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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.

The energy loss function (ELF) is a key parameter for the calculations of energy losses undergone by electrons in matter. It is often the only input in the calculations performed within the models based on the semi-classical dielectric response theory. Its perfect knowledge is thus of primordial importance. To evaluate the ELF, it is usual to consider as a model an expansion in Drude-Lindhard (DL) type oscillators with fixed values of the strength, width, energy and dispersion for the various oscillators. However, for materials that are characterized by a single sharp oscillator as aluminium or indium, it has been shown [Phys. Rev. B 46 (1992) 2486] that the damping parameter that corresponds in the DL model to the width of the oscillator increases for decreasing incident electron energy. To emphasize this effect, we perform in this work systematic calculation of the ELF for an indium target and for incident electron energies between 200 and 2000-eV. The ELF is determined by comparing REELS (reflection electron energy loss spectroscopy) experimental inelastic electron scattering cross sections with cross sections calculated within the semi-classical dielectric response model, which is implemented in the QUEELS-e(k,ω)-REELS software (Quantitative analysis of Electron Energy Losses at Surfaces) [Surf. Interface Anal. 36 (2004) 824]. We also perform measurements and calculations for varying incident and exit angles of the electron, namely for angles to the surface normal between 15o and 75o, to check the validity of our results for all geometries. Our results show that the damping parameter of indium in the DL model for electron energy of 200-eV is three times larger than for energy of 2000-eV. Copyright © 2014 John Wiley & Sons, Ltd.

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.

International audience; X-ray photoelectron spectroscopy (XPS) was used to monitor the chemical changes resulting from irradiation (> 295 nm) in air of poly(3-hexylthiophene) (P3HT), polymer which is a good candidate for photovoltaic applications. The formation of carbonyl moieties and the stepwise oxidation of sulphur atoms were characterised. The oxidation and the cleavage of the hexyl side-chain was monitored. It is also shown that sulfur was first converted into sulfoxides, then into sulfones and finally into sulfinate esters. The formation of these ultimate degradation products provoked a disruption of π-conjugation in P3HT, leading to diminished visible absorbance. Based on these results, a mechanism of P3HT photooxidation is proposed. Comparison of XPS data with previously reported infrared and UV-visible spectral analysis showed that the information provided by these techniques is completely consistent.

The Multi-Mode Elastic Peak Electron Spectroscopy (MM-EPES) analysis is confined to incoherent electron elastic scattering and the use of variable primary energy. This experimental method is very sensitive to the surface region of the sample. However, for quantitative interpretation, the MM-EPES method needs jointly a Monte Carlo (MC) computer simulation of electron trajectories in the solid. In the present work, we proposed a new approach to calculate the percentage ηe of elastic reflected electrons by the surface of a sample. This simulation takes into account the surface effects (i.e. surface plasmon), and the atoms arrangement in the substrate. The concept of the surface excitation parameter (SEP) is also presented. Computer simulations were performed on the three low index single crystals of Cu, Au, Si and Ag. The results confirm that the distribution of substrate atoms, according to the crystallographic structure, influences the intensity measured by EPES. A simple prediction formula was proposed to calculate ηe for elastic electrons entering in a Retarding Field Analyzer (RFA) spectrometer which is the apparatus giving experimentally numerical values of the percentage ηe.

O2SF6 plasma effects on processed GaAs surfaces have been investigated. The influence of plasma parameters such as composition, power and exposure time has been studied. The microwave plasma treatment efficiency has been studied by surface depth profiling (cycles consisting of XPS measurements followed by a slight etching) coupled with an original modelling calculation. We have pointed out that SF6 addition in plasma increases the oxidative rule of oxygen by increasing the total oxide thickness and that the quantity of the different oxidative and passivating species does not limit the oxidative mechanism, in the O2:SF6 ratio range 80:20 to 40:60. The increase in the plasma power leads to a change in the composition of the outer region of the oxide layer with an increase in the gallium content on the surface, and to an increase in the total oxide layer. The exposure time to the plasma increases also these two phenomena.

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.

III–V semiconductor compound structures are widely applied in technology of advanced microelectronics, optoelectronics, and gas sensors. In this paper, we report on the use of XPS to characterize in situ the interaction of thermally activated hydrogen atoms and hydrogen molecules with InP(1 0 0) surfaces covered by thin InN overlayers. XPS spectra were taken with an ESCALAB-210 spectrometer after repeated hydrogenation cycles at temperatures up to 350 °C. The evolution of the In 3d, In 4d, P 2p, N 1s, O 1s and C 1s photoelectron spectra was carefully monitored. The XPS spectra of the hydrogen exposed surface revealed significant differences compared to those from the non-hydrogenated surface. InN films were found to be weakly reactive to hydrogen under experimental conditions explored. The behavior of P atoms at the hydrogenated surface was dependent on the parameters characterizing each hydrogenation (exposure, hydrogen species used, annealing temperature). Moreover, the heavily hydrogenated surface exhibited a phosphorus enrichment.

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.

Nitridation of GaAs(1 0 0) is performed using a double differential pumping RF cell. X-ray photoelectron spectroscopy (XPS) is used to monitor surface composition changes that result from ionic etching by Ar+ bombardment and nitridation of this substrate. We have studied the influence of temperature and pressure of nitrogen. The process of nitridation leads to the formation of a nitride layer which seems to be a ternary compound of gallium, arsenic and nitrogen. To improve the composition of the surface layer and to obtain pure GaN thin films on the surface by stopping arsenic migration, we have performed another kind of nitridation process. It consists, firstly, of a deposition of metallic gallium on the substrate surface. The system Ga/GaAs is then nitrided and the XPS measurements indicate the formation of a GaN layer on the surface.

Numerous data on the inelastic mean free path (IMFP) of electrons have been published, mainly for elemental solids and some inorganic and organic compounds. However, there is limited information available for IMFP values of binary alloy systems. Although IMFP values for different energies can be calculated for alloys from predictive formulae, IMFPs can be measured experimentally by elastic peak electron spectroscopy (EPES). In the present work, the IMFPs for three Au-Cu alloys-Au (25 at.%)-Cu (75 at.%), Au (50 at.%)-Cu (50 at.%), Au (75 at.%)-Cu (25 at.%)-were determined for the first time. The EPES experiments have been performed in three laboratories using spectrometers with different geometries and energy resolutions. The experiments were performed with the use of an Au standard (relative measurements) and without a standard material (absolute measurements). Two Monte Carlo algorithms were used to calculate the IMFPs. The IMFP energy dependence for the alloy samples has been obtained in the primary electron energy range 200-2000 eV. The measured IMFPs were compared with IMFPs calculated from two predictive formulae, i.e. the TPP-2M equation of Tanuma et al. and the G-1 equation of Gries. The scatter between the measured IMFPs and those calculated from the predictive formulae has been analysed statistically. The root-mean-square deviation from IMFP values calculated from the TPP-2M equation was 1.81-5.97 A, depending on the alloy surface composition and the particular EPES measurement, and it was smallest for the Au 25 Cu 75 alloy. The mean percentage deviation from the TPP-2M IMFPs was ∼27%.

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.

Intensity ratios of electrons backscattered elastically from thick, amorphous Si, polycrystalline Ag and Au, as well as various (vacuum evaporated, electrodeposited layers and metallic sheets) polycrystalline Ni samples, were measured using high energy resolution and two different experimental geometries (0° and 50° primary and 50° and 0° scattered beam angles relative to the surface normal, respectively) in the range of 1-5 keV primary electron beam energy. The elastic yield ratios obtained experimentally are compared to the results computed by Monte Carlo simulations using different algorithms and different sets of parameters. In the case of measured elastic yield ratios Si/Ni, Ag/Ni and Au/Ni, systematic differences were observed between the respective values obtained for two experimental geometries, whereas each Monte Carlo calculation predicted similar ratios for the different geometries. For the Si/Ag, Si/Au and Ag/Au elastic yield ratios, however, good agreement is observed between experiment and calculation, resulting in similar ratios for each geometry. As a conclusion to our study, we suggest that when using a polycrystalline Ni standard reference sample for measuring elastic yield ratios the homogeneity of the sample should be ensured. Our results confirm the applicability of elastic peak electron spectroscopy in the case of these solids for deriving IMFP values, i.e. no significant role of surface effects on the elastic yield ratios can be identified in the primary beam energy range studied.

Elastic peak electron spectroscopy (EPES) is based on measurements of elastic electron reflection coefficients. The angular distribution in EPES depends on different parameters such as atomic number of the substrate, the energy of the electron beam and the geometry of the analysis system. In this study, we compare the measured angular distribution of electrons elastically reflected from Pd and In surfaces with Monte-Carlo simulations. We have used a theoretical approach based on knowledge of electron trajectories and interaction effects inside the samples. For the experiments, we have constructed a special rotary energy analyser with a small aperture. The angular distributions of elastically backscattered electrons at 500 eV resulting from Monte-Carlo simulations of electron transport for Pd and In (atomic numbers 46 and 49) compare very well with the corresponding experimental measurements.

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.

The usefulness of elastic peak electron spectroscopy (EPES) has been demonstrated by application to a semiconductor study of indium phosphide or InAsP. In this paper, we present some results obtained with EPES. The inelastic mean free paths of indium phosphide have been calculated using EPES and the Monte-Carlo simulation or electron trajectories in solids. The second part of this work deals with the determination of the concentration of elements in heterostructures such as Au/InSb/InP(100) and InAs x P 1-x , and the results are compared to those obtained using AES.

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.

AES (Auger electron spectroscopy) and EELS (electron energy loss spectroscopy) have been used to study the first stages of the Al 2 O 3 Si and Al 2 O 3 InP interfaces formations. Alumina was condensed using an evaporation cell heated by an electronic bombardment. InP is one of the most promising materials for applications in high speed and optoelectronic devices, but surface and interface properties have an important influence on the performance of components. This paper is divided in two parts: (1) Test of alumina deposition on Si(100) substrates and comparison with published results. (2) Condensation on InP(100) substrates (cleaned with a Ar+ bombardment)

Efficient visible luminescence from porous Si (PSi) layers is associated with the quantum size and the presence of hydrogen as a passivant on the inner surface. The increase of the amount of H was performed by wet chemical etching in HF, producing the increase of photoluminescence intensity. The detection of H is not possible by AES or XPS and is difficult even with EELS. Elastic peak electron spectroscopy (EPES) showed a large decrease of the elastic reflection coefficient reappearing in the elastic peak, and measured with a retarding field analyser (RFA). The effective elastic backscattering coefficients of a monolayer of H, Si, O were calculated for the RFA angular window and resulted in reasonable agreement with literature data available

The mechanisms for the formation of the systems 〈Au/InP(100)〉 and 〈Au/InSb/InP(100)〉 are connected with their electrical properties. By using quantitative AES, a precise knowledge of the atomic mechanisms allows us to perform the desired component such as a Schottky diode. The best results are obtained for the 〈Au/heated InSb/InP〉 system with a barrier height of 0.7 eV.

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 nitridation of InP(1 0 0) surfaces has been studied using synchrotron radiation photoemission. The samples were chemically cleaned and then ion bombarded, which cleaned the surface and also induced the formation of metallic indium droplets. The nitridation with a Glow Discharge Cell (GDS) produced indium nitride by reaction with these indium clusters. We used the In 4d and P 2p core levels to monitor the chemical state of the surface and the coverage of the species present. We observed the creation of In-N and P-N bonds while the In-In metallic bonds decrease which confirm the reaction between indium clusters and nitrogen species. A theoretical model based on stacked layers allows us to assert that almost two monolayers of indium nitride are produced. The effect of annealing on the nitridated layers at 450 °C has also been analysed. It appears that this system is stable up to this temperature, well above the congruent evaporation temperature (370 °C) of clean InP(1 0 0): no increase of metallic indium bonds due to decomposition of the substrate is detected as shown in previous works [L. Bideux, Y. Ould-Metidji, B. Gruzza, V. Matolin, Surf. Interface Anal. 34 (2002) 712] studying the InP(1 0 0) surfaces.

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.

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.

In this study, InP(1 0 0) surfaces were bombarded by argon ions in ultra high vacuum. Indium metallic droplets were created in well controlled quantities and played the role of precursors for the nitridation process. A glow discharge cell was used to produce a continuous plasma with a majority of N atomic species. X-ray photoelectron spectroscopy (XPS) studies indicated that the nitrogen combined with indium surface atoms to create InN thin films (two monolayers) on an In rich-InP(1 0 0) surface. This process occurred at low temperature: 250 °C. Synchrotron radiation photoemission (SR-XPS) studies of the valence band spectra, LEED and EELS measurements show an evolution of surface species and the effect of a 450 °C annealing of the InN/InP structures. The results reveal that annealing allows the crystallization of the thin InN layers, while the LEED pattern shows a (4 × 1) reconstruction. As a consequence, InN related structures in EELS and valence bands spectra are different before and after the annealing. According to SR-XPS measurements, the Fermi level is found to be pinned at 1.6 eV above the valence band maximum (VBM).

The gas sensing, electrical and chemical properties of a novel toxic gas sensor structure based on n-InP epitaxial layers have been investigated. The gas sensing properties were investigated under extremely low concentration of toxic gas flow, nitrogen dioxide, in dry pure air. Responses, resistance changes ∃R, towards NO2 of the structures with different active InP layer thickness were compared. The influence of the surface states at InP surface on the initial resistance of the sensor structure was shown from numerical simulations. Furthermore, the changes of InP surface chemical properties due to gas exposition were stud-ied using the X-ray photoelectron spectroscopy (XPS).

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.

Ion beam nitridation of indium phosphide (100) substrates was studied using x-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES). Argon ion bombardment of the InP(100) surface removes the native oxides and induces the formation of three-dimensional indium clusters. After cleaning, the samples were nitrided in an ultrahigh vacuum chamber using a home-made radiofrequency plasma source (13.56 MHz) that allows nitridation at low pressures (10−4 Pa). We have studied the influence of temperature on the nitridation mechanisms. For low temperature (T < 200°C), no variation of the metallic indium droplets was observed; for high temperature (T > 270°C), the first layers of the substrate were damaged. The optimal temperature for the nitridation of InP(100) was found to be 250°C.