The transitions which were associated with magnetic circular dichroism of absorption in GaAs were investigated by studying the spectrum as a function of stoichiometry in AlGaAs which had been grown at low temperatures by means of molecular-beam epitaxy. The principal result was that the spectrum of the singly ionized As antisite could be explained in terms of the valence-band model. That is, the optical transitions were from the valence band to the A1 ground state. A competing, internal transition, model was refuted. The stoichiometry dependence also suggested that the observed diamagnetic spectrum of the neutral As antisite could be linked to the zero-phonon line of the optical-absorption spectrum.
A.Prasad, P.Stallinga, X.Liu, E.R.Weber: Physical Review B, 1998, 57, R4214-7