Magnetic resonance studies of group IV and VI donors in Ga1-xAlxAs

Abstract

The magnetic resonance results for the group IV (Si, Sn) and group VI (S, Se, Te) donors in GaAlAs alloys are reviewed. For the donors Si, S, Se, Te the DX deep donor state has apparently not been observed; the paramagnetic state generated by photoexcitation has been attributed to the X conduction band derived effective-mass (EM) state. On the contrary recent results for Sn, where the central hyperfine interaction could be resolved, demonstrate clearly that for Sn the paramagnetic donor state is not EM-like; it is attributed to the neutral charge state of the DX centre. A comparison of the photoexcitation process and the associated persistent photoconductivity gives a strong indication for a negative-U DX ground state. It is shown that recent deep-level transient spectroscopy results further support this assignment. However, it is unclear why in some cases (Si, S, Se, Te) apparently only the EM states are observed and not the deep donor state, whereas in the case of Sn the situation is reversed.