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Photoluminescence from Uudoped GaAs under Applied Electric Field: The Transition Mechanism at High Excitation Levels near 77 K

The emission process in undoped GaAs has been studied near 77K under high optical excitation. We found that the density of state under highly-excited conditions forms the tail state, based on an impact ionization-model by accelerated free carriers under an electric field up to 3 kV/cm. It has been found that the luminescence spectrum is well understood by taking into account the band tail in addition to the band-gap reduction due to the many body effects. Stimulated emission is dominated by the transition between the conduction band tail and the valence band. Furthermore, detailed discussions are given on the origin of the band tailing.