TIME-DEPENDENCE OF PHOTOVOLTAIC SHIFTS IN PHOTOELECTRON-SPECTROSCOPY OF SEMICONDUCTORS

Photovoltage-induced peaks shifts in photoelectron spectroscopy (PES) were recently shown to be important in studies of semiconductor interface formation [M. H. Hecht, Phys. Rev. B 41, 7918 (1990)]. In that process, the photons used to probe the sample were shown to cause a reduction in surface band bending, hence shifting the spectrum in energy. In this paper it is shown that the time dependence of the charging and discharging process can have an important influence on experimentally observable phenomena. Since the charging process is very fast, the effective photocurrent in a pulsed-synchrotron-radiation experiment may be orders of magnitude higher than previously assumed. Using a simple model of the discharge profile it is shown that the photovoltage persists on a time scale that is macroscopic under typical PES conditions. Finally, a noncontacting method for determining equilibrium surface band bending is proposed.