Intrinsic Electron Accumulation at Clean InN Surfaces

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 $\Gamma$-point conduction band minimum in wurtzite InN. As a result, surface Fermi level pinning high in the conduction band in the vicinity of the $\Gamma$ 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 $2.5(\pm 0.2)\times {10}^{13}{\mathrm{c}\mathrm{m}}^{-2}$ and a surface Fermi level of $1.64\pm 0.10\mathrm{e}\mathrm{V}$ above the valence band maximum.