Determination of N-polar AlN/GaN heterojunction valance-band offsets by X-ray photoelectron spectroscopy

The N-polar AlN/GaN heterojunctions were grown by metal organic chemical vapor deposition on planar and vicinal sapphire substrates. The valence-band offsets (VBOs) were directly determined to be 2.18 ± 0.15 eV and 2.05 ± 0.15 eV for N-polar AlN/GaN heterojunctions grown on planar and vicinal sapphire substrates by X-ray photoelectron spectroscopy measurement, respectively.