A PHOTOLUMINESCENCE STUDY OF THE EFFECTS OF HYDROGEN ON DEEP LEVELS IN MBE GROWN GAALAS-SI

We present a study on low-temperature photoluminescence (PL) of Si-doped Ga1-xAl(x)As (n approximately 1 x 10(17) cm-3, 0.2 less-than-or-equal-to x less-than-or-equal-to 0.5) grown by MBE in the presence and in the absence of a hydrogen backpressure, and post-growth hydrogenated or not, by exposure to a hydrogen plasma. The PL spectra of GaAlAs grown without hydrogen are dominated by transitions involving relatively deep donors and/or acceptors independently on whether the material is post-growth hydrogenated. On the contrary, the spectra of GaAlAs grown in the presence of hydrogen are characterized by recombinations related to excitons and/or to shallow donors and acceptors. Both the in-situ and the ex-situ processes result in Pl efficiency enhancements, which are definitely larger (by a factor of up to 20) when the former treatment is used. All of the above results suggest that the ex-situ and the in-situ treatments may affect deep levels of different origin, such as DX centers (related to the band structure of the semiconductor) and levels associated to Al-O complexes, respectively.