Photoluminescence and photoluminescence excitation spectroscopy of the EL2 emission band in GaAs

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Abstract
Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy have been performed on the 0.635-eV emission band in GaAs. Recently, this band has become of increased importance as a consequence of having been associated with the main electron trap (EL2) in GaAs. All samples studied exhibit a strong peak in the PLE at 1.5 eV, whose characteristics indicate that this emission band arises from deep donor-acceptor pair recombination. We also observe a related PL band at 0.68 eV which does not exhibit the 1.5-eV peak in the PLE and is attributed to recombination between a deep level and a hole in the valence band. The PLE spectra for both of these emission bands exhibit oscillations resulting from the resonance cooling of hot electrons by the emission of LOΓ phonons. This phenomenon, which has apparently never before been reported for such a deep level, suggests that an intermediate shallow donor state is involved in the recombination processes for both of these PL bands. We will discuss the relationship between our measurements and various microscopic models which have been proposed to describe the EL2 defect center.