Quantitative evaluation of grain boundary activity in multicrystalline semiconductors by light beam induced current : an advanced model

Abstract

We present an advanced analytical model which applies to light beam induced current contrast profiles to determine reliably the effective surface recombination velocities Seff of grain boundaries GBs and diffusion lengths Ldiff in the grains, in cases where a GB is close to the studied one or when Ldiff of the neighboring grain differs. We introduce additionally a new method for a very accurate determination of the plateau value of the investigated linescan and make use of simultaneously fitting GB profiles measured at various laser wavelengths both aiming at increasing the accuracy of the Ldiff determination. Through several special case investigations, the various applications and limitations of the model are demonstrated.We discuss the influence of the electrical parameters of the semiconductor on the various zones of the profile as well as the influence of measurement technique parameters on the experimental profile and point out the need of an accurately determined small laser beam radius to ensure a reliable extraction of Seff. We discuss the occurring discrepancy between fit and measured data and show that it gives hints about particular material features and the reliability of the extracted parameters. We finally point out the possibility of determining Ldiff in small grains. This model thus allows more realistic GB situations to be investigated.