Evolution of Fe 3d impurity band state as the origin of high Curie temperature in the p-type ferromagnetic semiconductor (Ga,Fe)Sb

[Formula: see the attached file] is one of the promising ferromagnetic semiconductors for spintronic device applications because its Curie temperature (Tc) is above 300 K when the Fe concentration x is equal to or higher than similar to ∼0.20. However, the origin of the high Tc in (Ga,Fe)Sb remains to be elucidated. To address this issue, we use resonant photoemission spectroscopy (RPES) and first-principles calculations to investigate the x dependence of the Fe 3d states in [Formula: see text] (x = 0.05, 0.15, and 0.25) thin films. The observed Fe 2p-3d RPES spectra reveal that the Fe-3d impurity band (IB) crossing the Fermi level becomes broader with increasing x, which is qualitatively consistent with the picture of double-exchange interaction. Comparison between the obtained Fe-3d partial density of states and the first-principles calculations suggests that the Fe-3d IB originates from the minority-spin (↓) e states. The results indicate that enhancement of the double-exchange interaction between e↓ electrons with increasing x is the origin of the high Tc in (Ga,Fe)Sb.