First-principles theoretical analysis and electron energy loss spectroscopy of vacancy defects in bulk and nonpolar (10(1)over-bar0) surface of GaN

We determine atomic structure, electronic structure, formation energies, magnetic properties of native point defects, such as gallium (Ga) and nitrogen (N) vacancies, in bulk and at the nonpolar (10 (1) over bar0) surface of wurtzite gallium nitride (w-GaN) using first-principles density functional theory (DFT) based calculations. In bulk and at the (10 (1) over bar0) surface of GaN, N vacancies are significantly more stable than Ga vacancies under both Ga-rich and N-rich conditions. We show that within DFT-local density approximated N vacancies form spontaneously at the (10 (1) over bar0) surface of GaN when doped to raise the Fermi level up to approximate to 1.0 eV above valence band maximum (VBM) while with valence band edge correction it is 1.79 eV above VBM. We provide experimental evidence for occurrence of N vacancies with electron energy loss spectroscopy measurements, which further hints the N vacancies at surface to the source of auto-doping which may explain high electrical conductivity of GaN nanowall network grown with molecular beam epitaxy. Published under license by AVS.