Electric and Magnetic Field Tunable Rectification and Magnetoresistance in Fe_xGe_1−x/Ge Heterojunction Diodes

Fe_xGe_1−x/Ge amorphous heterojunction diodes with p-Fe_xGe_1−x ferromagnetic semiconductor layers are grown on single-crystal Ge substrates of p-type, n-type and intrinsic semiconductors, respectively. The I–V curves of p−Fe_0.4Ge_0.6/p−Ge diodes only show slight changes with temperature or with magnetic field. For the p-Fe_0.4Ge_0.6/n−Ge diode, good rectification is maintained at room temperature. More interestingly, the I–V curve of the p−Fe_0.4Ge_0.6/i-Ge diode can be tuned by the magnetic field, indicating a large positive magnetoresistance. The resistances of the junctions decrease with the increasing temperature, suggesting a typical semiconductor transport behavior. The origin of the positive magnetoresistance is discussed based on the effect of the electric and magnetic field on the energy band structures of the interface.