Analysis of nondispersive time-of-flight transients

Abstract

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 ${\ensuremath{\mu}}_{k_ex},$ obtained from the time derived from the intersection of the asymptotes to the plateau and tail of the transient, and the tail-broadening parameter ${(W}_{\mathrm{ex}}).$ Using the PTE, we derive both the mobility $({\ensuremath{\mu}}_{k_cal}),$ obtained from a kink in the TOF measurement, and the tail-broadening parameter ${(W}_{\mathrm{cal}})$ as functions of the drift velocity, the diffusion coefficient, and the sample thickness. The dependences of ${\ensuremath{\mu}}_{k_cal}$ and ${W}_{\mathrm{cal}}$ on the electric field and the sample thickness agree well with those of ${\ensuremath{\mu}}_{k_ex}$ and ${W}_{\mathrm{ex}}.$ These results verify the PTE, and suggest that fitting of the PTE to the TOF transient is a suitable measurement of the drift mobility.