Transport correlation coefficients and photoconductive switching

The use of a retarded Langevin equation for the development of a simple model of a photoconductive switch is described. This model allows the the accurate determination of carrier transport transients in the switch provided that certain commonly made assumptions concerning spatial homogeneity remain valid and an appropiate optical pulse energy and wavelength are chosen. The model utilizes velocity autocorrelation functions which could be estimated by Monte Carlo techniques or potentially measured by applying the model to appropiate experimental data. The validity of the model is demonstrated for wavelengths in which carriers are generated somewhat below the threshold for intervalley scattering. A mechanism by which an applied field can actually delay the initial rise in a photocurrent in a subpicosecond photoconductive experiment is described as well.