Determination of polar C‐plane and nonpolar A‐plane AlN/GaN heterojunction band offsets by X‐ray photoelectron spectroscopy

We have directly measured the valence-band offsets (VBOs) of wurtzite C-plane and A-plane AlN/GaN heterojunctions by X-ray photoelectron spectroscopy. The VBOs were determined to be 0.82 +/- 0.15 and 0.63 +/- 0.15eV for the C-plane and A-plane AlN/GaN heterojunctions, respectively. The discrepancy in VBOs of heterojunctions with different orientations is mainly due to the spontaneous polarization effect. The VBO of the nonpolar heterojunction is closer to the intrinsic value since the A-plane samples show no polarization effects.