A study of the initial photocurrent due to pulsed light absorbed in finite thickness

Abstract

It is often assumed that light is absorbed in an infinitesimally thin region at the surface in analyzing the photocurrent in pulsed-light measurements. However, the incident light is generally absorbed within a finite depth from the surface. The effect of such finite light penetration on the initial photocurrent for a trap-free material is examined here assuming an initial exponential distribution of carriers in space and simple bulk recombination processes. It is shown that the initial photocurrent consists of three parts: a constant current due to carriers which get photoinjected into the sample, a current due to carriers of opposite polarity which are collected at the illuminated surface, and a current due to carriers which recombine. The latter two currents decay rapidly to zero resulting in a total current decay. Cases which approximate monomolecular recombination and bimolecular recombination are treated in detail. The results indicate that experimental observation of this initial current decay will yield information regarding free-carrier generation efficiency, recombination processes, and the mobility of the second carrier. © 1972 The American Institute of Physics.