Formation of Mn-derived impurity band in III-Mn-V alloys by valence band anticrossing

While the support for the existence of a Mn-derived impurity band in the diluted magnetic semiconductor Ga_1-x Mn_x As has recently increased, a detailed quantitative analysis of its formation and properties is still incomplete. Here, we show that such an impurity band arises as the result of an anticrossing interaction between the extended states of the GaAs valence band and the strongly localized Mn states according to the valence band anticrossing model. The anticrossing interpretation is substantiated by optical measurements that reveal a shift in the band gap of GaAs upon the addition of Mn and it also explains the remarkably low hole mobility in this alloy. Furthermore, the presence of a Mn-derived impurity band correctly accounts for the metal-to-insulator transition experimentally observed in Ga_1-xMn_xAs_1-y(N,P)_y with y≤0.02. © 2008 The American Physical Society.