Observation of compensating Ga vacancies in highly Si-doped GaAs

Positron annihilation experiments have been performed to study the type and concentration of compensating defects in highly Si-doped GaAs grown by molecular-beam epitaxy (MBE). The results show the presence of both Ga vacancies and negative ion defects, each of which act as acceptors in n-type GaAs. The concentrations of both types of defects increase strongly for Si concentrations exceeding 5 ×{} 10¹⁸ cm^-3. At [Si] {≥}5 ×{} 10¹⁹ cm^-3, the concentrations of Ga vacancies and negative ions are comparable, and their sum represents a substantial fraction of the total concentration of Si itself. The results provide direct evidence that Ga vacancies play an important role in the electrical deactivation of highly Si-doped MBE-grown GaAs.