Fermi-level Pinning and Intrinsic Surface States of Al1−xInxN(101¯) Surfaces

The electronic structure of Al1−xInxN(101¯0) surfaces is investigated by cross-sectional scanning tunneling spectroscopy and density functional theory calculations. The surface exhibits empty Al and/or In-derived dangling bond states, which are calculated to be within the fundamental bulk band gap for In compositions smaller than 60%. The energy of the lowest empty In-derived surface state is extracted from the tunnel spectra for lattice-matched Al1–xInxN with In compositions of x = 0.19 and x = 0.20 to be EC − 1.82 ± 0.41 and EC − 1.80 ± 0.56 eV, respectively, in good agreement with the calculated energies. Under growth conditions, the Fermi level is hence pinned (unpinned) for In compositions smaller (larger) than 60%. The analysis of the tunnel spectra suggests an electron affinity of ∼3.5 eV for nonpolar lattice-matched Al1–xInxN cleavage surfaces, which is large compared to linearly interpolated values of polar AlN and InN (0001) surfaces.