STM MEASUREMENTS OF PHOTOVOLTAGE ON SI(111) AND SI(111)-GE

Photovoltages were measured with a tunneling microscope for Si(111)7 x 7 and Si(111): Ge5 x 5 surfaces. Over 100 angstrom images, the photovoltages were uniform within 10 mV, despite missing surface atoms or adsorbed residual gas atoms. Cross-correlation between photovoltage and topograph images shows that the atomically varying part of the photovoltage is smaller than 0.1 mV. The average photovoltages were large and consistent with the band structure of the surfaces. We discuss error sources in photovoltage measurements and differences with previous publications.