Surface photovoltage on Si(111)‐(7×7) probed by optically pumped scanning tunneling microscopy

Scanning tunneling microscopy (STM) is combined with optical excitation techniques to probe spatially resolved, nonequilibrium electronic transport processes at Si(111)‐(7×7) surface. Photoexcited carriers separate in the subsurface space‐charge region, producing a surface photovoltage which is detected using the STM tip as a potentiometer. While the photovoltage is uniform on well‐ordered regions of Si(111)‐(7×7), strong decreases are observed near virtually all defects. Differences in the functional dependence of the photovoltage on the illumination intensity are also observed. The spatial dependence of the photovoltage primarily results from spatial variations in the local surface recombination rate.