ABSENCE OF DICHROISM FOR THE DX OPTICAL-BLEACHING TRANSIENTS IN AL0.35GA0.65AS-TE

We have attempted to observe preferential ground- to metastable-state conversion by polarized light of a subgroup of DX centers in Al0.35Ga0.65As:Te. The expected effect was calculated for transition moments either parallel or perpendicular to the defect symmetry axes for C3-upsilon, D2d, C2-upsilon, and C1h defect symmetries. The experiment was performed by monitoring the transient transmission through an optically thick specimen for various polarization sequences. We found no statistically significant effect, and the theoretical expectations fall well outside the limits determined from the experimental uncertainty. We conclude that the transition moment for the optical conversion of the DX center is very nearly isotropic, which leads to one of two possibilities. Either both parallel and perpendicular dipoles accidentally contribute simultaneously to the DX-center ionization band, or there is no large symmetry-lowering distortion at the DX center.