Flying-spot scanning images of a chemically etched p-type polycrystalline Si wafer, 60 mm in diameter, are obtained nondestructively using the AC photovoltage excited by a visible photon beam chopped at 2 kHz. The AC photovoltage is concluded to be the surface photovoltage correlated with the native oxide layer. After thermal annealing in N 2 ambience at 850 degrees C for 60 min, the surface image drastically changes. This might be due mainly to fixed oxide charge modification and partly to variation in the minority carrier diffusion lengths.
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Munakata et al. (1983) studied this question.
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