Electronic structure of1×1GaN(0001) andGaN(0001¯)surfaces

Abstract

The electronic structure of clean and Ga- or N-covered $1\ifmmode\times\else\texttimes\fi{}1$ GaN(0001) and $\mathrm{GaN}(0001\ifmmode\bar\else\textasciimacron\fi{})$ surfaces is studied using the local-density approximation of density-functional theory employing ab initio pseudopotentials together with Gaussian orbital basis sets. We use both standard and self-interaction- and relaxation-corrected pseudopotentials. The latter allow for a most accurate description of the electronic structure of these surfaces. Comparing the formation energies for the clean and adatom-covered $1\ifmmode\times\else\texttimes\fi{}1$ configurations, we determine optimal surface structures for various growth conditions. For the GaN(0001) surface in the Ga-rich case, we find a structural model consisting of Ga adatoms adsorbed in ${T}_{4}$ positions above the substrate surface to be most favorable. In the N-rich case, the clean GaN(0001) surface is the most stable $1\ifmmode\times\else\texttimes\fi{}1$ configuration. For the $\mathrm{GaN}(0001\ifmmode\bar\else\textasciimacron\fi{})$ surface, our results for both Ga- and N-rich growth conditions indicate that a full monolayer of Ga adatoms adsorbed in on top positions is the most stable configuration. Our theoretical results allow for a comparison of full calculations of the surface electronic structure for a number of optimized structural models with most recent angle-resolved photoemission spectroscopy data.