PHOTOREFRACTIVE EFFECT IN GAAS AT LOW-TEMPERATURE - INFLUENCE OF THE METASTABLE STATE OF THE EL2 DEFECT

We present here a theoretical and experimental analysis of photorefrac tive two-beam coupling in undoped GaAs as a function of temperature. T hree major features are experimentally observed, firstly, a change of sign of the photorefractive beam coupling gain around 150 K, secondly, an enhancement of the space charge field by a factor 2 compared to th e diffusion field and, finally, a strong peak of the absorption gratin g amplitude around 150 K. A photorefractive model is established that includes the metastable state of the EL2 defect with its optical prope rties (optical generation and optical recovery). It predicts all obser ved features correctly and is in good agreement with the experimental data.