Theoretical study of GaN (0001) surface reconstructions and La and Ga ad-atoms under N- and Ga-rich conditions

We use density functional theory (DFT) to study the surface reconstruction of GaN (0001). We compare the surface reconstructions between the 2x2 GaN(0001) and (√3x√3)R30 GaN(0001) surface simulation cells and find that both are energetically equivalent but the electronic structure for each reconstruction differs at the surface. We also determine the potential energy surface and diffusion rates of Ga and La on (√3x√3)R30 GaN(0001) and (2√3x2√3)R30 GaN(0001) and compare them with the diffusion rates of Eu, Ce, and Gd. The exchange of a La and Ga ad-atom with a surface Ga atom is also studied and we determine that an exchange between a surface Ga atom and the La ad-atom is energetically favorable, while an exchange between a surface Ga atom and the Ga ad-atom is not.