Positron annihilation experiments were performed in order to study the type and concentration of compensating defects which existed in highly Si-doped material that had been grown by means of molecular beam epitaxy. The results revealed the presence of both Ga vacancies and negative ion defects, each of which acted as acceptors in n-type samples. The concentrations of both types of defect increased markedly for Si concentrations that exceeded 5 x 1018/cm3. At Si concentrations that were greater than 5 x 1019/cm3, the concentrations of Ga vacancies and negative ions were comparable, and their sum represented a substantial fraction of the total concentration of Si. The results provided direct evidence that Ga vacancies played an important role in the electrical deactivation of highly Si-doped molecular beam epitaxially grown GaAs.

T.Laine, K.Saarinen, J.Mäkinen, P.Hautojärvi, C.Corbel, L.N.Pfeiffer, P.H.Citrin: Physical Review B, 1996, 54[16], R11050-3