VALENCE-BAND DISCONTINUITY BETWEEN GAN AND ALN MEASURED BY X-RAY PHOTOEMISSION SPECTROSCOPY

The valence-band discontinuity at a wurtzite GaN/AlN(0001) heterojunct ion is measured by x-ray photoemission spectroscopy. The method first measures the core level binding energies with respect to the valence-b and maximum in both GaN and AlN bulk films. The precise location of th e 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 a re reported for both GaN and AlN. Subsequent measurements of separatio ns between Ga and Al core levels for thin overlayers of GaN film grown on AlN and vice versa yield a valence-band discontinuity of DELTAE(V) =0.8+/-0.3 eV in the standard type I heterojunction alignment.