Electronic structure of (Ga, Mn) As revisited

The detailed nature of electronic states mediating ferromagnetic coupling in dilute magnetic semiconductors, specifically (Ga, Mn) As, has been an issue of long debate. Two confronting models have been discussed emphasizing host band versus impurity band carriers. Using angle resolved photoemission we show that the electronic structure of the (Ga, Mn) As system is significantly modified from that of GaAs throughout the valence band. Close to the Fermi energy, the presence of Mninduces a strong mixing of the bulk bands of GaAs, which results in the appearance of a highly dispersive band in the gap region of GaAs. ForMnconcentrations above1% the band reaches the Fermi level, and can thus host the delocalized holes needed for ferromagnetic coupling. Overall, our data provide a firm evidence of delocalized carriers belonging to the modified host valence band.