On the impact of lateral inhomogeneity on photoconductance decay lifetime measurements

Abstract

The photoconductance decay technique is commonly used to measure the injection-dependent effective lifetime of excess charge carriers in crystalline silicon allowing for an in-depth analysis of excess charge carrier recombination. Its working principle relies on eddy currents induced by a coil within a certain sensitivity region in which the sample properties, in particular the excess charge carrier lifetime, should be homogeneous as the technique only yields a laterally integrated result. Within this paper it is discussed in theory, simulation and experiment how lateral inhomogeneity of excess charge carrier lifetime impacts the result of the lifetime measurement. It is shown that extended regions of strongly different bulk lifetime result in abnormal injection-dependent lifetime curves whose shape depends on the applied measurement and analysis conditions. Experimental results hereby validate the presented theoretical approach. It is furthermore discussed, how continuous distributions of lifetime, like a lateral gradient in lifetime, may conceal to some degree the abnormal shape and may lead to erroneous analysis results. Finally it is demonstrated that lateral inhomogeneous surface passivation results in distorted lifetime curves as well.