NUCLEAR HYPERFINE INTERACTION OF THE DX CENTER AND ITS PERSISTENT PHOTOIONIZATION IN TE-DOPED AL(X)GA(1-X)AS

A well-defined spectrum component characterized by a large nuclear quadrupole interaction is observed in the Mossbauer spectra of Te-doped AlxGa1-xAs under conditions where the presence of DX centers is confirmed by electrical techniques. Upon illumination after cooling in the dark this component transforms partly into an unsplit Mossbauer line, reflecting photoionization of the DX center into a substitutional shallow donor. The lifetime of the photoionized centers is determined from the time evolution of the Mossbauer spectra. The hyperfine interaction parameters derived from the Mossbauer spectra are consistent with a large lattice relaxation and a pure p-electron imbalance at the DX center.