Deep-level transient spectroscopy, and single-shot capacitance techniques, were used to investigate Si-doped samples of AlxGa1-xAs, where x ranged from 0.30 to 0.59. Under illumination, an additional deep-level transient spectroscopic peak was observed in samples with x-values that were close to 0.38. This peak was shown to originate from a localized state with an energy level that was shallower than the DX ground state, and from energy barriers to both electron emission and capture processes. Persistent photoconductivity effects that were related to this state were observed at temperatures below 50K. The results showed that this was a metastable state of the Si donor. It was explained in terms of the intermediate state of a negative-U DX center, and a metastable negative-U configuration of the Si donor. A further photo-induced deep-level transient spectroscopic peak was observed within a narrow Al composition range, and was attributed to the shallowest DX level of the 4 distinct DX levels that originated from different differing environments of the donors.

Y.B.Jia, H.G.Grimmeiss: Journal of Applied Physics, 1996, 80[6], 3493-502