PHOTOCONDUCTIVITY TRANSIENTS AND PHOTOSENSITIZATION PHENOMENA IN SEMIINSULATING GAAS

A model is proposed for the photoconductivity transients and the photosensitization in semi-insulating GaAs induced by low-intensity light at low temperatures. During photoconductivity transients, the lifetime of free carriers is shown to be a time-dependent quantity, determined mainly by the trapping processes, recombination being negligible. Photosensitization and thermal restoration are explained by the filling and emptying of deep traps. Contrary to some other explanations, in this model it is not necessary to utilize the metastability of EL2 or other defects. The model is verified experimentally by an original use of the thermally stimulated current method. It is also possible to determine values of capture cross sections for dominant traps.