In adlayers on c-plane InN surfaces: A polarity-dependent study by x-ray photoemission spectroscopy

The surfaces of In- and N-polarity InN grown by molecular-beam epitaxy 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 InN surfaces have been found to be terminated by In adlayers, in agreement with the predictions of previous first-principles calculations. The In- and N-polarity surfaces are terminated by similar to 3.4 and similar to 2.0 ML of In, in each case 1 ML more than for Ga on GaN surfaces under metal-rich growth conditions. The valence band XPS indicates a valence band maximum to surface Fermi level separation of 1.32 +/- 0.10 eV for both In- and N-polarity InN surfaces, indicating that the surface space charge is independent of polarity and, unlike for GaN, is not significantly affected by spontaneous polarization. This is due to the In coverage on the surface of InN of both polarities being sufficient to efficiently screen the polarization charge.