Determination of the Recombination Velocity on Unequal Surfaces of Silicon Wafers from Two-Spectrum Excited Quasi-Steady-State Photoconductance

Abstract

The minority charge carrier lifetime measured using the quasi-steady-state photoconductance (QSSPC) technique for a silicon wafer provides quantitative information about surface and bulk recombination. However, conventional methods used to determine the surface recombination velocity from a measured effective lifetime are mostly limited by assuming the identical passivation quality of both surfaces and a constant lifetime throughout a sample. In order to further separate the surface recombination velocities of the two unequal surfaces of a silicon wafer, we present an approach to analyze the decay curves of excess minority charge carriers illuminated with two different spectra. This approach is based on a numerical calculation of the one-dimensional continuity equation using the Crank–Nicholson finite difference method. By performing QSSPC measurements with LG700 and SP850 filters, the surface recombination velocities of the front and back surfaces of a set of passivated and bare silicon wafers, S1 and S2, were determined via our analysis method. The excess charge carrier density and the bulk lifetime distributions for wafers of different resistivities are theoretically demonstrated.