Polarity inversion of GaN(0 0 0 1) surfaces induced by Si adsorption

We employ density-functional theory within the local-density approximation to study the structural and electronic properties of Si monolayers adsorbed at GaN(0 0 0 1) surfaces. We find that when the N atoms reside in the outermost layer of the surface, the (0 0 0 1) surface converts into a (0001¯) surface, giving rise to a polarity inversion. We explain this inversion as a charge compensation effect between the N dangling bonds states at the outermost surface layer and the Si donor state in the subsurface layer.