The optical modulation of the transmission of low energy electrons: GaP surface sensitivity

Abstract

When electrons are incident on a solid surface, some are backscattered and some are transmitted into the bulk of the material. This paper examines both the total transmitted current and the optically modulated component of this transmitted current for GaP. Both are dependent on the incident electron energy and this dependence is sensitive to the surface conditions. For example, Ar bombardment of the GaP surface results in a large increase in the optically modulated current compared to the polished GaP samples at higher incident electron energies (10–100 eV). Etching the GaP sample in HCl also results in a similar increase in the optically modulated current. In addition, both the HCl etch and/or Ar bombardment of the GaP surface change the temperature dependence of the optically modulated current. This surface sensitivity forms the basis for a new surface spectroscopic technique which probes the opto-electronic properties of semiconductor surfaces. A theoretical model involving the photovoltaic modulation of electron transmission is presented which can account for the observed experimental results.