Bound exciton spectra in semi-insulating GaAs

We report sharp photoluminescence lines in semi-insulating GaAs diffused with small concentrations of lithium. We attribute a new line at 1.466 eV to an exciton bound to a neutral, electrically inactive, deep defect involving lithium, lines at 1.508 and 1.510 eV to excitons bound to accepters, while a new, broad peak around 1.501 eV could be a donor-to-acceptor transition to a shallower acceptor than previously observed in GaAs. Possible identities of the defects responsible for these transitions and their relation to lithium will be discussed.