Analysis of nondispersive time-of-flight transients

Nondispersive time-of-flight (TOF) photocurrent transients have been described well in the theoretical photocurrent transient equation (PTE) based on the fact that a carrier packet drifts at a constant velocity and is spread by diffusion and the top electrode acts as a reflecting and partially absorbing wall and the counter electrode acts as an absorbing wall. In order to verify the PTE, we try to explain the anomalous behavior of μkₑx, obtained from the time derived from the intersection of the asymptotes to the plateau and tail of the transient, and the tail-broadening parameter (Wₑₓ). Using the PTE, we derive both the mobility (μkcal), obtained from a kink in the TOF measurement, and the tail-broadening parameter (Wcal) as functions of the drift velocity, the diffusion coefficient, and the sample thickness. The dependences of μkcal and Wcal on the electric field and the sample thickness agree well with those of μkₑx and Wₑₓ. These results verify the PTE, and suggest that fitting of the PTE to the TOF transient is a suitable measurement of the drift mobility.