Magneto-optical spectra and the presence of an impurity band in p-type ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature

Abstract

By using magnetic circular dichroism (MCD) spectroscopy with photon energy in both visible (1.5-5 eV) and infrared light regions (0.6-1.7 eV), we systematically investigate the band structure of p-type ferromagnetic semiconductor (Ga 1-x ,Fe x )Sb with various Fe concentrations x = 2%-20% grown by low-temperature molecular beam epitaxy. We observed two peaks in the infrared MCD spectra that can be explained by the optical transitions related to the Fermi level (E F ) located in an Fe-related impurity band (IB) in the bandgap. As x increases, the energy shifts of the two peaks suggest that the Fe-related IB extends into the bandgap and E F rises correspondingly. Furthermore, the mobility of hole carriers in these (Ga,Fe)Sb thin films estimated by Hall measurements is very low (0.2-2 cm 2 /Vs), which is consistent with our conclusion that the hole carriers and E F reside in the IB rather than in the valence band. Our results provide insights into the band structure of p-type ferromagnetic semiconductors (Ga,Fe)Sb with high Curie temperature, which is promising for the realization of spintronic devices operating at room temperature.