Structural and magnetic properties of Mn-doped GaAs(1 1 0) surface

We have investigated STM images of the (1 1 0) cross-sectional surface of Mn-doped GaAs using first principles total-energy pseudopotential calculations. We focus on configurations with Mn interstitial in the uppermost surface layers. In particular, we have found that Mn impurities, surrounded by Ga or As atoms, introduce in both cases strong local distortions in the GaAs(1 1 0) surface, with bond length variations up to 8% on surface and non-negligible relaxations effects propagating up to the third subsurface layer. In both cases interstitial Mn induces a spin-polarization on its nearest neighbors, giving rise to a ferromagnetic Mn-As and to antiferromagnetic Mn-Ga configuration.