The kind of defects and their concentration have a significant impact on photorefractive phenomena taking place within the structure of semi-insulating GaAs / AlGaAs multiple quantum wells. In this paper, the impact of donor-to-acceptor concentration ratio on the grating in photorefractive two-waves mixing was examined. The formation of the space charge field for different defect concentrations as well as different external electric field intensities are analyzed.

Nonlinear transport of hot electrons in semi-insulating GaAs / AlGaAs quantum wells significantly affects their photorefractive properties. In case of two waves mixing, this influence consists, among others, in an increased shift of photorefractive grating relative to light intensity distribution. The influence of nonlinear transport on grating recording time is less examined experimentally and theoretically. This study compares numerical and analytical solutions describing grating dynamics in approximation of small fringe contrast. The influence of nonlinear electron mobility on space-charge field was examined depending on external electric field intensity and on the grating constant. It was found that in the electric field range below 20 kV/cm, the nonlinear transport of electrons does not shorten the grating generation time.

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Abstract-Semi-insulating GaAs/AlGaAs multiple quantum wells are photorefractive materials with high sensitivity and short response time. Semi-insulation of these structures is commonly obtained by proton implantation. We present the measurements of photoconductivity in the samples with different proton doses. The results were compared to the theoretically predicted relationship between photoconductivity and the donor to acceptor concentration ratio. This allows to estimate the impact of proton dose on deep donor concentration.

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