A. Rebey

Photoreflectance and photoluminescence study of annealing effects on GaAsBi layers grown by metalorganic vapor phase epitaxy

The optical properties of GaAsBi layers grown by atmospheric pressure metalorganic vapor phase epitaxy on p-type GaAs substrates and annealed at different temperatures are investigated by photoreflectance and photoluminescence spectroscopies. Photoreflectance spectra show no significant shift in the band gap energy of GaAs0.965Bi0.035 with annealing temperature except 600 °C for which the band gap energy reaches a minimum value corresponding to a red shift of 60 meV. The low temperature photoluminescence spectra of GaAsBi layers show a broad band centered at ~1.36 eV. The temperature dependence of the 1.36 eV emission band in addition to the increasing intensity of this band with bismuth flow suggests that it is originated from Bi clusters or from complex defects probably located at the surface/interface of the GaAsBi epilayer.

Effect of thermal annealing on structural and optical properties of the GaAs0.963Bi0.037 alloy

We have investigated the effect of thermal annealing on GaAs0.963Bi0.037 layers grown by atmospheric pressure metalorganic vapour phase epitaxy. High resolution x-ray diffraction (HRXRD) patterns show high crystalline quality and remarkable stability against thermal annealing up to 700 °C. When the annealing temperature reaches 750 °C, the GaAs0.963Bi0.037 alloy is no longer stable, and the HRXRD pattern reveals the presence of other peaks. Atomic force microscopy images show a surface accumulation of Bi islands which disappear at 750 °C. The photoluminescence (PL) is clearly improved after annealing, but no shift of the PL peak was observed. The optimal annealing temperature is found to be ~700 °C.

Annealing Effect on GaN Buffer Layer Surface

We investigate the effect of annealing parameters (carrier gas, duration) on GaN buffer layers grown by metalorganic vapor phase epitaxy. The samples were characterized in situ by a laser reflectometry (LR) set-up with a He–Ne laser beam and ex situ by atomic force microscopy (AFM). The reflectivity decreases when the temperature is about 1050 °C. This fact depends on the hydrogen flow rate in the H2 + N2 gas mixture and the thickness of the buffer layers. The correlation between this observation and the AFM images indicates that H2 generates a mass transport on the substrate surface and a three-dimensional (3D) mode surface morphology for thick buffer layers. For thin buffer layers this phenomenon is limited and the sample surfaces have a two-dimensional aspect (2D) similar to that obtained under N2 rich annealing ambient. Under this ambient, no surface transformation is observed for longer annealing duration, which means that all the surface transformations occur during the temperature ramp between 600 and 1050 °C.

Study of GaAs layers grown on Ge substrates by MOVPE and in situ monitored by laser reflectometry

Metalorganic vapor phase epitaxy (MOVPE) of GaAs on Ge substrate has been studied by laser reflectometry (LR) with 632.8 nm laser beam. The layers were grown by varying substrate temperature and the V/III ratio. The relative difference between refractive index of film and substrate results in pronounced easily detected interference oscillations in the reflected beam intensity. The oscillations period provides an accurate and immediate measure of growth rate. In addition, the variations of extrema of oscillations and the average value of reflectance provide an estimate of the quality and surface roughness. A procedure for quantifying the roughening observed during the in situ LR monitoring of growth was presented. Furthermore, the measured interference effects were analyzed by calculating the reflectance. In order to explain the reflectometry behavior, the film was also characterized by X-ray diffraction and scanning electronic microscopy.

Growth of GaN Films on Porous Silicon by MOVPE

In this work, we report on the growth of GaN films on Porous Silicon (PS) substrates by the Metalorganic Vapour Phase Epitaxy (MOVPE) technique. The growth of GaN has been controlled by in-situ laser reflectometry. The growth rate was found to depend on growth temperature. X-ray Diffraction (XRD) patterns show that the epitaxial films correspond to that of GaN. The morphology and density of the nano-scale GaN layers were determined by atomic force microscopy (AFM) measurements. These first results show that PS is a promising candidate for obtaining GaN films.

Hot filament assisted metalorganic vapor-phase deposition of GaN

Hot tungsten filament is investigated as an ammonia precracking technique for the low temperature of MOVPE GaN. Samples were grown using different filament temperatures (Tf) and under different (N2, H2) carrier gas compositions. Results were discussed to take ones stand on a thermodynamic analysis of NH3 decomposition as a function of temperature. It appears that the growth kinetics is controlled by the ammonia adsorption for low filament temperatures ( 1800 K results in low growth rate. This was related to NH2 decomposition into atomic nitrogen (N) and hydrogen (H). The recombination of atomic nitrogen before reaching the substrate seems to be significant enough so as to limit the deposition rate. Secondary ion mass spectrometry analysis revealed a decrease in the hydrogen contamination as Tf increases.

Spectroscopic ellipsometry study of GaAs1−xBix material grown on GaAs substrate by atmospheric pressure metal-organic vapor-phase epitaxy

The optical properties in terms of complex dielectric function of GaAs1−xBix alloys (0%≤x≤3.7%), grown by atmospheric pressure metal-organic vapor-phase epitaxy, are determined by using room temperature spectroscopic ellipsometry. The interband transition energies in the energy range of 1.4–5.4 eV are resolved using a line shape fitting on the numerically calculated dielectric function second derivatives. The bismuth effect on the critical point parameters is then determined. We have found that, as for GaAs1−xBix alloys E0 transition, the bismuth incorporation shifts the E1, E1+Δ1, E2, and E0′ transition energies but with a lower magnitude. We also observed a root-square-like increase of the E1 broadening parameter (Γ1) with respect to the bismuth composition.

Carriers confinement study of GaNAsBi/GaAs QWs emitting at 1.3 and 1.55 μm

Band structures of GaN0.58yAs1–1.58yBiy/GaAs quantum wells (QWs) were studied using the band anticrossing model and the envelope function approximation. The confined states energies and the oscillator strengths of interband transitions were determined for well widths LW and Bi composition y varying in the range of 4–10 nm and 0–0.07 respectively. The emissions 1.3 and 1.55 μm were reached for specific couples (LW, y). The band anticrossing effect on the in-plane carriers effective mass has been investigated at k = 0. The absorbance spectra were calculated for QWs operating at 1.3 and 1.55 μm.

Characterization of GaN layers grown on porous silicon

Abstract This work reports the first successful results of the growth of GaN on a porous silicon (PS) substrate. GaN layers have been grown on PS substrates by metalorganic vapour phase epitaxy (MOVPE) at atmospheric pressure. The growth rate (measured by laser reflectometry) was found to be dependent on the growth temperature. The surface morphology and crystallinity of the GaN films were characterized by atomic force microscopy (AFM), and X-ray diffraction (XRD). I – V and C – V characteristics of the GaN/PS structure measured at room temperature are reported. We found that the GaN/PS/Si heterojunction forms a diode-like structure with a rather good rectification behaviour.

New photoluminescence lines in Vanadium doped GaAs grown by MOVPE

We examined the electrical and optical properties of vanadium-doped GaAs grown by metalorganic vapour phase epitaxy using vanadium tetrachloride (VCl4) as a novel dopant source. Samples with various vanadium incorporations were investigated. All samples were n type. The electron concentration dependence on the VCl4 flow rate was established. At 15 K, by comparison with undoped layers grown in the same conditions, photoluminescence spectra of V-doped exhibited three new emission bands: at 1.41, 1 and 0.72 eV. The 1 and 0.72 eV band emissions were attributed to V 2þ and V 3þ intracenter emission, while the 1.41 eV band was suggested to be a donor-bound transition. The identity of the donor is tentatively attributed to a donor complex that associates vanadium to an arsenic vacancy. From Hall effect as function of temperature, the donor ionisation energy was estimated to be about 102 ^ 5 meV. q 2003 Elsevier Science Ltd. All rights reserved.