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

We derive a simple but general formula which describes the width of the quasielastic peak in inelastic electron scattering from doped semiconductors and 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 of 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.