Mobility-lifetime product of photoexcited electrons in GaAs

Application of large DC and AC fields to undoped semi-insulating GaAs to enhance its photorefractive performance leads to improvement compared to no applied field, but the improvement is not nearly as large as predicted theoretically when zero-field values of the mobility-lifetime product are used in the calculations. For example, Fig. 1 shows the gain coefficient as a function of grating period when an AC electric field is applied to the sample.1 The dashed lines are theoretical predictions based on a mobility of 5000 cm2/V-sec (from the Hall mobility of an adjacent sample) and a carrier lifetime of 30 nanoseconds (based on literature values for the recombination cross section of electrons to the EL2* level2). The solid lines are based on a mobility lifetime product four orders of magnitude smaller.