Electron-phonon-plasmon interaction in MBE-grown indium nitride - A high resolution electron energy loss spectroscopy (HREELS) study
We studied InN (0001) grown by plasma assisted molecular beam epitaxy (PAMBE) with high-resolution electron energy-loss spectroscopy (HREELS) after vacuum transfer thus avoiding any further surface preparation. We were able to detect for the first time besides the Fuchs-Kliewer surface phonon ω0 two plasmarons ω– and ω+, which originate from the coupling between surface optical phonons ωSO and plasma oscillations of free electrons resulting from the surface accumulation layer and/or the bulk conduction band. Using dielectric theory we get new insight into the space charge regime of InN grown by MBE. We choose an approach that reaches far beyond the accumulation layer regime. Using a very wide primary beam energy regime from 1 eV up to 200 eV, the depth of information can be varied from extremely surface sensitive to bulk sensitive. Best agreement has been obtained for a downward band bending of 0.9 eV and a peak accumulation layer density of 6.5 × 1019 cm-3 at 2 nm beneath the surface with an unintentional doping of the bulk of 1 × 1019 cm-3. The sheet density of the ionized surface states is determined to Nss = 1.8 × 1013 cm-2 from the self-consistent calculation of the conduction band profile. The presented results provide important information for future InN-based devices. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)