Surface bias voltages induced on a scanning tunnel microscope (STM) junction illuminated with laser radiation are spatially resolved for silicon surfaces. Surface photovoltages of ∼0.3 V for Si(111)-(7×7) and <0.1 V for Si(001)-(2×1) are observed with large reductions in the vicinity of surface/subsurface defects associated with midgap states. These reductions, attributed to a variation in the recombination rate, have typical surface screening lengths that are less than those found in the bulk. A small, atomically varying signal of 3–5 mV is also observed and is due to spatial variations in rectification efficiency rather than photovoltage.
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Kuk et al. (1991) studied this question.