Gate-controlled spin filter, spin valve, and negative differential resistance in cold metal/bipolar magnetic semiconductor lateral homologous heterojunctions

Achieving multifunctional integration in two dimensions is highly desired for developing next-generation nanoelectronic devices but remains a challenge. Here, combining the advantages of cold metal and a bipolar magnetic semiconductor (BMS), three distinct functions, i.e., a spin filter, spin valve, and negative differential resistance, are simultaneously realized in a cold metal 2H-TaS₂/BMS2H-VS₂/cold metal 2H-TaS₂ lateral homologous heterojunction, where the BMS 2H-VS₂ is controlled by two electric gates placed on the left and right parts. The spin filter and spin valve effects originate from the bipolar spin-polarized band structure of 2H-VS₂, where its carriers' spin orientation can be easily flipped by shifting the Fermi level into either the valence or conduction band. Thus, in the junction, the current's spin polarization (spin up or spin down) and intensity (high or low conductance) can be switched by adjusting the polarities of the two applied gates: Once two gate voltages are both positive or negative, the junction works as a spin filter with either a fully spin-down or fully spin-up polarized current. While the two gate voltages possess opposite signs, the junction's current is prohibited due to mismatched spin orientations of carriers in the two parts of 2H-VS₂, leading to the spin valve effect. At the same time, the intrinsic energy gaps around the Fermi level in cold metal 2H-TaS₂ and the band-to-band tunneling of carriers from 2H-TaS₂ to 2H-VS₂ endow the junction with a significant negative differential resistance behavior with a large peak-to-valley current ratio.