Reducing self-compensating Mn interstitials in (Ga, Mn)As via nanostructure engineering

A consistent increase in Curie temperature (Tc) with decreasing (Ga, Mn)As wire width was observed in the experiment by Chen et al (2011 Nano Lett. 11 2584). In this paper, we calculate the formation energy of Mn interstitials located at different sites in a nanostructure with different shapes, orientations, surface atoms and sizes. We find that when the Mn atom is located at the outmost tetrahedral interstitial site and the As atoms occupy this tetrahedral outside surface, the formation energy is the smallest regardless of the shape and orientation, but it increases with reducing size of the nanowire. Therefore, increasing the free surface by nanostructure engineering allows the Mn interstitials to diffuse out at the sidewalls. Reducing the self-compensating Mn interstitials will effectively increase the Tc of a (Ga, Mn)As magnetic semiconductor, which gives a good explanation to the previous experimental observation. (paper)