Changes in the positron-electron momentum distribution in GaAs brought about by chopped light

Abstract

We report on an attempt to observe the EL2 → EL2* transition in semi-insulating GaAs using Doppler broadening of annihilation radiation spectroscopy. Unlike the original observation of this transition using positron annihilation spectroscopy, the present method has sought to observe the production of EL2* through a light chopping experiment, where on the half cycle of illumination the EL2* state is formed and on the second half cycle the EL2* thermally quenches back to EL2. While results are at a preliminary state we have obtained evidence for the production of EL2* from the broad-band emission of a Xenon lamp. While calculations suggest that we should be able to see the EL2* from the IR emission (1.3eV) of GaAs light emitting diodes we have not yet been able to achieve this. Reasons why are discussed.