We derive a simple formula for the width of the quasielastic peak in inelastic electron scattering from accumulation and inversion layers at semiconductor surfaces. As an application, it is shown that for the (2×1) reconstructed Ge(111) surface, the Fermi level (at room temperature) is pinned 140 meV above the surface valence-band edge ($E_{\mathrm{vs}}$). This result differs from the prevailing opinion that the pinning occurs right at $E_{\mathrm{vs}}$. For temperatures T<300 K, the pinning position varies linearly with temperature in such a way that the pinning occurs at $E_{\mathrm{vs}}$ at T=0 K.

• Received 6 June 1989

DOI:https://doi.org/10.1103/PhysRevB.40.7819