The Role of EL2 for the Mobility-Lifetime Product of Photoexcited Electrons in GaAs

Abstract

abstractThe mobility lifetime products for photo-electrons in semi-insulating GaAs, which fit successfully the results of photorefractive studies undertaken in the presence of electric fields are three orders of magnitude smaller than those inferred from transport measurements or from the photorefractive effect with no applied electrical field. Consideration of enhanced recombination via EL2 effective-mass states linked to the L-conduction band minimum allows us to fit the dependence of the photorefractive beam coupling gain coefficient on the grating period for both AC fields and moving gratings. A cascade-capture process, which is three orders of magnitude faster than recombination by multiphonon emission from the Γ band to EL2, leads to greatly reduced mobility-lifetime products for field strengths greater than 1 kV/cm. Our results establish the dominant influence of the EL2 defect properties on the recombination processes essential for modelling and optimizing the photorefractive effect in semi-insulating GaAs.