OBSERVATION OF A VACANCY AT THE DX CENTER IN SI-DOPED AND SN-DOPED ALGAAS

A vacancy defect is observed by positron annihilation in n-type Si- and Sn-doped AlxGa1-xAs (x greater-than-or-equal-to 0.18). The vacancy is not observed after optical ionization of the DX center. The disappearance of the vacancy signal is persistent below a critical temperature. Thermal ionization of the DX center removes the vacancy signal above 300 K. We conclude that the deep ground state of the DX center contains the vacancy. The results are in perfect agreement with the theoretical predictions of the large displacements of the Si and Sn atoms from the substitutional configuration when the DX state is occupied.