ИСТИНА

Photovoltage measurements on prepared silicon surfaces yielding information on surface state morphology and dynamics are reported. Surface photovoltage changes resulting from excitation using both tunable and fixed wavelength sources were monitored using a Kelvin Probe apparatus. Both sub-bandgap and super-bandgap excitation wavelengths were used on an array of doped and undoped Si surfaces. The majority of the measurements were conducted with the samples at atmospheric pressure. A simple theoretical model of finite crystal solid surfaces helped elaborate the essential difference between work function and the local work function determinations. Formulae for surface potential, surface state population and charge carrier relaxation resulting from selective excitation were derived using Shockley and Reed theory. The presence of atmospheric constituents chemisorbed on the surfaces was also investigated. Large photovoltage signals induced by laser excitation revealed optical saturation effects that could be related to surface potential information and work function evaluation. Narrow surface photovoltage and photoconductance spectral signatures of cleaved Si(111) samples observed at reduced temperature and pressure provided additional insight into the contribution of sub-bandgap excitation processes involving surface states.