X-ray photoelectron spectroscopy and theory of the valence band and semicore Ga 3d states in GaN.

Abstract

The effects of the Ga 3d semicore levels on the electronic structure of GaN are discussed. While band-structure theory using the local-density approximation predicts these states to overlap with the N 2s band and to have important effects on the total energy, x-ray photoelectron spectroscopy (XPS) shows that they occur \ensuremath{\sim}3 eV below the N 2s band. This apparent discrepancy is resolved by means of a so-called \ensuremath{\Delta} SCF or difference of self-consistent-fields calculation, in which the binding energy is calculated as a total-energy difference including solid state screening effects by means of the excited-atom model. The calculated valence-band densities of states are found to be in good agreement with the XPS spectrum. The differences between zinc blende and wurtzite GaN are discussed.