Minority-carrier lifetime mapping in silicon using a microprocessor-controlled flying-spot scanner

Abstract

An automatic flying-spot scanner with fast data acquisition is described, which is used for the characterisation of semiconductor samples. The measurement system can be used for the visualisation of resistivity and lifetime inhomogeneities across a semiconductor sample, information about surface conditions (mainly surface-recombination velocity) and for the measurement of minority-carrier lifetime in discrete lateral points resulting in lifetime maps of the sample. The technique described utilises the photocurrent collected at a reverse biased rectifying junction at the rear side of the sample. The authors present measurements of lifetime in silicon p⁺n-junctions. The lifetime distributions are visualised as maps of the absolute lifetime values against position and as computed blackness-modulated maps. The latter type of map provides an easier analysis of the measurement than the former. Necessary surface precautions are also discussed.