Study on the time decay of excess carriers in solar silicon

An understanding of the measured excess carrier decay in solar silicon is needed for a meaningful characterization of the material quality by this method. This paper studies the time decay of excess carriers after laser pulse excitation in solar silicon. For this material, which exhibits a high density of different defects, a simplified approach to solve the diffusion equation of the excess carriers can be taken. We calculate the time decay of the excess carriers numerically by using an appropriate model of the bulk minority carrier lifetime. These calculations are subsequently compared to experimental data, which are obtained by measuring the photoconductance decay using reflected microwaves in surface passivated solar silicon wafers. A very good agreement between theoretical and experimental results gives the base for further evaluation of interstitial iron and minority carrier traps using the excess carrier decay.