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 (+/-0.2)x10(13) cm(-2) and a surface Fermi level of 1.64+/-0.10 eV above the valence band maximum.

We present ab-initio calculations of excited-state properties within single-particle and two-particle approaches in comparison with corresponding experimental results. For the theoretical treatment of the electronic structure, we compute eigenvalues and eigenfunctions by using a spatially nonlocal exchange-correlation potential. From this starting point, quasiparticle energies within the fully frequency-dependent G0W0 approximation are obtained. By solving the Bethe-Salpeter equation, we evaluate optical properties, including the electron-hole attraction and the local-field effects. The results are compared with experimental spectra from soft X-ray emission, as well as from X-ray photoelectron spectroscopy or ellipsometry measurements. In more detail, we compute the valenceband densities of states, bound excitons, and the dielectric function. For the latter, we discuss both the absorption edge and higher critical points.

High-resolution electron energy-loss spectroscopy ͑HREELS͒ has been used to study the surface-plasmon excitations in degenerate n-type InAs ͑110͒ surfaces prepared by atomic hydrogen cleaning ͑AHC͒, and a range of different argon-ion bombardment and annealing ͑IBA͒ procedures. Using semiclassical dielectric theory simulations of the HREEL spectra, and modified Thomas-Fermi approximation charge profile calculations, the dependence of the bulk carrier concentration, accumulation layer profile, plasmon lifetime, carrier mobility, and spatial dispersion on the IBA conditions, was determined. The results from the IBA surfaces were compared with those from damage-free surfaces prepared by AHC. The density of created defects increased both as a function of the bombardment angle when varied from grazing to normal incidence for 500 eV IBA, and when the bombardment energy was increased from 500 to 1500 eV. The band bending and the potential-well widths used to simulate these data, were found to be dependent upon the bombardment energy. However, these parameters changed proportionally, resulting in the surface-state density remaining independent of the surface preparation method.