A technique for separating bulk and surface lifetimes in the analysis of photoconductance decay measurements

Photoconductance decay measurements are frequently used to measure the lifetime of silicon wafers prior to processing and occasionally after various processing steps have been performed. It is an easy to use rapid measurement. However, the usual analysis of the data results in a determination of an "effective" lifetime which includes the effects of both bulk and surface recombination. This paper describes the measurement conditions and the analysis procedures which allow one to analyze photoconductance decay data to obtain the bulk lifetime and the surface recombination of the two surfaces rather than just the "effective" lifetime. Since the technique is contactless and does not require any additional processing or modification of the wafer, it is particularly promising as a process monitoring tool.