Above Band-Gap Excitation Process of the 0.6 eV Luminescence Band in GaAs

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Abstract
The transition mechanism of the 0.6 eV luminescence band, observed commonly in undoped semi-insulating GaAs crystals under the above band-gap excitation (AGE), has been investigated by photoluminescence excitation spectroscopy. We show that the 0.6 eV AGE band consists of the 0.63 and 0.68 eV bands with the same recombination processes as in the case of the below band-gap excitation. The peak of the 0.6 eV AGE band shifts with the excitation photon energy as a result of the discontinuity in the excitation spectrum of the 0.68 eV band. This discontinuity is explained by the presence of the excitation process via the excited state of the EL2 level resonant with the conduction band.