Ga vacancies as compensating centers in homogeneously or δ-doped GaAs(Si) layers

The positron annihilation method was used to investigate the type and concentration of compensating centers in homogeneously or δ-doped GaAs(Si) layers grown by molecular beam epitaxy (MBE). The results show the presence of Ga vacancies and negative ions in both type of layers. The negative ion is attributed to the Si_As in homogeneously doped GaAs(Si) and to the Ga_As in δ-doped GaAs(Si). The concentrations of Ga vacancies and negative ions increase strongly when the Si concentration exceeds 5 × 10¹⁸ cm^-3 in homogeneously doped GaAs(Si) and 1 × 10¹³ cm^-2 in δ-doped GaAs(Si). Furthermore, the results in the superlattice indicate that the defects observed by the positron are located in undoped material between the delta planes.