Surface and bulk electronic structure of thin-film wurtzite GaN

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 $\Gamma \Delta A,\hspace{0.5em}\Gamma \Sigma M$, and $\Gamma \mathrm{TK}$ 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)-(1×1). 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.