Theoretical investigation of the GaN (0001) surface reconstruction

Using density functional theory we study the surface reconstruction of GaN (0001). We compare energetics of the 2x2 and root 3 by root 3 R30 GaN (0001) surface structures and find them to be energetically equivalent. In addition, we systematically compare the results found when using the local density approximation and the generalized gradient approximation. We also consider Ga and La ad-atoms on Ga (0001), and determine the corresponding potential energy surfaces and diffusion rates and compare them with those previously computed for Eu, Ce, and Gd. In addition, similarly to the cases of Eu, Ce, and Gd, the La ad-atom exchange with a surface Ga atom is found energetically favorable and with a much smaller barrier of 0.15 eV. This may indicate a path to forming intermetallic LaGa₂ through the surface exchange reaction.