Intrinsic valence band study of molecular-beam-epitaxy-grown GaAs and GaN by high-resolution hard X-ray photoemission spectroscopy

The electronic structures of molecular beam epitaxy (MBE)-grown GaAs and GaN have been studied by means of a technique using a newly developed surface-insensitive probe, namely, high-resolution hard X-ray (HX) synchrotron radiation (hv = 5.95 keV) photoemission spectroscopy (PES). The obtained valence band spectra and shallow core electronic states are compared with those calculated by the full-potential local density approximation (LDA) calculations explicitly including the Ga 3d core state. The experimental valence band spectra show a very good match with the calculations, simulated with linear combinations of the partial density of states. The Ga 3d core on d core states in GaN indicates a set of fine structures which are attributed to the Ga 3d-N 2s hybridization effect. The present experiments indicate that HX-PES provides an indispensable probe for investigating valence band electronic structures of materials, which has so far been impossible due to the limitations of proper surface preparation methods.