Contactless nondestructive technique for the measurement of minority-carrier lifetime and diffusion length in silicon

A nondestructive contactless technique which allows high-resolution point-by-point measurement of minority carrier lifetime and diffusion length in silicon, without the need for special structures, is described. Excess carriers are generated at a known rate by a 1 mW He-Ne laser beam focused to a fine spot on the silicon surface. The resulting total carrier number, which is inversely proportional to the recombination time, is detected by a novel infra-red emission technique. Spatial variations of lifetime have been measured, and small regions of high recombination located. Many of these can be associated with oxidation-induced stacking faults. The diffusion length is measured directly by observing the variation of carrier concentration with distance away from the point of injection. The technique is applicable to other semiconductors, and will be particularly valuable where it is difficult to make electrical contact.