Defects in GaAs grown by molecular-beam epitaxy at low temperatures: Stoichiometry, doping, and deactivation of n-type conductivity

Positron annihilation experiments to study native defects in low temperature (LT) GaAs were conducted where doping and the stoichiometry were varied during the growth. Ga vacancies are identified in all samples by measuring the momentum distribution of core electrons surrounding the vacancy defect. The temperature dependence of positron annihilation parameters indicates that Ga vacancies are negative in Si-doped LT GaAs, but neutral in undoped and Be-doped material. It is proposed that the different charge states reflect different structures of complexes consisting of V_Ga and donor type defects.