The decay rate of transient photocurrents in semiconductors

In many semiconductors, including even some samples of amorphous hydrogenated silicon, the transient photocurrent observed in time-of-flight measurements does not show anomalous dispersion, but rather is approximately constant up to a well-defined transit time t_T, after which it tends to decay exponentially with time. Most analyses of the experimental results consider only the transit time and its dependence on temperature, electric field and sample thickness. We show that useful extra information can readily be obtained from the rate of decay of the photocurrent at times longer than t_T, and from the temperature dependence of this decay rate.