Abstract:
The perturbation of the crystal potential of GaAs due to Mn impurity has three components: a long-range hydrogenic-like potential, common to all acceptors, the central-cell potential (CCP), specific to a given impurity, and spin-dependent hybridization of Mn d-states with neighboring As p-states. Based on tight-binding calculations and comparison of MnGa and ZnGa impurities, we show that neither CCP nor p-d hybridization produces a localized state, at least for realistic strengths of the perturbation. We conclude that the Coulomb potential is crucial for the formation of the MnGa acceptor level at ~0.1eV. Its role weakens in the high-doped ferromagnetic DMS due to screening and overlap of the potential tails. To analyze the transition from a well defined impurity band in the very dilute limit into the disordered valence band in the high doped metallic regime we utilize various tight-binding models adjusted to obtain the MnGa acceptor level without the hydrogenic long-range potential. We show that the impurity band merges merges with the valence band already below 1% of Mn, irrespectively to the details of the perturbation. At about 5% Mn doping, it transforms into a broad feature at the top of the valence band. These results imply that within the microscopic tight-binding description the picture of metal-insulator transition occurring within the impurity band is unrealistic for GaAs doped with Mn.

In collaboration with T. Jungwirth