Electronic and magnetic properties of Ga_1-xMn_xAs: Role of Mn defect bands

Ga_1-xMn_xAs and related semiconductors are under intense investigation for the purpose of understanding the ferromagnetism in these materials, pursuing higher T_C, and, finally, for realizing semiconductor electronic devices that use both charge and spin. In this work, the electronic and magnetic structures of Ga_1-xMn_xAs (x = 3.125%, 6.25%, 12.5%, 25.0%, 50.0%) are studied by first-principles full-potential linearized augmented plane wave calculations with the generalized-gradient approximation. The ferromagnetic state is lower in energy than the paramagnetic and antiferromagnetic states. It is confirmed that Mn atoms stay magnetic with well localized magnetic moments. The calculated band structure shows that Mn doping also forms defect bands, and makes (Ga,Mn)As p-type conducting by providing holes. Furthermore, an s-d population inversion is found in the Mn electronic configuration, which results from the strong Mn p-d mixing. The induced As moments are substantial (about - 0.15μ_B per Mn atom, and almost independent of x) - in accord with a recent observed negative As magnetic circular dichroism signal.