Calculation of two-photon conductivity under nanosecond and picosecond pulse excitation in semiconductors

Abstract

It has been the usual practice to solve the continuity equation for the case of steady excitation and presume that the same results are valid for pulse excitation of the photoexcited carriers. However, it has been shown in the present analysis that this assumption is valid for the exciting pulse which is of longer duration than the mean lifetime τ of the photoexcited carriers. In the case of excitation of photoconductivity by picosecond pulses, which are now available from the mode-locked laser system, the pulse duration is much smaller than τ and the results of steady-state excitation are no longer applicable. Moreover, the magnitude of the photoconductivity depends on the pulse duration T and is independent of τ. In fact, the photoconductivity is found to exhibit a transient behavior.