Almost stoichiometric epilayers, which were doped with Si or Be, were grown by means of molecular beam epitaxy at low temperatures. Excess As point defects in the epilayers, which acted as trapping sites for free carriers, were studied by means of Hall effect measurements. Under given As/Ga flux conditions, the concentrations of excess As point defects which trapped free carriers increased with increasing Si or Be concentration. For a given dopant concentration, the concentrations of excess As point defects increased linearly with the As/Ga flux ratio. The dependence of carrier mobility upon the trapped carrier concentration indicated that free carriers were trapped by neutral point defects and changed them into ionized ones. In epilayers which were very close to the stoichiometric composition, Si exhibited an amphoteric nature and occupied both donor and acceptor sites; resulting in self-compensation.

Electrical Properties of Nearly Stoichiometric GaAs Grown by Molecular Beam Epitaxy at Low Temperatures. S.Fukushima, T.Obata, N.Otsuka: Journal of Applied Physics, 2001, 89[1], 380-5