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.
Epitaxial Growth of Semi-Insulating Gallium Arsenide
Semi-insulating gallium arsenide is grown epitaxially from the vapor phase by using chromyl chloride as a doping agent. The resistivity of the epitaxial layer is greater than 108 Ω·cm at room temperature. The temperature dependence of the resistivity gives an activation energy of 0.63 eV. Multilayer structure consisting of semi-insulating layer and n-type layer is obtained without halting growth process by flowing and stopping the chromyl chloride vapor. No dislocation is observed at the boundary between semi-insulating layer and n-type layer, though many dislocations are observed at the epitaxial-substrate interface. It is found that the grown layer becomes semi-insulating only when the donor concentration of the layer is lower than 5×1015 cm-3.