Determination of the surface band bending in InxGa1−xN films by hard x-ray photoemission spectroscopy

Core-level and valence band spectra of In x Ga1-x N films were measured using hard x-ray photoemission spectroscopy (HX-PES). Fine structure, caused by the coupling of the localized Ga 3d and In 4d with N 2s states, was experimentally observed in the films. Because of the large detection depth of HX-PES (∼20 nm), the spectra contain both surface and bulk information due to the surface band bending. The In x Ga1-x N films (x = 0-0.21) exhibited upward surface band bending, and the valence band maximum was shifted to lower binding energy when the mole fraction of InN was increased. On the other hand, downward surface band bending was confirmed for an InN film with low carrier density despite its n-type conduction. Although the Fermi level (EF) near the surface of the InN film was detected inside the conduction band as reported previously, it can be concluded that EF in the bulk of the film must be located in the band gap below the conduction band minimum.