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In this paper, we studied the electrical characteristic of Schottky diodes based on gold contact on nitridated GaAs substrates. The used (100) GaAs substrate is n-type with concentration of Nd = 4.9 × 1015 cm–3. Nitridation process was performed using a N2 glow discharge source (GDS) creating N atomic species. A ultra-thin film with a thickness of 2.2 nm GaN is performed on GaAs surface. In order to study the electric characteristics under illumination, we use of a He–Ne laser of 1 mW power and 632.8 nm wavelength. The current–voltage (I–V) of the Au/GaN/GaAs structures was investigated at room temperature. The saturation current IS, the series resistance RS and the mean ideality factor n are, respectively, equal to 4.46 × 10–07 A, 172 Ohm, 1.4 in the dark and to 5.64 × 10–07 A, 148 Ohm, 1.21 under illumination. To analyze these results, a 1D-simulation code of forward and reverse current–voltage characteristics versus the critical parameters of a nitridated GaAs Schottky diode is implemented. The algorithm is based on the solution of the system composed by Poisson’s and continuities equations. In this calculation, we take into account the existence of the GaN layer and the localization of traps states in the perturbed interface. We have considered the W-shaped and U-shaped distribution of traps states in the band gap. The effects of the doping concentration of GaAs, the traps states density, light intensities and the work function of gold $${{\phi }_{m}}$$ are investigated. By fitting the experimental curve, we can deduce the values of the traps states and the exact value of the work function of gold, and consequently we validate the developed model.

The aim of the present work is to perform Attenuated Total Reflectance-Fourier Transform Infra-Red spectroscopy (ATR-FTIR) investigations during N2 plasma treatment of GaAs surfaces at 500 °C inside an UHV chamber using the high intensity light of SOLEIL synchrotron at SMIS beamline. Moreover this work uses the complementarities of Density Functional Theory (DFT) normal-mode frequency calculations with ATR-FTIR measurements to assist in the assignment of vibrations involving bonds to nitrogen atoms, especially by rendering the GaN layer partially amorphous (by removing the crystal symmetry constraint, using Car Parrinello dynamics to simulate annealing in geometry optimization). s and p polarizations were used to study the evolution of the different GaN vibrations during the nitridation of GaAs for two surface orientations (0 0 1) and (1 1 1)B. Results show that normal stretch vibrations are always detected at the same frequency matching the DFT calculated values very well, whereas other vibration modes (bridge symmetric and asymmetric stretches for (0 0 1) GaAs and tripod symmetric and asymmetric stretches for (1 1 1)B GaAs) induced by the non-crystallinity of the GaN layer exhibit variable frequencies. Furthermore evolutions of these frequencies with the nitridation time provide much information on bond creations, especially at the very beginning of the process.

Two kinds of N2 plasma source, ECR (electron cyclotron resonance) and GDS (glow discharge source) generating mostly N-radical atoms and N-cationic species respectively, were used to grow a thin nitride layer on a GaAs(100) substrate. It was found that this nitridation followed by annealing at 620 °C permits the crystallization of the nitride layer. Pyramidal Zinc Blende GaN nanostructures (zb-GaN) with four facets were obtained using GDS plasma. Surprisingly, a planar and pure wurtzite structure (w-GaN) was obtained using the ECR source. This w-GaN structure shows low photoluminescence intensity and a biaxial tensile strain due to lattice mismatch. Accordingly, the operator can select which phase is formed, simply by switching plasma source. The valence band discontinuity ΔEv has been determined to be 1.74 eV for the zb-GaN/GaAs and w-GaN/GaAs junctions by X-ray photoelectron spectroscopy. As a consequence the conduction bands of the GaAs substrate and the elaborated GaN thin layer are aligned for a zb-GaN/GaAs junction giving efficient electron transport at the zb-GaN/GaAs interface. For w-GaN/GaAs junction, the conduction band discontinuity ΔEc is 0.23 eV inducing an electron confinement in the GaAs(100) which can be an effective way to improve the electronic or optical properties of GaAs devices.

The high density of interface and surface states that cause the strong Fermi pinning observed on GaAs surfaces can be reduced by depositing GaN ultra-thin films on GaAs. To further improve this passivation, it is necessary to investigate the nitridation phenomena by identifying the distinct steps occurring during the process and to understand and quantify the growth kinetics of GaAs nitridation under different conditions. Nitridation of the cleaned GaAs substrate was performed using N 2 plasma source. Two approaches have been combined. Firstly, an AR-XPS (Angle Resolved X-ray Photoelectron Spectroscopy) study is carried out to determine the chemical environments of the Ga, As and N atoms and the composition depth profile of the GaN thin film which allow us to summarize the nitridation process in three steps. Moreover, the temperature and time treatment have been investigated and show a significant impact on the formation of the GaN layer. The second approach is a refined growth kinetic model which better describes the GaN growth as a function of the nitridation time. This model clarifies the exchange mechanism of arsenic with nitrogen atoms at the GaN/GaAs interface and the phenomenon of quasi-saturation of the process observed experimentally.

International audience; This study reports a synthesis by the sol-gel method of stable and size-controlled ZnO quantum dots (QDs) embedded into a SiO2 matrix in the diameter range of 2.7-5.5 nm with strong visible emission in the blue-green region. X-ray diffraction and selected area electron diffraction techniques evidence a wurtzite structure of the prepared ZnO QDs. Transmission electron microscopy investigation highlights that the ZnO nanoparticles produced in methanol solution have a nonuniform shape. Addition of tetraethyl ortho-silicate (TEOS) in the solution at different times blocks the nucleation of the QDs and allows the control of the QD size due to a SiO2 capping. Moreover, Fourier transformed infrared analysis and X-ray photoelectron spectroscopy (XPS) were used to show the ZnO QD composition and to confirm their incorporation into the SiO2 matrix by the creation of a Zn-O-Si crossing link. A strong UV band and a weak visible band are revealed at room temperature by photoluminescence (PL) measurement for pure ZnO nanoparticles, whereas, when TEOS is added, the UV band is quenched and a strong visible emission in the range 400-650 nm is enhanced. PL spectra fitting, using Gaussian curves, shows three possible transitions that induce the visible emission. This PL study is correlated to the quantitative XPS study combined with a simple model describing the nanoparticles giving the relative amount of species involved in this emission mechanism. These QDs are then used to manufacture humidity sensors. Indeed, electrical measurements show a high sensitivity to the relative humidity. Moreover, a remarkable enhancement of the sensor performance is observed when the ZnO QD size decreases.

The electronic properties of n-type InP epitaxial layers covered by their native oxides have been investigated in order to explain the NO 2 gas sensing mechanism. The impact of interface states on the interface Fermi level, E F , carrier concentration in-depth profiles, n ( x ), and resistance, R , of n-InP layers has been studied by means of numerical analysis. The U-shaped interface state continuum, with the density minimum, N SS0 , from 10 10 to 10 13 eV −1 cm −2 , has been assumed at the InP interface according to the disordered-induced gap state model. Moreover, the surface fixed charge, Q FC , representing adsorbed ions at the semiconductor surface has been introduced. Also the influence of temperature on the electron distribution n ( x ) has been analysed. The n-InP layer resistance and Hall-effect measurements (using the Van der Pauw method) have been performed for the InP sensors before and upon NO 2 action in order to assess the influence of gas adsorption on the electron concentration and mobility as well as on the depletion layer width, W . On this basis the influence of interface states and near-surface region on the InP layer response to NO 2 adsorption has been determined. In addition, the conclusions for optimising the InP-based resistive sensor structure (in terms of the layer thickness and doping) have been obtained.

The benefits of using a low power glow discharge nitrogen plasma source to create high quality GaN layers on GaAs(001) surface are first highlighted. This uncommon type of plasma source has the particularity of working at a low power (3–10 W) and a low pressure (10 − 1 Pa) which induce creation of a small quantity of active nitrogen species. We put in evidence that this distinctiveness allows the growth of a stoichiometric and As-free GaN ultra-thin film on a GaAs(001) substrate by the mean of the inter-diffusion of As and N atoms. XPS, EELS, AFM are used to monitor surface composition and structure changes and to estimate the GaN thickness. A near saturation of the nitride layer thickness versus plasma exposure time is found. Furthermore, the possibility to crystallize the amorphous GaN layer by an annealing at 620 °C in a cubic structure with a lattice parameter close to that of c-GaN is put in evidence by means of TEM and LEED measurements. These measurements also show the homogeneity of the GaN thickness. In addition, the passivating effect of the GaN ultra-thin film to protect the GaAs surface is proved with the monitoring by XPS of the surface oxidation during several days of air exposure.

An in situ method based on the combination between XPS and MM-EPES techniques is developed in order to study the growth mode and to determine the nanostructure surface of a deposited ultra thin film on solid substrate by determining both the thickness and the covering. In this way, XPS and MM-EPES modeling are done by adapting a simple approach of the surface organization. Then this method is used to study a gold film deposition on an oxidized silicon substrate. This study leads to determine accurately the surface organization and thus the growth mode. Moreover, the obtained results were validated by performing microscopic measurement by Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). AFM and SEM results show a good agreement with those determined by the combination of XPS and MM-EPES techniques. Moreover, experiment shows that this method is able to determine surface parameters when the microscopy techniques do not give any information in the case of a small quantity of deposited Au.

The aim of the present study is to demonstrate the feasibility to form well-ordered nanoholes on InP(1 0 0) surfaces by low Ar + ion sputtering process in UHV conditions from anodized aluminum oxide (AAO) templates. This process is a promising approach in creating ordered arrays of surface nanostructures with controllable size and morphology. To follow the Ar + ion sputtering effects on the AAO/InP surfaces, X-ray photoelectron spectroscopy (XPS) was used to determine the different surface species. In 4d and P 2p core level spectra were recorded on different InP(1 0 0) surfaces after ions bombardment. XPS results showed the presence of metallic indium on both smooth InP(1 0 0) and AAO/InP(1 0 0) surfaces. Finally, we showed that this experiment led to the formation of metallic In dropplets about 10 nm in diameter on nanoholes patterned InP surface while the as-received InP(1 0 0) surface generated metallic In about 60 nm in diameter.

Preparation of processed GaAs surface cleaning in view of molecular beam epitaxy regrowth by means of a O 2 SF 6 microwave plasma has been investigated. Photoemission, Auger electron spectroscopy, atomic force microscopy and secondary ion mass spectrometry have been used for characterization. The O 2 SF 6 plasma treatment was found to be very efficient for decontaminating the GaAs surface and leads to the formation of an oxide layer that can be taken off by a thermal or low-temperature H-plasma-assisted deoxidation. The levels of oxygen and carbon contaminants at the regrowth interface were measured to be in the range of a standard homoepitaxial layer–epiready substrate interface. Fluorine was observed to be eliminated upon deoxidation while sulphur is present, particularly in the case of low temperature grown layers. This plasma treatment was found to be efficient for preparation of processed GaAs surfaces for molecular beam epitaxial regrowth.

A multiple analysis of a defective nitrided case has been used to investigate different parts of the over layer region. Experiments by means of X-ray photoelectron spectroscopy (XPS), electron probe microanalysis (EPMA), light microscopy and microhardness measurements were done at different scales and information was given on the structural and physico-chemical properties. The metallographic study allowed estimating the nitrided case depth together with hardness and nitrogen concentration profiles in depth. Also, the irregular nitrogen concentration and the irregular hardness profiles, in a parallel direction to the surface, were correlated with the structure features in the nitrided sample cross-section. One can notice a reasonable connection among the different results, which gives a good understanding of the defective nitrided sample.

The nitridation of GaAs(1 0 0) surfaces has been studied using XPS spectroscopy, one of the best surface sensitive techniques. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. We used the Ga3d and As3d core levels to monitor the chemical state of the surface and the coverage of the species. A theoretical model based on stacked layers allows to determine the optimal temperature of nitridation. Moreover, this model permits the determination of the thickness of the GaN layer. Varying time of nitridation from 10 min to 1 h, it is possible to obtain GaN layers with a thickness between 0.5 nm and 3 nm.

This paper deals with the chemical and sensing properties of n-type indium phosphide (InP) epitaxial layers, which were applied in a novel resistive structure for gas detection. The influence of working temperature on the structure response to the oxidising gas, nitrogen dioxide (NO2), in the ppb range was investigated. Also, the in-depth profiles of charge carrier concentration and resistivity of the InP material were calculated at various temperatures. In order to understand better the sensing mechanism, a detailed analysis of the chemical properties of the InP surface before and after gas action was performed by means of X-ray photoelectron spectroscopy (XPS) combined with Auger spectroscopy (AES) and Ar+ sputtering of the sample.

Electron spectroscopy (AES and XPS) and photoluminescence analysis (PL) were used to study porous layers elaborated by electrochemical etching of p-GaAs and n-InP substrates. Surface characterizations have been performed on the as received porous substrates, ions bombarded and nitridated porous layers. Porous surfaces of GaAs(1 0 0) and InP(1 0 0) have been compared after different treatments: Argon ion bombardment and nitridation with a glow discharge source (GDS) in UHV. These processes have been followed by Auger measurements (AES). The effects of the bombardment and the nitridation of porous InP were studied. The PL investigations of the porous GaAs layer show visible and infrared photoluminescence bands. Quantum confinement in the nanocrystallites of GaAs formed by electrochemical etching can explain the luminescence of the porous GaAs layers.

This work attempts to characterize the Au/GaN/GaAs Schottky diode. The thin GaN film is realized by nitridation of GaAs substrates with different thicknesses (0.7–2.2 nm). We propose a study of the electrical quality of the components after the elaboration of the Au/GaN/GaAs systems; first without annealing and the second with annealing at 620 °C. Analysis of the current voltage I – V and capacitance voltage C – V characteristics of the Au/heated GaN/GaAs and Au/GaN/GaAs samples with 2.2 nm of GaN thickness allows the determination of the electrical parameter variations. Then, the ideality factor increases after the annealing at 620 °C and becomes equal to 2.86 and 2.77 for the 5 min and 30 min of nitridation, respectively. The calculated states density N ss shows less defects and traps in the Au/GaN/GaAs structure (not heated). It is seen that the electrical parameters of the Au/heated GaN/GaAs diode are significantly different from the conventional Au/GaAs Schottky diode. The improvement of the parameters may be attributed to the passivation of the GaAs surface with the formation of the GaN interfacial layer.

The effects of surface preparation and annealing on the electrical parameters of Au/InP and Au/InSb/InP Schottky diodes were investigated; in the latter diode, InSb forms a thin restructuration layer allowing the blockage of In atom migration to the surface. The current–voltage characteristics I – V G of these diodes were measured before and after restructuring. The electrical behavior of the components obtained after creation of Au/InP(100) interfaces before and after annealing of the substrate surface at 300 °C was examined. The analysis of the I – V G curves of Au/InP diodes shows a migration of chemical species towards the interface. The electrical characteristic of this contact is ohmic type when the InP surface is heated at 300 °C, and it is of Schottky type with a poor quality and with a height of the potential barrier equal to 0.44 eV when the InP surface is not heated. On the other hand, the Au/InSb/InP contact presents better electrical quality and structural properties when the InSb/InP surface is heated at 300 °C than when it is not. Thus, in the former case, the contact shows high value, about 0.63 eV, for the height of the potential barrier.

The effects of the energy density distribution and relaxation time of the interface state on electric parameters of Au/InSb/InP(100) Schottky diodes were investigated, in the latter diode, InSb forms a fine restructuration layer allowing to block P atoms migration to surface. To be sure of the disappearance of the In droplets, a high quantity of Sb was evaporated and the excess was eliminated by heating the substrate surface at 300 °C before evaporating Au onto it. The current–voltage I(VG) and capacitance–voltage C(VG) characteristics are measured as a function of frequency (100 Hz–1 MHz). Typical Ln[I/(1−e−qVG/kT)] versus VG characteristics of Au/heated InSb/InP(100) Schottky diode under forward bias show two linear regions separated by a transition segment. From the first region, the slope and the intercept of this plot on the current axis allow to determine the ideality factor n and the saturation current Is evaluated to 1.79 and 1.64×10−7 A, respectively. The mean density of interface states estimated from the C(VG) measurements was 1.57 1012 cm−2 eV−1. The interface states were responsible for the non-ideal behavior of the I(VG) characteristics, the capture cross-section σn for the fast slow varies between 2.16×10−11 and 7.13×10−12 cm2 for the relaxation times range 7.9×10−3–2.4×10−2s.

We report the Au catalyst-assisted synthesis of 20 μm long GaAs nanowires by the vapor-liquid-solid hydride vapor phase epitaxy (HVPE) exhibiting a polytypism-free zincblende phase for record radii lower than 15 nm down to 5 nm. HVPE makes use of GaCl gaseous growth precursors at high mass input of which fast dechlorination at the usual process temperature of 715 °C results in high planar growth rate (standard 30-40 μm/h). When it comes to the vapor-liquid-solid growth of nanowires, fast solidification at a rate higher than 100 μm/h is observed. Nanowire growth by HVPE only proceeds by introduction of precursors in the catalyst droplets from the vapor phase. This promotes almost pure axial growth leading to nanowires with a constant cylinder shape over unusual length. The question of the cubic zincblende structure observed in HVPE-grown GaAs nanowires regardless of their radius is at the heart of the paper. We demonstrate that the vapor-liquid-solid growth in our conditions takes place at high liquid chemical potential that originates from very high influxes of both As and Ga. This yields a Ga concentration systematically higher than 0.62 in the Au-Ga-As droplets. The high Ga concentration decreases the surface energy of the droplets, which disables nucleation at the triple phase line thus preventing the formation of wurtzite structure whatever the nanowire radius is.

EPES (elastic peak electron spectroscopy) allows measuring the percentage of elastic backscattered electrons η e from a surface excited by primary electrons. However, this method must be combined with Monte Carlo simulations to get quantitative information. After a brief description of the algorithm used in this work (named MC2), we focused on the adaptation of this simulation for nanoporous surfaces (named MC2-NP). The theoretical results obtained put in evidence the dependence of η e versus pore diameter (d), depth of the pores (h) and covering rate (CR) of the pores on the surface. Results obtained on surfaces having cylinder-shaped and cone-shaped holes with nanometer dimensions are presented too. To validate theoretical results obtained with MC2-NP, silicon(111) nanoporous surfaces have been prepared with an anodized aluminum oxide (AAO) template and by argon ion bombardment in an UHV chamber. Uniform nanohole arrays were formed as a replica of ordered lattice pattern of the template. Then EPES experimental measurements have been performed on planar and nanoporous Si(111) surfaces using a retarding field analyzer (RFA). The experimental results put in evidence that the percentage of the elastically backscattered electrons is influenced by the patterning of the surface. Then comparing values of η e obtained experimentally with those obtained with MC2-NP simulations, we show the sensitivity of the EPES method for studying nanoporous surfaces. In this way, we expect fast estimation of nanohole's dimensions by in-situ MM-EPES (Multi-Mode EPES) without other techniques such as for example scanning electron microscopy.

Indium phosphide (InP) is one of the most promising materials for applications in high speed and optoelectronic devices. Indium phosphide presents a high mobility and large band gap. However, the elaboration of InP components shows problems in the technology [L. Bideux, B. Gruzza, A. Porte, Surf. Interf. Anal. 20 (1993) 803–807; G. Hollinger, J. Appl. Phys. 67 (1990) 4173], because phosphorus is very volatile. Before the deposition of insulator and metal, InP surface is treated and well passive to get optimal conditions for the elaboration of electronic structure. We have shown that InSb buffer can reduce the phosphorus atoms migration and the defects at the interface [L. Bideux, C. Robert, B. Gruzza, V. Matolin, Z. Benamara, Surf. Sci. 352–354 (1996) 407–410]. After the elaboration of Au/InP, Au/InSb:InP, Al2O3/InP and Al2O3/InSb:InP structures, we have studied and characterized electrically these structures. The results obtained show clearly the reduction of the defects in the structures protected by InSb buffer layer and no treated surface compared with the InP ones.

The purpose of this paper is to characterize interface states in Au/InSb/InP(1 0 0) Schottky-type diodes and determine the effect of InSb surface preparation on the energy density distribution and relaxation time of the interface state. In the latter diode, InSb forms a fine restructuration layer allowing to block In atoms migration to surface. We have proceeded as follows: first, a great amount of antimony has been evaporated and, as a second step, the excess antimony is removed by heating the substrate at 300°C. The characteristic parameters of the interface states are derived from the capacitance-voltage C ( V G ), conductance–voltage G ( V G ) measured as a function of frequency and current–voltage I ( V G ) under forward biases. The mean density of interface states N ss estimated was 3.05×10 12 eV −1 cm −2 , the interface states were responsible for the non-ideal behavior of the I ( V G ) characteristics of the diodes. The relaxation times are independent of the bias and varies with N ss in the range 7.1×10 −4 s and 3.7×10 −3 s.

Photovoltages (surface photovoltage plus Dember voltage) were calculated, taking into consideration the influence of charge exchange between a continuum of surface states and the semiconductor, the barrier lowering as a result of the Schottky effect, the applied voltage drop and transmission coefficient across the interfacial layer. For moderate band bending, the photovoltage depends on several parameters which renders their reliable determination very difficult. For extreme band bending, however, only doping factor, mobility ratio and relative excess concentration enter into given formulas. The obtained analytical expression includes saturation effects at the surface, so that the photovoltage (SPV) does not exceed the thermodynamic band bending. The bulk effect of the Dember voltage is then added to obtain the relationship between the light generated current and open circuit voltage at the terminals. Results were applied to Schottky barrier diodes Au/InP(n). The InP substrate is restructured by some monolayers of InSb thin film [L. Bideux, B. Gruzza, A. Porte, H. Robert, Surface and Interface Analysis 20 (1993) 803]. Good agreement between parameters determined in this way and otherwise indicates the validity of the model and the approximations used in this work.

In this work, we measure the current–voltage ( I – V ) and the capacitance–voltage ( C – V ) characteristics of the Au/InP(100) and Au/InSb/InP(100) Schottky type diodes. The InP( n ) substrate is restructured by some monolayers of the InSb thin film. We then propose a study of the electrical quality of the elaborated components after the Au/InP interface creation; first without annealing and then after annealing by heating at 500°C temperatures. Analysis of the measured I ( V ) characteristics for the Au/InP and Au/InSb/InP samples allows the determination of the electrical parameter variations. The saturation current I s , the serial resistance R s , the mean ideality factor n and also the barrier height φ B n , are respectively equal to 2.10×10 −4 A, 19 Ω, 1.8 and 0.401 eV for the Au/InP sample and equal to 1.34×10 −7 A, 175 Ω, 1.78 and 0.592 eV for the Au/heated InSb/InP. Another good result is that the analysis and simulation of the I ( V ) and the C ( V ) characteristics allows us to determine the very important mean interfacial state density N ss(mean) , and is obtained to be equal 4.23×10 12 eV −1 cm −2 for the Au/InP sample and equal to 4.42×10 12 eV −1 cm −2 for the Au/heated InSb/InP. This work thus permits the evolution study of these electrical parameters related to the restructuration conditions.

Hydride vapor phase epitaxy (HVPE) is used nowadays for the growth of new III–V semiconductors (GaN, InGaN…), as well as for the selective epitaxy of III–V layers on patterned III–V [E.R. Messmer et al., Materials Science and Engineering B51 (1998), pp. 238–241] or silicon [O. Parillaud, E. Gil-Lafon, B. Gerard, P. Etienne, D. Pribat, Appl. Phys. Lett. 68 (1996), pp. 2654–2656] substrates. It has already been demonstrated that InAs/InP strained quantum wells [H. Banvillet, E. Gil-Lafon, R. Cadoret, P. Disseix, K. Ferdjani, A. Vasson, A.M. Vasson, A. Tabata, T. Benyattou, G. Guillot, J. Appl. Phys. 70 (3) 1991, pp. 1638–1641.] and InGaAs/InP quantum wells [N. Piffault, E. Gil, J. Leymarie, S.A. Clark, M. Anderson, R. Cadoret, A. Vasson, A.M. Vasson, J. Crystal Growth 135 (1994), pp. 11–22.] could be achieved by HVPE. We will present here the study of the growth of InAsP/InP strained quantum wells by HVPE. Relaxed InAsP layers were first grown in order to determine the composition of the alloys. Single quantum wells and multi-quantum well structures were then achieved. Photoluminescence analysis of the samples have shown the high quality of the InAsP/InP quantum wells. The feasibility of low dimensionality structures using HVPE process was then demonstrated, with an accurate control of the thickness and the composition of InAsP/InP quantum wells.

This work attempts to characterize the Au/InP Schottky diode at different temperatures (in the range 300–425 K). The InP surface is restructured with an InSb thin film with several monolayers. I(V) analysis versus different temperatures gives the saturation current variation Is (2×10−5–7×10−5 A), the mean ideality factor (1.7–1.24), the barrier height (0.47–0.45 V), and finally the serial resistance Rs variations (85–19 Ω). The doping concentration Nd and the diffusion voltage Vd are calculated using the C(V) characteristics. The concentration Nd is 3×1015 cm−3 at room temperature and increases with thermal activation to 7×1015 cm−3 at 425 K. Nevertheless, the diffusion voltage Vd is reversibly proportional to the doping concentration Nd and decreases from 33.7×10−2 to 29×10−2 V. The mean interfacial state density Nss decreases with increasing temperature, from 4.33×1012 to 1012 cm−2.eV−1. This improvement is the result of molecular restructuring and reordering at the Au/InP interface. For temperatures less than 375 K, the C(V) characteristic is controlled by an important interfacial state density and/or the presence of deep donor levels in the semiconductor bulk. At temperatures greater than 375 K, the C−2(V) curve is linear and the deep donor levels disappear. The traps effect is also reduced.

Alumina was evaporated on InP(100) and InSb/InP(100) substrates. The InSb buffer layer permits thermal and structural protection of the indium phosphide substrate. This layer was obtained by condensation of antimony atoms on the indium-rich InP surface after ionic etching. The evaporation of antimony leads to Sb-In bonds. Modellization of the Auger signal variations during alumina condensation was compared to the experimental results. Auger measurements indicate the improvement of the elaborated structure. This fact has been confirmed by the electrical C(V) characterizations.

In the fast electronic area, studies on InP metal—insulator—semiconductor (MIS) devices have wide interest. Effectively, InP presents a considerable interest due to its high mobility and large bandgap for high speed MIS devices. However, the InP surface must be treated and well passivated before the deposition of insulator. We show that the InSb buffer layer can reduce the phosphorus atom migration and the defects at the interface. After the elaboration of Al 2 O 3 /Si, Al 2 O 3 /InP and Al 2 O 3 :InSb/InP structures, we have studied and characterized electrically the alumina—semiconductor systems. Thus, a mercury probe was used as a temporary gate contact. In the Al 2 O 3 :InSb/InP structure, the electrical C–V characteristics plotted at 1 MHz give, in the depletion region, a more important slope of the curves. The obtained results show clearly the reduction of the defects, dangling bonds and consequently the state density has been decreased by 50% compared to the InP protected by an InSb buffer layer and no treated surfaces. Then, the interfacial state density N SS is evaluated as 4 × 10 11 eV −1 cm −2 .

In previous reports, we have investigated on the influence of current transport mechanism on the sensitivity of InP Schottky and pseudo-Schottky diodes, for nitrogen dioxide detection. In this paper, the influence of the metal nature and the structure of the rectifying contact on the sensing layer are highlighted. More especially, we will focus on the behavior of these Schottky structures during and after their exposures to nitrogen dioxide (NO2) and ozone (O3). In this context, two types of structures have been studied: the simple Schottky diodes and the more elaborated structures called pseudo-Schottky. These diodes are realized with Au or Pd as metals. First, we will describe samples preparation and electrical characterization of the two types of structures. Then, we will compare sensor responses of these different structures under NO2 and O3. Finally, to better understand the action of these gases on the sensitive layer (the Schottky contact), X-rays photoelectron spectroscopy (XPS) is performed to follow the evolution of the metallic layer. The poisoning effect of active sites, which appears after NO2 and O3 expositions, is illustrated by comparative study of the active layer before and after exposure.

International audience

We report the first synthesis of GaAs nanowires (NWs) by Au-assisted vapor-liquid-solid (VLS) growth in the novel hydride vapor phase epitaxy (HVPE) environment. Forty micrometer long rodlike monocrystalline GaAs nanowires exhibiting a cubic zinc blende structure were grown in 15 min with a mean density of 10(6) cm(-2). The synthesis of such long figures in such a short duration could be explained by the growth physics of near-equilibrium HVPE. VLS-HVPE is mainly based on solidification after direct and continuous feeding of the arsenious and GaCl growth precursors through the Au-Ga liquid catalyst. Fast solidification (170 microm/h) is then assisted by the high decomposition frequency of GaCl. This predominant feeding through the liquid-solid interface with no mass and kinetic hindrance favors axial rather than radial growth, leading to twin-free nanowires with a constant cylinder shape over unusual length. The achievement of GaAs NWs several tens of micrometers long showing a high surface to volume ratio may open the field of III-V wires, as already addressed with ultralong Si nanowires.

The model of quantitative interpretation of Auger electron spectroscopy (AES) results is described and some complementary electron energy loss spectroscopy (EELS) results are also reported. It is shown that the InP(100) surfaces perturbed by the Ar+ cleaning treatment can be ordered by Sb deposition. The variations of ditferent Auger lines are interpreted, and the transformations 3D → 2D of the initially formed In clusters can be well-followed during the frrst stages of the deposition. PACS numbers: 68.35.Βs, 68.35.Fx, 72.80.Ey, 82.80.Pv

International audience

Quantitative and qualitative analysis techniques were employed to study the first stages of ultra-high vacuum plasma nitriding of the 42CrMo4 steel. At constant treatment temperature, maintained for all samples at about 360 °C, we have established the influence of treatment time on the chemical composition, thickness and electrical properties of the nitrided layer. In this purpose it was used a stacking atomic layer model describing the sample surface, which takes into account the attenuation depth of photoelectrons by the atomic monolayers. So, we have found that after 2 h of nitriding in laboratory conditions, 70% of the nitrided layer was composed of iron oxide. Also, I – V measurements indicate an influence of the nitride overlayer with increasing treatment time.

International audience; The nitrides of group III metals: AlN, GaN and InN are very important materials due to their applications for short wavelength opto-electronics (light-emitting diodes and laser diodes). It is essential for the realization of such novel devices to grow high-quality nitride single crystals. In this paper, we report the first stages of the InP(1 0 0) surfaces nitridation in order to grow high-quality nitride films. Indeed, the nitridation process is an important step in the growth of nitrides [J. Vac. Sci. Technol. A 17 (1999) 2194; Phys. Status Solidi A 176 (1999) 595]. Previous works [Synth. Met. 90 (1997) 2233; Appl. Phys. Lett. 63 (1993) 1957] have shown that in situ Ar+ ions bombardment is useful on the one hand to clean the surface, and on the other hand to create droplets of metallic indium in well-controlled quantity. Then the indium metallic enrichment of the surface, monitoring by elastic peak electron spectroscopy (EPES) and Auger electron spectroscopy (AES) allows to prepare the III-V semiconductors surfaces to the nitridation step. The nitridated process has been performed with a high voltage plasma discharge cell and has been studied using quantitative Auger electron spectroscopy, elastic peak electron spectroscopy and electron energy loss spectroscopy (EELS), in order to optimize the conditions of InN layers formation.

Porous GaAs layers were formed by electrochemical etching of p-type GaAs(1 0 0) substrates in HF solution. A surface characterization has been performed on p-type GaAs samples using X-ray photoelectron spectroscopy (XPS) technique in order to get information about the chemical composition, particularly on the surface contamination. According to the XPS spectra, the oxide layer on as-received porous GaAs substrates contains As2O3, As2O5 and Ga2O3. Large amount of oxygen is present at the surface before the surface cleaning. Compared to untreated GaAs surface, room temperature photoluminescence (PL) investigations of the porous layers reveal the presence of two PL bands: a PL peak at ∼871 nm and a “visible” PL peak at ∼650–680 nm. Both peak wavelengths and intensities varied from sample to sample depending on the treatment that the samples have undergone. The short PL wavelength at 650–680 nm of the porous layers is attributed to quantum confinement effects in GaAs nano-crystallites. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-sized crystallites were observed on the porous GaAs surface. An estimation of the mean size of the GaAs nano-crystals obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results.

EPES (elastic peak electron spectroscopy) and AREPES (angle resolved elastic peak electron spectroscopy) are non destructive methods and very sensitive to the surface region. These techniques allow to measure the percentage η e of elastically backscattered electrons from the surface excited by an electron beam. Both methods are combined with Monte-Carlo (MC) simulations to interpret experimental results. In this work, we underline the importance of a micrometric scale roughness at the surface. The use of an original Monte-Carlo method was fruitful for the simulation, moreover 3D representations have been developed for visualization and qualitative interpretation of the results. For a more precise quantitative study, a 2D representation was necessary. The calculated results have been compared with published experimental ones got for different incidence angles and primary energies, on a silicon surface having triangular saw-tooth aspect (crenels) obtained by photolithography. We have observed that the effect due to the roughness increases with the incidence angle.

Quantitative X-ray photoelectron spectroscopy was used to characterize the native oxide film formed on 42CrMo4 steel surface by air exposure in normal conditions. In order to determine the thickness and composition of the oxide layer we have used a stacking layer model together with experimental XPS sputtering depth profiling. At a nanoscale study, to obtain quantitative results one must take into account fundamental parameters like the attenuation depth of photoelectrons. We have found that both lepidocrocit (γ-FeOOH) and magnetite (Fe3O4) were present and the total thickness of the oxide layer was 16 monolayers.

This article investigates the nitridation effect of InP(100) semiconductor surfaces performed using a glow discharge cell. Auger electron spectroscopy and XPS were used to understand the different steps of this process. An important point is the initial quantity of metallic indium on the InP(100) surfaces. Indeed the indium droplets, created in well-known quantity, play the role of precursor. At a relatively low temperature of 523 K the system undergoes surface restructuring, which includes removal of the In droplets and the formation of two InN monolayers. Phosphorus-nitrogen bonds have been detected by the analysis of P LMM Auger peaks, and In-N bonds by analysis of the In 4d XPS peak. However, the presence or not of metallic indium inside this InN overlayer is crucial for passivation of the substrate. Ex situ photoluminescence measurements correlated to the electron spectroscopies results have shown the good passivation effect of the InP(100) surfaces by InN overlayers for 40 min of nitridation.

International audience; Auger electron spectroscopy (AES) was used to investigate the processes taking place during the initial stages of InP(100) surfaces nitridation. This AES study combined with electrical measurements (intensity-potential) shows that the processes greatly differ depending on the nitridation angles. Results show that with grazing angle for nitrogen flow, the nitridation process is more efficient. Results obtained with AES spectra are coherent with electrical measurements : Hg/InN/InP(100) Schottky diodes present better electrical characteristics in the case of a grazing flow. That means, the adsorption of nitrogen on the surface is more important for this configuration.

The cleaning and the nitridation of GaAs(1 0 0) substrates have been studied in this work by electron energy loss spectroscopy (EELS), elastic peak electron spectroscopy (EPES) and X-ray photoelectron spectroscopy (XPS). The nitridation of GaAs(1 0 0) was performed using a double differential pumping RF cell. We have studied in a first part, the surface modifications of the substrate during ionic cleaning. In a second part, we have determined the λ i ( E ) K ( E , E n ) curves from EELS spectra using Tougaard's procedure for cleaned-GaAs(1 0 0) and nitrited-GaAs(1 0 0) substrates. The thickness of the GaN overlayer was deduced from these results.

A double chamber vacuum system was constructed for the electron spectroscopy study of GaN layer growth. The samples are prepared by vacuum deposition from Knudsen-type Ga source in the afterglow atmosphere of active nitrogen produced by high-pressure RF-plasma source. The growth chamber is connected to the analysis chamber equipped with electron spectroscopy (XPS, AES) analysis, permitting to study the chemical composition of layers as a function of growing conditions. It is shown that the new RF-source is suitable for preparation of pure stoichiometric GaN layers.