Energetics of H andNH2on GaN(101¯0) and implications for the origin of nanopipe defects

We present first-principles calculations of the formation energy for H-terminated GaN(101¯0) surfaces. The calculations indicate that H adsorption on GaN(101¯0) will proceed by saturation of pairs of Ga and N dangling bonds rather than through exclusive occupation of only one type of bonding site. At $T=0,$ the surface energy of the fully H-terminated surface is found to be 0.02 eV/cell, compared to 1.95 eV/cell for the bare surface. We present results for the N-H and Ga-H stretching and bending eigenfrequencies. Dissociative adsorption of ${\mathrm{NH}}_3$ via the formation of N-H and ${\mathrm{G}\mathrm{a}-\mathrm{N}\mathrm{H}}_2$ bonds is exothermic and reduces the surface formation energy to a value which is less than 0.1 eV at $T=0.\mathrm{}$ The implications of these results for the origin of nanopipe defects in GaN are examined.