L. Bideux

Modelization and characterization of Au/InSb/InP Schottky systems as a function of temperature

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.

Record Pure Zincblende Phase in GaAs Nanowires down to 5 nm in Radius

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.

Fast growth synthesis of GaAs nanowires with exceptional length.

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 <111> 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.

Analysis and simulation of Au/InSb/InP diode C–V characteristic: modeling and experiments

Abstract 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.

Electrical parameters evolution of Au/InP(100) and Au/InSb/InP(100) systems with restructuring conditions

Abstract 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.

Electrons elastically backscattered from Al, Ag and Au samples

The objective of this study is to exhibit the capability of Monte-Carlo simulation in the frame of surface spectroscopy using elastically reflected electrons. Our computer programme is based on sample descriptions as stackings of atomic layers. Results allow us information on important parameters as the penetration depth of the electron beam or angular reflections. The programme has the capability for performing 3 D mapping of the backscattered electrons. Measurements of the percentage of the reflected current are depending on the geometry of the analysis system. This can be shown by the relief of the three dimensional patterns.

A Monte Carlo study for electron elastic backscattering based on layered models for substrates

The Monte Carlo programme used for the simulation of electron transport is based on a description of the samples by a layered model. The simulation accounts for the elastic scattering of electrons in selected materials and provides results to process the experimental data. In this paper, we present a detailed calculation method for determining the probabilities of elastic scattering by atoms, depending on the energy of the electrons. Reported results indicate that the accuracy of surface analysis can be improved by application of the developed Monte Carlo algorithm.

Elastic reflection of electrons by porous silicon layered (PSL) surfaces: effects of porosity

The electrical and optical properties of porous silicon layers deposited on silicon substrates are determined by their electrochemical preparation conditions. Porous silicon layers (PSL) deposited on low resistivity (10−3 ω cm) boron doped p+ Si exhibits channel structure, whereas layers formed on p type (1–3 ω cm) Si wafers are sponge type. In the abundant literature on PSL, little attention was paid to their electron spectra. We presented in this paper, a study of p+ and p type PSL samples by elastic peak electron spectroscopy (EPES). The elastic reflection coefficient re(E, P) is strongly affected by physical parameters of the sample as the porosity, the substrate Si type as well the presence of H adatoms within the pores. re(E, P) spectra are measured in absolute units (%) with a retarding field analyzer. A general tendency of spectra was the decrease of intensity with P (porosity) and E (primary electron energy). We have observed that HF treatment of the samples is producing a dramatic decrease of reH(E, P) in the low energy range (E = 50–150 eV). reH(E, P) intensities were measured at E = 50, 100 and 150 eV. We observed that the excess reflection (coming from the pores sides) becomes important for porosity P > 0.6. A phenomenological model is presented based on the intact Si surface and reflection of electrons from the pores.

Some problems of electron spectroscopy (AES, EPES) using a retarding field analyser

Abstract The retarding field analyser (RFA) proved to be advantageous in electron spectroscopy due to its high luminosity and by providing LEED simultaneously with AES and EPES. RFA is very efficient for determining the inelastic mean free path of electrons by EPES. Dolinski et al measured the elastic peak by repelling the electron beam using a bias potential on the sample. In this paper a further development of this procedure is described supplying the true percentage of elastically scattered electrons collected by RFA. The percentage has been determined by our RFA with optimized bias potential of the sample for primary energies between 100 and 2000 eV. It was deduced from the high energy side of the elastic peak because the background affects the detected signal on the low energy side. The experimental curve of elastic reflection coefficient is presented for indium. The measured elastic peak is distorted by the analyser. The spectrometer response of an RFA was determined by analysing the peak shape of deflected electrons after optimization of the bias voltage of the sample. The peak shape shows asymmetry since the low energy side differs from the Gaussian like high energy side. The distortion produced by RFA is similar to that observed by Taylor. It is enhanced by the background adjacent to the elastic peak. A computer algorithm was elaborated for reconstruction of the elastic and Auger peaks. Corrected curve is presented for indium Auger peak.

Retarding field analyser used in elastic peak electron spectroscopy

Abstract The percentage, η e ′ of electrons elastically reflected by a substrate is a fundamental parameter for elastic peak electron spectroscopy (EPES). A Retarding Field Analyser with its large acceptance angle can be used for this spectroscopy. However, distortion is observed in the low energy side of the recorded elastic peak, increasing with the energy of the impinging electrons, which introduces difficulty for η e measurement. To eliminate this difficulty, we propose in this paper a method to obtain η e using a reference curve. The process is applied to the study of the Ag Mo system, as well as experimental determination of the mean free path of electrons in indium samples.