Spatial Structure of Mn-Mn Acceptor Pairs in GaAs

Abstract

The local density of states of Mn-Mn pairs in GaAs is mapped with cross-sectional scanning tunnelingmicroscopy and compared with theoretical calculations based on envelope-function and tight-bindingmodels. These measurements and calculations show that the crosslike shape of the Mn-acceptor wavefunction in GaAs persists even at very short Mn-Mn spatial separations. The resilience of the Mn-acceptorwave function to high doping levels suggests that ferromagnetism in GaMnAs is strongly influenced byimpurity-band formation. The envelope-function and tight-binding models predict similarly anisotropicoverlaps of the Mn wave functions for Mn-Mn pairs. This anisotropy implies differing Curie temperaturesfor Mn -doped layers grown on differently oriented substrate