A. Bchetnia

GaN thermal decomposition in N2 AP-MOCVD environment

Undoped GaN layers were grown on SiN-treated (0 0 0 1) sapphire substrates by atmospheric pressure metal organic chemical vapor deposition (AP-MOCVD). The thermal decomposition of GaN layers was studied by in situ laser reflectometry and scanning electron microscopy (SEM) analysis. The thermal annealing process was performed in the MOCVD vertical reactor in the temperature range 900–1200 °C in N2 atmosphere. It was observed that annealing at temperature above 1100 °C causes the decomposition of GaN layers. An activation energy of 3.2 eV was deduced for the GaN thermal decomposition in N2 atmosphere. The GaN decomposed surface films were analyzed by SEM. These observations were correlated with the in situ laser reflectometry measurements.

Diffusion behaviour of vanadium in GaN thin films studied by secondary ion mass spectrometry

A sandwiched multi-structure made of alternatively undoped and vanadium (V) doped GaN layers was grown on SiN-treated (0 0 0 1) sapphire substrates by atmospheric pressure metal organic chemical vapour deposition (AP-MOCVD). The V diffusion in GaN has been investigated in the temperature range of 1000?1100 ?C by using secondary ion mass spectroscopy. The diffusion coefficients were obtained through a data-fitting program based on Ficks first law. The results suggest that V diffuses faster near the GaN/sapphire interface. During annealing, V redistributed by both in- and out-diffusion mechanisms. An activation energy of 2.9 ? 0.4 eV is estimated for V diffusion in GaN.

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.

Effects of thermal annealing on n-type GaAs:V grown by MOCVD

Vanadium (V)-doped GaAs (GaAs:V) layers grown by metal–organic chemical vapour deposition under different V-doping levels (1017–1019 cm−3) were annealed in an arsine–H2 gas mixture up to annealing temperatures of 750 and 850 °C for 30 min. The effect of thermal treatments on their electrical and optical properties was studied by means of the Hall effect, deep level transient spectroscopy and photoluminescence (PL). Annealing at 750 °C induces a thermal conversion from the n- to p-type of weakly V-doped GaAs. The conductivity of highly V-doped materials remains n-type. All the V-doped samples convert from n- to p-type following annealing at 850 °C. A comparison between the PL spectra for materials annealed under different conditions underlines the important role of gallium vacancies and a possible V accumulation at the surface in the case of thermal conversion.