Deep-center photoluminescence in undoped semi-insulating GaAs: 0.68 eV band due to the main deep donor

The 0.68 eV photoluminescence band present in undoped semi-insulating GaAs crystals has been studied with the change of temperature. It is shown that the 0.68 eV band is due to the radiative transition involving a main deep donor and the valence band. The origin of the donor is of an intrinsic origin and may involve an As antisite defect. It is found that the donor level does not change in energy with respect ot the valence band at T = 4–300 K. The donor level is found to be at 0.73 eV from the conduction band at T = 4 K.