence systems. Using custom confocal microscopy setups, we characterized the emission of VSi measuring an enhancement by up to a factor of 20, and of NCVSi with an enhancement up to a factor of 7. The experimental results are supported by finite element method simulations. Our study provides the pathway for device design and fabrication with an integrated ultra-bright ensemble of VSi and NCVSi for in vivo imaging and sensing in the infrared.

International audience; Irradiating porous silicon is expected to reduce thermal conductivity without altering the porous structure and can be studied by optical techniques provided optical properties can be established reliably. Toward this end, meso-porous silicon (PSi), with a porosity of 56%, was prepared from p + Si wafer (0.01-0.02 .cm-1 resistivity) and was partially amorphized by irradiation in the electronic regime with 129 Xe ions at two different energies (29 MeV and 91 MeV) and five fluences ranging from 10 12 cm-2 to 3.10 13 cm-2. The PSi structure is monitored by scanning electron microscopy. High-resolution transmission electron microscopy shows that the amorphous phase is homogeneous in volume and that there is no formation of amorphous-crystalline core-shell structures. An agreement is found between the thermal conductivity results obtained with micro-Raman thermometry, which is an optical contactless technique heating the sample in the depth, and scanning thermal microscopy, which is an electrical technique heating the sample by contact at the sample surface. A linear relation is established between the effective thermal conductivity and the amorphous fraction, predicting the thermal conductivity of fully-amorphous porous Si below 1 W.m-1 .K-1. The obtained values are comparable to that of SiO2, reduced by a factor 6 in comparison to non-irradiated porous samples (~6.5 W.m-1 .K-1) and smaller than bulk silicon by more than two orders of magnitude.

We report the characterization of arrays of micropillars fabricated in an n-type 4H-SiC using photolithography to enhance the emission of bandgap color centers in silicon carbide emitting in the spectral region from 850 nm to 1400 nm. The emission is identified by the mono-vacancy of Si (VSi), silicon and carbon divacancy (VCVSi), and the nitrogenvacancy (NCVSi) using low-temperature micro-photoluminescence. These emitters are created in large ensemble by using ions implantation and annealing at a different temperature to extend the emission in the O-band region. The optical fluorescence enhancement experimental results are obtained using custom made IR confocal microscope to measure integrated PL of up to a factor of 20 compared to bulk material. This enhancement is supported by finite-element simulations considering the non-unity quantum efficiency of the emitters and their broad spectral emission at room temperature. Our study provides the pathway for quantum sensing device design and fabrication with an integrated ultrabright emission for in vivo imaging in the infrared.

International audience; A new in situ technique for temperature and pressure measurement within dynamic thin-film flows of liquids is presented. The technique is based on the fluorescence emission sensitivity of CdSe/CdS/ZnS quantum dots to temperature and pressure variations. In this respect, the quantum dots were dispersed in squalane, and their emission energy dependence on temperature and pressure was calibrated under static conditions. Temperature calibration was established between 295 K and 393 K showing a temperature sensitivity of 0.32 meV K−1. Pressure calibration was, in turn, conducted up to 1.1 GPa using a diamond anvil cell, yielding a pressure sensitivity of 33.2 meV GPa−1. The potential of CdSe/CdS/ZnS quantum dots as sensors to probe temperature and pressure was proven by applying the in situ technique to thin films of liquids undergoing dynamic conditions. Namely, temperature rises have been measured in liquid films subjected to shear heating between two parallel plates in an optical rheometer. In addition, pressure rises have been measured in a lubricated point contact under pure rolling and isothermal conditions. In both cases, the measured values have been successfully compared with theoretical or numerical predictions. These comparisons allowed the validation of the new in situ technique and demonstrated the potential of the quantum dots for further mapping application in more complex and/or severe conditions.

International audience; In past few years, point defects in silicon carbide (SiC) have been identified as promising for applications in quantum technologies [1]. A variety of point defects in hexagonal SiC [2], including VSi and VSiVC have been optically isolated and used as single defect-based spin qubits with long coherence time [3-5]. All of this, proves that these point defects allow the SiC to be a very favorable candidate for quantum applications especially, solid state quantum bits (Qubits) and single photon source (SPS). Most of these studies were carried out on the hexagonal polytypes 4H-SiC and 6H-SiC, although the 3C-SiC polytype presents the unique advantage of integration possibility on standard Si wafer. This is due to the amount of defects (dislocation mainly) in the 3C-SiC heteroepitaxy on Si which are detrimental for long coherence time considering Qubit application. Consequently, the goal of the present study is the investigation of point defects formation after implantation by proton H + (300 keV) and irradiation by electron e-(0.8 and 2 MeV) in 3C-SiC (respectively 3C-SiC and 3C-SiC) for SPS application purpose. Toward this end, we have combined two characterization techniques, the photoluminescence (PL) and the electron paramagnetic resonance (EPR). PL (12K) and EPR (70-300K) measurements will be presented in order to analyze precisely the signatures of point defects generated after these two types of irradiations. The effects of the thermal annealing (500-1000°C) were also investigated. PL spectra both for 3C-SiC and 3C-SiC are presented in figure 1 for the annealing temperatures giving the highest PL signal (1000°C for 3C-SiC and 750°C for 3C-SiC). We notice first that the whole PL signal is higher for 3C-SiC. In this case the spectrum is dominated by the DI defect line (possibly related to antisite pair [6]) and the E line (attributed to Si vacancy [7, 8]) while in electron irradiated sample the  line (attributed to CSiVC in a 3C-SiC nanocrystal [8]) dominates as previously reported [9]. A strong zero phonon line at 1.6 eV also appears for 3C-SiC with its phonon replica. This line was previously observed also for neutron and proton irradiated 3C-SiC and at present is of unknown origin [10, 11]. In the infrared range, the proton implantation is also more efficient to produce the VcVsi PL line with an optimum luminescence for 750°C annealing. All together, these results show that, even if the energy transferred to the host atoms during electron irradiation is quite above the displacement thresholds for both C and Si, defects involving Si vacancy are more pronounced in 3C-SiC samples. EPR spectra for 3C-SiC for isochronal annealing (30 min.) at different temperatures are presented in figure 2. The spin-three-half negatively-charged Si vacancy (the T1 center) is a dominant defect in 3C-SiC epitaxial layers corresponding to the E line in the PL spectra. Similar to neutron irradiated 3C-SiC crystals the as-implanted not annealed 3C-SiC samples demonstrate an isotropic spectrum with the g-value of 2.0029 and a superhyperfine doublet with a splitting typical to the T1 center

International audience; By thermally characterizing nanometer-thin suspended silicon membranes with various micrometric lengths in ambient conditions, we determine simultaneously the spatial resolution of our Wollaston-probe scanning thermal microscopy experiment, which probes an area of (285 nm)2, and the effective thermal conductivity of the membranes of 40 W.m-1.K-1. This value is smaller thanthe in-plane thermal conductivity measured using other techniques in vacuum (60 W.m-1.K-1), revealing that both cross-plane and in-plane heat conduction are strongly affected by the native oxide in ambient conditions. This work also underlines that high-thermal conductivity samples can be characterized by scanning thermal microscopy when micro-patterned.

In this paper, thermal transport properties study of partially amorphous porous silicon obtained by irradiation with swift (110 MeV) uranium ions is reported. A photoacoustic technique allows thermal conductivity evaluation of the samples with enhanced amorphous fraction (>80%). In particular, 3-fold thermal conductivity decrease is shown to be achieved for the completely amorphous porous silicon layers in comparison with as-prepared non-irradiated porous samples.

In this paper, we have studied the Schottky contact of two structures AlInN/GaN and AlGaN/GaN in transistors HEMTs. The current–voltage Igs(Vgs) of AlInN/GaN and AlGaN/GaN structures were investigated at room temperature. The electrical parameters such as ideality factor (2.3 and 1.96), barrier height (0.72 and 0.71 eV) and series resistance (33 and 153 $$\Omega $$ ) were evaluated from I–V data. The comparison of the performance of the two structures AlInN/GaN and AlGaN/GaN in transistors HEMTs have been analyzed and discussed.

The photoluminescence properties of silicon nanoparticles ''Si NPs'' have their application as fluorophore in the field of biology . Their use as probes in lubricated contacts is very promising because of their resistance to mechanical stresses and harsh environment. A top-down technology, electrochemical anodization, is used for the development of these NPS. Their size selection is obtained by centrifugation. The surface functionalization of these NPs is an essential step for their dispersion in non-polar liquids. The main results of photoluminescence as a function of temperature are presented.

This work analyses the heat transfer between various scanning thermal microscopy (SThM) probes and samples. In order to perform quantitative measurements with SThM techniques, we have developed well-established and reproducible calibration methodologies. We present here two approaches of the SThM measurement: one to measure thermal conductivity of solid materials with a Wollaston SThM microprobe and a second one to evaluate phase transition temperatures of polymeric materials with a silicon low-doped nanoprobe. Based on the comparison of experimental data and modeling results, we have estimated the local resolution of the microprobe to be associated to a radius of 300 nm. Concerning the nanoprobe, we have demonstrated the strong dependence of measurement on sample topography and roughness.

Intense visible nano-emitters are key objects for many technologies such as single photon source, bio-labels or energy convertors. Chalcogenide nanocrystals have ruled this domain for several decades. However, there is a demand for cheaper and less toxic materials. In this scheme, ZnO nanoparticles have appeared as potential candidates. At the nanoscale, they exhibit crystalline defects which can generate intense visible emission. However, even though photoluminescence quantum yields as high as 60% have been reported, it still remains to get quantum yield of that order of magnitude which remains stable over a long period. In this purpose, we present hybrid ZnO/polyacrylic acid (PAAH) nanocomposites, obtained from the hydrolysis of diethylzinc in presence of PAAH, exhibiting quantum yield systematically larger than 20%. By optimizing the nature and properties of the polymeric acid, the quantum yield is increased up to 70% and remains stable over months. This enhancement is explained by a model based on the hybrid type II heterostructure formed by ZnO/PAAH. The addition of PAAX (X = H or Na) during the hydrolysis of ZnEt2 represents a cost effective method to synthesize scalable amounts of highly luminescent ZnO/PAAX nanocomposites.

Optically active point defects in SiC are attracting a growing interest thanks to their prospect of emission in the near-infrared (NIR) spectral region (application in optical fiber communications and for in vivo imaging) and also thanks to the possibility to control optically their spin. Most of the results have been obtained for the hexagonal SiC polytypes. In this work, we focus on the optical properties of point defects in the 3C-SiC polytype after ion implantation. Different ions, fluences and post-implantation annealing were performed to optimize the defect formation. Photoluminescence results show that the optimal conditions for intense D1 defect related PL emission in the 600-850 nm range are high temperature annealing (up to 1200 °C) and a displacement density not exceeding 1020 cm-3 at the projected range. The creation of Ky5 defect at 1.12 eV has also been demonstrated for lower temperature annealing (800 °C). (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanowires with different nitrogen concentrations were grown by Metal-Organic Chemical Vapor Deposition (MOCVD) using DEZn, N2O and NH3as zinc, oxygen and nitrogen doping sources respectively. Low temperature photoluminescence, Raman spectroscopy and Transmission Electron Microscopy are combined to study the incorporation of nitrogen in the wires. The observation of donor-acceptor pair band confirms that the incorporation nitrogen in ZnO nanowires is responsible for the creation of acceptor centers. The additional peaks observed in Raman are correlated to nano-sized inter-atomic distance fluctuations observed in TEM. These domains combined with a resonance effect are probably the explanation of the huge Raman cross section observed for the impurity related peaks.

AlGaN/GaN high electron mobility transistors are investigated by DLTS measurements. 6 different are extracted with the following activation energies: 0.12 eV, 0.15 eV, 0.21 eV, 0.42 eV, 0.49 eV and 0.94 eV. Based on comparison with literature results and measurements as a function of the pulse reverse bias, the trap localisation in the structure is discussed. Additional measurements as a function of the filling pulse duration reveal the presence of decorated extended defects in the samples. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A simple and low-cost technological approach for the straining of thin crystalline silicon (Si) films using porous silicon (PS) as stress generating nanomaterial is reported. Firstly, a technological approach allowing fabrication of thin Si films on a bulk meso-PS substrate is described. Secondly, low temperature (

A computational model has been developed in order to explain the anomalies observed in the direct SiC-6H I(V) characteristic diode. These irregularities consist in a thermionic, a generation–recombination, a tunnelling and a leakage electric current contributions. Two kinds of diode's dimensions have been used. For the small one, a good fitting, at all temperatures has been obtained, but for the big one, the fitting was relatively bad, perhaps due to a so important parasite resistance versus potential variation. Even, a high parasite resistance has been encountered near room temperature. From the Richardson plot, it has been extracted a value of the Richardson constant A* very smaller than the theoretical value. A value of the barrier height has also been evaluated.

International audience; We report an optical study of 3C-SiC layers grown on 6H-SiC substrates by VLS mechanism using a Si-Ge melt. The photoluminescence and μ-Raman results show a clear and significant incorporation of germanium in the layers from the melt. A photoluminescence emission attributed to Ge related transitions is observed in the infrared region. μ-Raman spectra exhibit two peaks related to the Ge-Ge and Si-Ge bonds. From the characteristics of these Raman peaks, it was found that the amount of Ge incorporated inside the 3C layers increases with increasing Ge content of the melt. This has been verified by Particle-Induced X-rays Emission (PIXE) measurements which gave a Ge concentration varying from ~ 1x1019 to ~ 1x1020 at.cm-3. All these results suggest that Ge incorporates in the VLS grown 3C layers by forming Si-Ge-(C) nanoclusters.

Two models have been used in order to explain the anomalies observed in a Ni/SiC-6H Schottky n-type diode I(V) characteristic. Both, parallel conduction and potential fluctuation models showed that the barrier's height is around a mean value of 1.86V, corresponding to a factor of ideality of n=1. Another conclusion was that @f"B^i@?=@f"B^C=1.88V. It has been, also, explained why the Arrhenius or Richardson plot (ln(I"s/T^2) versus 1/T) is not linear and why the area of the low barrier height A"l, representing a defective zone, is approximately about 0.12% of the total area contact.

QuaSiC TM substrates can be obtained by transferring a single crystal SiC layer onto a poly SiC substrate using the Smart Cut TM technology. In order to overcome the difficulty of limited thickness, an important improvement has been demonstrated, which consists in obtaining thick SiC structure by growing epitaxial SiC layers on top of transferred layers. The aim of this work is a structural analysis of such layers by Transmission Electron Microscopy and Photoluminescence.

Vapor-Liquid-Solid was used for growing boron doped homoepitaxial SiC layers on 4HSiC( 0001) 8°off substrates. Si-based melts were fed by propane (5 sccm) in the temperature range 1450-1500°C. Two main approaches were studied to incorporate boron during growth : 1) adding elemental B in the initial melt, with two different compositions : Si90B10 and Si27Ge68B5; the growth was performed at 1500°C; 2) adding B2H6 (1 to 5 sccm) to the gas phase during growth with a melt composition of Si25Ge75; the growth was performed at 1450°C. In most cases, the growth time was limited by liquid loss due to wetting on the crucible walls. The longer growth duration (1h) was obtained when adding B2H6 to the gas phase. In the case of Si90B10 melt, the surface morphology exhibits large and parallel terraces whereas the step front is more undulated when adding Ge. Raman and photoluminescence characterizations performed on these layers confirmed the 4H polytype of the layers in addition to the presence of B which results in a strong B-N donor-acceptor band. Particle induced γ-ray emission was also used to detect B incorporation inside the grown layers.

We report an optical investigation of cubic Silicon Carbide (3C-SiC) layers grown on 6H-SiC substrates by Chemical Vapour Deposition and Vapour-Liquid-Solid mechanism. Micro- Infrared reflectance ('-IR), micro-Raman ('-Raman) and low temperature photoluminescence spectroscopies were used for the characterisation of such layers. '-IR measurements showed unusual optical behaviour of 3C-SiC layers. The difference of refraction index between the 3C-SiC film and the 6H-SiC substrate cannot explain this result. The experimental '-IR reflectance spectrum was modelled by introducing a thin (thickness ≤ 0.5 'm) metallic-like (doping ≥ 1020 at.cm-3) interfacial film between the layer and the substrate. The photoluminescence spectra revealed the presence of a peak which may be attributed to recombination at the 3C/6H interface. All these results suggest the presence of a two dimensional electron gas at the interface.

Photoluminescence properties of a freestanding nanoporous SiC layer obtained from bulk 6H-SiC substrate as well as SiC nanopowder consisting of numerous separated nanoparticles has been investigated. The nanoporous SiC layer is obtained by UV radiation assisted electrochemical etching of the 6H-SiC wafer and the SiC nanopowder is formed by mechanical grinding of the nanoporous SiC free layer. A comparison of low temperature PL spectra of the SiC nanostructures and initial SiC bulk substrate has been performed. The evolution of PL spectra of the SiC nanostructures with respect to their surface states and excitation laser power has been studied. In particular, the well pronounced high energy tail above the excitonic bandgap in the PL spectra of the nanostructured SiC is attributed to quantum confinement effects. The strong PL signal obtained below the bandgap is explained by radiative transitions involving surface states, N-Al donoracceptor recombination levels and deep levels corresponding to volume defects in the SiC nanocrystallites.

International audience; Degenerate metal oxide nanoparticles are promising systems to expand the significant achievements of plasmonics into the infrared (IR) range. Among the possible candidates, Ga-doped ZnO nanocrystals are particularly suited for mid IR, considering their wide range of possible doping level and thus of plasmon tuning. In the present work, we report on the tunable mid IR plasmon induced in degenerate Ga-doped ZnO nanocrystals. The nanocrystals are produced by a plasma expansion and exhibit unprotected surfaces. Tuning the Ga concentration allows tuning the localized surface plasmon resonance. Moreover, the plasmon resonance is characterized by a large damping. By comparing the plasmon of nanocrystals assemblies to that of nanoparticles dispersed in an alumina matrix, we investigate the possible origins of such damping. We demonstrate that it partially results from the self-organization of the naked particles but also from intrinsic inhomogeneity of dopants.

Our work is focused on the identification of defects responsible for current fluctuations at the origin of low frequency noise or random telegraphic signals in 4H-SiC MESFETs on semiinsulating (SI) substrates. We show that devices having instabilities have DC output characteristics with random discrete fluctuations of the drain current. The RTS noise parameters analysis (amplitude, high and low state time durations) as a function of temperature and bias voltage provides the signature of the involved traps (activation energy and cross section both for emission and capture). From the power spectral density of the drain current noise (PSD) we have measured the cut-off frequency of a single trap even at very low frequencies (from 0.1 Hz) and we propose that the noise responsible of RTS fluctuations is a generation-recombination noise. Finally, it is shown that the frequency analysis of the random telegraphic signal is a well-suited tool for the study of single defects in very small devices.

SiC nanopowder has been formed using an original technological approach based on grinding of bulk porous SiC nanostructures. The initial porous SiC nanostructures were obtained by anodization of n+-type 4H-SiC substrate in HF/Ethanol solution under UV illumination. Large single SiC nanoparticles (~ 30 nm in diameter) constituting the nanopowder have a porous structure which can be clearly visible. On the other hand, small single SiC nanoparticles (~ 4 nm in diameter) exhibit a clear crystalline structure. A broad and very intense luminescence band (400 – 900 nm) provided from the nanopowder corresponds to the radiative processes involving nanoparticle surface states. A smaller photoluminescence peak centred at 358 nm may correspond to radiative recombination of the photogenerated excitons confined in the individual and spatially separated 4HSiC nanoparticles.

Conductance deep-level transient spectroscopy (CDLTS) has been performed for 4H-SiC metal–semiconductor field effect transistor (4H-SiC MESFETs). Additionally to an emission band, two unexpected hole-like traps labelled HL1 and HL2 are observed in the spectra. Different measurements, varying the bias conditions show that these traps originate either from the surface state outside the gate region between gate and drain electrodes (HL1) or from interface states at the channel/buffer-layer or buffer-layer/semi-insulating substrate (HL2). The activation energies of both states are respectively determined as 0.90 eV for HL1 and 0.56 eV for HL2.

Conductance DLTS measurements have been performed on 4H-SiC MESFETs. A broad band due to electron emission by different levels is observed. An additional “hole-like” level with activation energy of 0.9 eV is obtained in linear regime but not in saturation regime. From the results, it is proposed that this “hole-like” signal is due to capture of electron present at a conductive SiC/SiO2 interfacial layer.

UV scanning photoluminescence spectroscopy is applied to 4H-SiC epitaxy characterization. In a first part, the technique is used for triangular defects characterization. The results show that two kinds of defects are present. Some defects are inclusion of cubic SiC which is confirmed by Raman spectroscopy. The other ones consist of staking faults of different thicknesses acting as quantum wells. In a second part, the effective lifetime profile is mapped for a whole 50 mm epitaxy using the variation of room temperature PL intensity versus excitation intensity.

In this paper we present static measurements fand defects analysis performed on 4H-SiC MESFETs on semi-insulating (SI) substrates containing vanadium. I d-Vds -T and I d-Vgs -T characteristics show anomalies (Threshold voltage shift, leakage current, degradation in saturation current...). Deep defects analysis performed by capacitive transient spectroscopy (C-DLTS) proves the presence of one deep defect called E1 with an activation energy 0.32eV. The studies of C-DLTS signal with pulse duration (t p) and polarization voltage (V r) confirm that E 1 trap is a point defect. Current transient spectroscopy (I-DLTS) performed in the same devices confirm E1 defect and shows the presence of six levels with activation energies ranging from 0.09eV to 1.01eV. The localization and the identification of these defects is presented. Finally, the correlation between the anomalies observed on output characteristics and defects is discussed.

The low channel mobility in N-MOS 4H-SiC transistor is a major key issue for the development of power devices with satisfactory on state characteristics. Previous works have demonstrated that this low channel mobility is due to high interface state density (Dit) near the conduction band edge. Furthermore, the realization of SiC MOSFETs sustaining high reverse field necessitates thick epitaxial layer growth. An important thickness (> 30 gm) unfortunately involves important surface roughness which may result in a high interface trap density (Dit) and surface potential fluctuation (sigma(s)) at the SiC/SiO2 interface. In this study, we focus on SiO2/SiC MOS interface quality characterization as a function of process conditions and material properties (dopant type, thick layer growth technique). Investigations of the oxide quality on thick layers grown by CVD and PVT has been realized using CV under UV lightening and GV techniques. We evidenced that the Dit value (between 10(10) cm(-2).eV(-1) and 9x10(10) cm(-2).eV(-1) from 0.9 Ev to 0.2 eV below Ec) and sigma(s) value (60 mV) were slightly lower for thick PVT layers. A discrepancy in the Dit values obtained from C-V and G-V measurements is attributed to the large surface potential standard deviation. Results from an original oxide growth process using a deposited sacrificial silicon layer under UHV conditions are also presented.

International audience; 4H-SiC epilayers have been achieved by cold wall CVD in the silane-propane system between 1450°C and 1600°C. The layers have been characterized by AFM, Raman spectroscopy, low temperature photoluminescence (LTPL) and CV measurements. The layers are mirror-like and present a low density of sharp triangular defects. The average defect density is 104 per cm2. A growth rate of 6 μm.h-1 is obtained at 1600°C. A residual doping level of 4.1014 cm-3 is obtained for a C/Si ratio of ten. When the C/Si ratio is further increased (>18), a degradation of the layer morphology is observed.

In this work, a method to obtain the Shockley-Read-Hall (SRH) minor ity carrier lifetime from the room temperature photoluminescence intensity is proposed. Indeed, taking into ac count the different recombination mechanisms, we calculate the photoluminescence (PL) intensity as a function of carrier lifetime. The PL map can then be converted in l ifetime map. An example for a 4H-SiC epitaxy is given. The obtained values ranging from 20 ns t o 150 ns are in good agreement with typical values reported in the literature.

An UV scanning photoluminescence (SPL) equipment has been developed in order to study both structural defects at a microscopic scale and the homogeneity of physical properties at the wafer scale in silicon carbide. In one hand, the optical signature of micropipes, screw dislocation and triangular defects are presented. In most of the cases the SPL signal decrease for micropipes because of the defect geometry. In the case of dislocation, a signal exhaust in the neighbourhood of the defect is observed and attributed to the gettering effect of non radiative traps at the immediate vicinity of the defect. For triangular defects, we tentatively ascribe the PL spectra observed to Shockley stacking faults. In the other hand, a method to obtain the minority carrier lifetime mapping from the integrated PL signal is described. The mapping of this parameter is of prime interest both for the material quality control and for bipolar device's development.

This work demonstrates that the "purity", meaning the low density of electron traps in a semi-insulating (SI) SiC substrate, can be crucial for the electrical characteristics of 4H-SiC MESFETs. Structures realized on two types of SI substrates have been investigated. The first kind is vanadium doped substrates grown by the classical Physical Vapor Transport (PVT) sublimation technique. The second kind are extremely low vanadium content SI substrates grown by the high temperature CVD (HTCVD) technique. For all the transistors, I/sub d/-V/sub ds/ measurements have been performed as a function of temperature. Different parasitic effects have been observed on the static output characteristics in the case of PVT substrates. Frequency dispersion measurements of the transconductance and drain-source output conductance, have next been realized. The results give clear evidence of the presence of deep traps in the transistors realized on PVT substrates. Those traps have an activation energy of 1.05 eV and a capture cross section between 10/sup -18/ cm/sup -2/ and 10/sup -19/ cm/sup -2/. They are most probably related to vanadium. The correlation between the presence of these traps and the parasitic effects on the output characteristics is discussed and the trap localization in the structure is established. In the case of HTCVD very low vanadium substrates, no parasitic effect have been observed and the presence of traps was not detected by the different characterization techniques.

We have adapted a scanning photoluminescence (SPL) apparatus, previously developed for III-V compounds analysis, for the characterization of SiC. The PL mapping is obtained by scanning the sample, fixed to an x - y stage with 1 μ m minimal step, under a doubled Ar + laser beam (244 nm) focused by a microscope objective (×52). For this excitation the spot diameter is about 4 μ m. The PL signal can be either directly detected, giving integrated PL intensity, either dispersed using a monochromator, giving spectrally resolved PL (1 nm resolution). The measurements can be realized at room temperature for near band edge studies, or at low temperature (80 K) for deep defects investigation. The gettering effect of non radiative centres by the screw dislocations in 6H-SiC is evidenced using this apparatus.