Separation between Surface and Volume Decay Times of Photoconductivity in p-Type Silicon Wafers

Excess photocarriers excited in silicon wafers are annihilated both in surface and volume regions independently of each other. When a photoconductive decay curve obtained with the microwave-detected photoconductive decay method is concave in semi-logarithmic scale, those two decay times in the different regions can be separately derived from the experimental data on assuming two independent exponential functions for the annihilation of excess carriers. The separation procedure can be completed using a commercially available computer code. The surface decay times vary from more than 95 to 13 µs when the p-type silicon wafer rinsed with a hydrofluoric acid solution is kept exposed to the room air, while the volume decay times of around 1.7 µs thus obtained are almost constant and quite reasonable in comparison with the theoretically expected one.