Intrinsic Electron Accumulation at Clean InN Surfaces

Abstract

The electronic structure of clean InN(0001) surfaces has been investigated by high-resolution electron-energy-loss spectroscopy of the conduction band electron plasmon excitations. An intrinsic surface electron accumulation layer is found to exist and is explained in terms of a particularly low $\ensuremath{\Gamma}$-point conduction band minimum in wurtzite InN. As a result, surface Fermi level pinning high in the conduction band in the vicinity of the $\ensuremath{\Gamma}$ point, but near the average midgap energy, produces charged donor-type surface states with associated downward band bending. Semiclassical dielectric theory simulations of the energy-loss spectra and charge-profile calculations indicate a surface state density of $2.5\text{ }(\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}{10}^{13}\text{ }{\mathrm{c}\mathrm{m}}^{\ensuremath{-}2}$ and a surface Fermi level of $1.64\ifmmode\pm\else\textpm\fi{}0.10\text{ }\mathrm{e}\mathrm{V}$ above the valence band maximum.