Electron energy loss study of the space charge region at semiconductor surfaces.

We derive a simple but general formula for the width of the quasielastic peak in inelastic electron scattering from doped semiconductors which is used to analyze the space charge region at the GaAs(100) surface. The analysis shows that the Fermi level at the surface is pinned 0.8 eV below the conduction band edge in the absence at any metal or oxide overlayer and that the free carrier concentration in the near surface region can be readily reduced from the bulk value. This reduction is caused by the surface preparation (sputtering and annealing) which introduces acceptor point defects in this region of the GaAs crystal.