Valence-band discontinuity between GaN and AlN measured by x-ray photoemission spectroscopy

The valence-band discontinuity at a wurtzite GaN/AlN(0001) heterojunction is measured by x-ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence-band maximum in both GaN and AlN bulk films. The precise location of the valence-band maximum is determined by aligning prominent features in the valence-band spectrum with calculated densities of states. Tables of core level binding energies relative to the valence-band maximum are reported for both GaN and AlN. Subsequent measurements of separations between Ga and Al core levels for thin overlayers of GaN film grown on AlN and vice versa yield a valence-band discontinuity of ΔE_V=0.8±0.3 eV in the standard type I heterojunction alignment.