Intrinsic hole localization mechanism in magnetic semiconductors

The interplay between clustering and exchange coupling in magnetic semiconductors for the prototype (Ga1-xMnx)As is investigated considering manganese concentrations x of 1/16 and 1/32, which are in the interesting experimental range. For x similar to 6%, we study all possible arrangements of two Mn atoms on the Ga sublattice within a large supercell and find the clustering of Mn atoms at nearest-neighbour Ga sites energetically preferred. As shown by analysis of spin density and projected density of states, this minimum-energy configuration localizes further one hole and reduces the effective charge carrier concentration. Also the exchange coupling constant increases to a value corresponding to lower Mn concentrations with decreasing inter-Mn distance.