Kinetics study on the mechanism of zero-bias photocurrent in semi-insulating bulk GaAs

The mechanism of zero-bias photocurrent (ZBPC) in semi-insulating GaAs:Cr bulk crystals is studied by kinetics measurements. A simple quantitative model describing the time behaviour of the photogenerated electron concentration is developed. This model confirms our previous qualitative suggestion [J. Electrochem. Soc. 141 (1994) 2533] that the ZBPC is due to the random defect-density fluctuations (RDDF) in the material investigated. The ZBPC polarity inversion observed in some ranges of ZBPC low temperature spectra [J. Electrochem. Soc. 141 (1994) 2533] is also explained in frame of the model proposed. It is shown that the negative ZBPC is carried out by electrons driven by electric fields connected with previously generated holes trapped in the potential ‘hills’ of the valence band.