GaAs(001) substrates nitrided with N-2 plasma at various temperatures were investigated after being exposed to air for 40 days. They were studied by means of parallel angle-resolved X-ray photoelectron spectroscopy, scanning electron microscopy, micro-photoluminescence and time-resolved photoluminescence (TRPL). Several nitrided GaAs Schottky diodes were manufactured to find the optimal nitridation conditions for high diode quality. An improvement on the ideality factor was achieved for a diode with 1.3 nm-thick GaN layer grown at room temperature and crystallized at 620 degrees C. The crystallization process was needed to enhance the air-exposed GaAs photoluminescence efficiency by a factor 15. TRPL measurements showed a spectacular increase in the decay time (x4), even for a sample exposed to air for 2 years. A high level of GaAs surface chemical protection was achieved. Indeed, neither the element arsenic As-0 nor Ga and As oxides states were detected at the GaN/GaAs interface for nitridation at high temperature (500 degrees C), yielding a 3.1 nm-thick GaN layer. However, for nitridation temperatures above 300 degrees C, pits with an inversed pyramidal shape and square base were formed at the surface, their size increased as nitridation temperature was raised. These pits acted as non-recombination centers which reduced the GaAs photoluminescence yield.

Two kinds of N-2 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 degrees 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 Delta E-v 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 Delta E-c 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.

A non-destructive new imaging technique called Multi-Mode Elastic Peak Electron Microscopy (MM-EPEM), hypersensitive to surface chemistry and with an in-depth resolution of one atomic monolayer was developed. This method consists on performing several MM-EPEM images containing n × n pixels associated to an intensity of the elastic backscattered electrons by varying the incident electron energy in the range 200-2000 eV. This approach allows obtaining depth sampling information of the analyzed structures. Furthermore, MM-EPEM is associated with Monte-Carlo simulations describing the electron pathway in materials in order to obtain very precise quantitative information, for instance the growth mode and the organization of ultra-thin layers (2D materials) or nanoparticules. In this work, we used this new method to study the deposition of very small amount of gold down to one monolayer. Example of 3D reconstruction is also provided.

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.

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 effects of surface preparation and illumination on electric parameters of Au/GaN/GaAs Schottky diode were investigated. The thin GaN film is realized by nitridation of GaAs substrates with different thicknesses of GaN layers (0.7 - 2.2 nm). In order to study the electrical characteristics under illumination, we use an He-Ne laser of 632 nm wavelength. The I(V) current-voltage, the surface photovltage SPV measurement were plotted and analysed taking into consideration the influence of charge exchange between a continuum of the surface states and the semiconductor. The barrier height Phi(Bn), the serial resistance R-s and the ideality factor n are respectively equal to 0.66 eV, 1980 Omega, 2.75 under dark and to 0.65 eV, 1160 Omega, 2.74 under illumination for simple 1 (GaN theckness of 0.7 nm). The interface states density N-ss in the gap and the excess of concentration delta(n) are determined by fitting the experimental curves of the surface photovltage SPV with the theoretical ones and are equal to 4.5 x 10(12) eV(-1) cm(-2), 5 x 10(7) cm(-3), respectively, for sample 1 and 3.5 x 10(12) eV(-1) cm(-2), 7 x 10(8) cm(-3) for sample 2 (GaN theckness of 2 nm). The results confirm that the surface photovoltage is an efficient method for optical and electrical characterizations.

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. (C) 2015 Elsevier B.V. All rights reserved.

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 degrees 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 degrees 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. (C) 2015 Elsevier Ltd. All rights reserved.

This article reports the study of Au/GaN/GaAs Schottky diodes, where the thin GaN film is prepared by nitridation of GaAs substrates with thicknesses of 0.7 and 0.8 nm. The resulting GaN sample with thickness 0.8 nm is then treated with an annealing operation (heating to 620 degrees C) to improve the current transport. The current-voltage (I-V) and capacitance-voltage (C-V) of the Au/GaN/GaAs structures were investigated at room temperature. In fact, the I-V characteristics show that the annealed sample has low series resistance (R-s) and ideality factor (n) (63 Omega, 2.27 respectively) when compared to the values obtained in the untreated sample (1.83 k Omega, 3.31 respectively). The formation of the GaN layer on the gallium arsenide surface is investigated through calculation of the interface state density N-SS with and without the presence of series resistance R-s. The value of the interface state density N-SS(E) close to the mid-gap was estimated to be in the order of 4.7 x 10(12) cm(-2) eV(-1) and 1.02 x 10(13) cm(-2) eV(-1) with and without the annealing operation, respectively. However, nitridation with the annealing operation at 620 degrees C improves the electrical properties of the resultant Schottky diode.

In this paper, electrical characterisation and analytical modelling of current-voltage ( I - V ) and capacitance-voltage ( C - V ) for Hg/InN/n-InP Schottky structures are investigated. We have studied electrically thin InN films realised by the nitridation of InP(100) substrates using a glow discharge source (GDS) in ultra high vacuum. So, we have calculated, using I - V and C - V measurements, the ideality factor n , the saturation current I s , the barrier height

The current-voltage (I-V) characteristics of Pt/(n.u.d)-GaN and Pt/Si-doped-GaN diodes Schottky are investigated. Based on these measurements, physical mechanisms responsible for electrical conduction have been suggested. The contribution of thermionic-emission current and various other current transport mechanisms were assumed when evaluating the Schottky barrier height. Thus the generation-recombination, tunneling and leakage currents caused by inhomogeneities and defects at metal-semiconductor interface were taken into account.

•Determination of correction function of a hemispherical analyzer (HSA).•Visualization of analysis area using elastic backscattered electron images.•Dependence of analysis area and transmission function with the kinetic energy.•Efficiency of these functions for quantitative interpretations of XPS.•Description of the general methodology to use these functions.

In this work, electrical characterization of the current-voltage and capacitance-voltage curves for the Metal/InN/InP Schottky structures are investigated. We have studied electrically thin InN films realized by the nitridation of InP (100) substrates using a Glow Discharge Source (GDS) in ultra high vacuum. The I (V) curves have exhibited anomalous two-step (kink) forward bias behaviour; a suitable fit was only obtained by using a model of two discrete diodes in parallel. Thus, we have calculated, using I(V) and C(V) curves of Hg/InN/InP Schottky structures, the ideality factor n, the saturation current Is, the barrier height φ B , the series resistance Rs, the doping concentration Nd and the diffusion voltage Vd. We have also presented the band diagram of this heterojunction which indicates the presence of a channel formed by holes at the interface InN/InP which explain by the presence of two-dimensional electron gas (2-DEG) and this was noticed in the presentation of characteristics C(V). Copyright © 2014 IFSA.

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‐ε(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.

Current-voltage and capacitance-voltage characteristics of Au/n-GaNSchottky diode have been measured over the temperature range from 80 to 300 K. I(V) analysis versus different temperatures gives the saturation current variation Is (2.96x10(-29) A - 1.91x10(-11) A), the mean ideality factor (1.85 - 1.18), the barrier height (0.48 V - 0.86 V), and finally the serial resistance R-s variations (1050 5) - 65 Omega). The doping concentration N-d and the diffusion voltage V-d are calculated using the C(V) characteristics. The concentration N-d is evaluated to 4.14x10(16) cm(-3) at 125 K and increases with the thermal activation to 8.32x10(16) cm(-3) at 300 K. Nevertheless, the diffusion voltage V-d is reversibly proportional to the doping concentration Nd and decreases from 0.75 V to 0.56 V. The mean interfacial state density N(ss)decreases with the temperature increasing, from 4.6x10(12) cm(-2) eV(-1) to 1.9x10(12) cm(-2).eV(-1). This improvement is the result of the molecular restructuring and the reordering at the Au/GaN interface.

Gallium nitride is the most promising III-V semiconductor, in many applications. Due to its large direct band gap (3.4 eV), GaN can be dedicated as well to optoelectronics devices, e.g. blue lasers and photo-detectors as to the realisation of transistors operating in high-frequency and high-temperature regimes. Therefore, the technology of GaN films on standard substrates, GaAs, attracts special attention. In this paper, nitridation process of GaAs (100) substrates was studied in-situ using x-ray photoelectron spectroscopy (XPS) and ex-situ by means of electrical methods (I-V and C-V) in order to determine chemical, electrical and electronic properties of the elaborated GaN/GaAs interfaces. At first, native oxides were removed from the n-GaAs (100) surface by an argon ion bombardment. Next, a thin film of GaN was obtained by means of the nitridation on the GaAs substrate in an ultrahigh vacuum system using a radio-frequency plasma source (13.56 MHz), which allows nitridation at low pressures (10(-4) Pa). The Schottky diode (Hg on the fabricated GaN/GaAs structures) was characterised by I-V and C-V analysis. The saturation current Is, the mean ideality factor n, the barrier height Phi(BN), and the serial resistance R-s are determined from the I-V measurements. The C-V curves were controlled by the interfacial state density N-ss(E) and by the deep donor levels in the semiconductor bulk. Correlation among chemical, electronic and electrical properties of the GaN/GaAs interface was discussed.

Auger electron spectroscopy (AES) was used to understand the different steps of the indium phosphide nitridation and the annealing of the InN films. The AES analysis combined with electrical characterisation using the current-voltage I(V). After ionic cleaning with Ar+ ions, metallic indium crystallites are created and the nitridation of the InP substrates is performed using a plasma Glow discharge source (GDS). We used the In-MNN, N-KLL and P-LMM Auger transitions to monitor the chemical state of the surface. We observed that after nitridation, the creation of InN and P-N bonds while the In-In metallic bonds decrease. This confirms the reaction between indium clusters and nitrogen species. After these operations, we observed the effect of annealing on the nitridated layers at 450 degrees C during 15 min. It appears after heating that the In-N bonds decreases and the P-N bonds increases. A theoretical model based on stacked layers allows us to confirm that two monolayers of indium nitride are created on InP (100) surface. After this operation we note a presence of an important quantity of metallic indium at the surface using Auger analysis. In fact, the (I-V) characteristics reveal a low series resistance (168 Omega) for the annealed sample compared with a value of 1687 Omega obtained in the not annealed ones. We believe it's caused by the destruction of the nitride layer. The results obtained, with AES spectra are coherent with electrical measurements; they suggest that the InN films are significantly affected by the temperature.

The III-V semiconductors materials and in particularly Indium Phosphide are a promising candidates for the elaboration of high speed electronic compounds. The importance of the interface study is increasing considerably in the last years to understand, the mechanism of interface formations and to control perfectly the technology of the elaborated compounds.This study presents an electrical characterization of InP(p)/InSb/Al2O3/ Au structures in the range of temperature varying from the temperature of liquid nitrogen to the temperature of 400 degrees K. In order to give the evolution of electrical parameters of these structures with temperature, we have realized Capacitance-Voltage measurements at high frequency for different temperatures. The found results show that there is dispersion in the accumulation region as function with temperature. The quantity of positive charges in the insulator is estimated to 1.37x10(12) atm/cm(2) at room temperature. This value decreases slightly with increasing temperature. It varies from 1.57x10(12) atm/cm(2) at 77 degrees K to 1.12x10(12) atm/cm(2) at 400 degrees K. The interface insulator/semiconductor of our samples presents a good electronical quality, the state density is equal to 4.10(11) eV(-1).cm(-2) at room temperature, this one increases from 4.7x10(10) eV(-1).cm(-2) to 7.10(11) eV(-1).cm(-2) when temperature increases from 77 degrees K to 400 degrees K.