Incorporation and thermal stability of defects in highly p-conductive non-stoichiometric GaAs:Be

Non-stoichiometric GaAs is known to contain a high concentration of native point defects. The dominant defect in the epilayers is the arsenic antisite (As-Ga), a deep double donor, which is incorporated at low growth temperatures (commonly between 200degreesC and 300degreesC) in molecular beam epitaxy (MBE). Consequently, p-doping of non-stoichiometric GaAs is difficult because large concentrations of acceptors are compensated by the As-Ga. Recently, we found that despite this compensation effect we can achieve p-conductive GaAs: Be with almost one order of magnitude higher Be-doping than previously obtained in MBE grown GaAs. The kinetics of dopant incorporation during MBE growth at these low growth temperatures seem to allow pushing the doping concentration further beyond thermal equilibrium. The epilayers, which are about 1 mum thick, are pseudomorphic with a lattice mismatch to the substrate of up to Deltac/c = -0.4%. They remain free of structural defects such as dislocations and stacking faults. After annealing at 600degreesC only the highest doped epilayers show a reduction in the Be concentration although the layers remain ultrahigh p-conductive. The increased incorporation of Be as well as its unusual stability in non-stoichiometric GaAs is likely influenced by the native defects in these layers, double positively charged As-Ga defects and probably neutral gallium vacancies (V-Ga). This novel material which is solely achievable through low-temperature growth may significantly enhance III-V semiconductor applicability due to ultrahigh doping capability with increased thermal stability. (C) 2001 Elsevier Science B.V. All rights reserved.