Surface and bulk electronic structure of thin-film wurtzite GaN

Abstract

The bulk and surface valence-band electronic structure of thin-wurtzite GaN has been studied using angle-resolved photoemission spectroscopy. The bulk band dispersion along the $\ensuremath{\Gamma}\ensuremath{\Delta}A, \ensuremath{\Gamma}\ensuremath{\Sigma}M$, and $\ensuremath{\Gamma}\mathrm{TK}$ directions of the bulk Brillouin zone was measured. Our results indicate the local-density approximation band-structure calculations using partial-core corrections for the Ga $3d$ states predict the relative dispersion of many of the observed bands with a high degree of accuracy. Furthermore, a nondispersive feature was identified near the valence-band maximum in a region of $k$ space devoid of bulk states. This feature is identified as emission from a surface state on GaN(0001)-(1\ifmmode\times\else\texttimes\fi{}1). The symmetry of this surface state is even with respect to the mirror planes of the surface and polarization measurements indicate that it is of ${\mathrm{sp}}_{z}$ character, consistent with a dangling-bond state.