OBSERVATION OF COMPENSATING GA VACANCIES IN HIGHLY SI-DOPED GAAS

Positron annihilation experiments have been performed to study the typ e and concentration of compensating defects in highly Si-doped GaAs gr own by molecular-beam epitaxy (MBE). The results show the presence of both Ga vacancies and negative ion defects, each of which act as accep ters in n-type GaAs. The concentrations of both types of defects incre ase strongly for Si concentrations exceeding 5x10(18) cm(-3). At [Si]g reater than or equal to 5x10(19) cm(-3), the concentrations of Ga vaca ncies and negative ions are comparable, and their sum represents a sub stantial fraction of the total concentration of Si itself. The results provide direct evidence that Ga vacancies play an important role in t he electrical deactivation of highly Si-doped MBE-grown GaAs.