Ab-initio studies of the Sc adsorption and the ScN thin film formation on the GaN(000-1)-(2 × 2) surface

• Studies of the initial stages in the formation of Sc and ScN structures on GaN
• In the adsorption of Sc on the GaN the Br site is the most favorable geometry.
• When a Sc replaces a Ga of the first monolayer the displaced Ga occupies a T4-2 site.
• For Ga-rich conditions there is formation of ScN under the Ga monolayer.
• In N-rich conditions there is formation of ScN in the wurtzite phase.

First principles total energy calculations have been performed to investigate the initial stages of the Sc adsorption and ScN thin film formation on the GaN(000-1)-(2 × 2) surface. Studies are done within the periodic density functional theory as implemented in the PWscf code of the Quantum ESPRESSO package. The Sc adsorption at high symmetry sites results in the bridge site as the most stable structure. When a Sc monolayer is deposited above the surface the T4 site results as the most stable geometry. The Sc migration into the first Ga monolayer induces the Ga displaced ad-atom to be adsorbed at the T4-2 site. A ScN bilayer may be obtained under the Ga monolayer. Finally a ScN bilayer may be formed in the wurtzite phase above the surface. The formation energy plots show that in the moderate Ga-rich conditions we obtain the formation of a ScN bilayer under the gallium monolayer. However at N-rich conditions the formation of ScN bilayer above the surface is the most favorable structure. We report the density of states to explain the electronic structure of the most favorable geometries.