Measurement of Minority Carrier Lifetimes using AC Photovoltages Excited by Two Photon Beams of Different Wavelengths

Results of using two chopped photon beams with wavelengths of 1.15 and 0.6328 µm, to measure the ac surface photovoltages of a Si wafer and a bar while changing the chopping frequency are presented. The ratio of ac surface photovoltages with 1.15 µm to that with 0.6328 µm vs frequency represents the frequency dependence of the photocurrent. From the frequency at the knee point that appears on the frequency dependence curve of the ratio, the lifetimes for minority carriers in a Si wafer and a bar are obtained. The observed values of 9.65 µs and 86 µs agree well with the 9.7 µs and 90 µs obtained by conventional methods.