In-adlayers on non-polar and polar InN surfaces: Ion scattering and photoemission studies

The surface structure of In-polarity c-plane InN has been investigated by low energy ion scattering spectroscopy. Comparison of ion scattering spectra recorded along the [1 0 0 0] azimuth with model calculations indicates that the clean In-polarity c-plane InN surface is terminated by In-adlayers with a laterally contracted topmost In layer. This is consistent with previous X-ray photoemission and electron diffraction results. Additionally, the surface properties of a-plane InN have been investigated using core-level and valence band X-ray photoemission spectroscopy (XPS). From the ratio of the In and N core-level XPS signal intensities, the clean a-plane InN surface has also been found to be terminated by In-adlayers. Photoemission measurements of the valence band maximum to surface Fermi level separation for a-plane InN indicate the existence of an electron accumulation layer at the surface. This observation of electron accumulation at non-polar InN surfaces in the presence of In-adlayers is in agreement with the predictions of previous first-principles calculations.