NbS₂ Monolayers as Bipolar Magnetic Semiconductors for Multifunctional Spin Diodes and 3 nm Cold-Source Spin Field-Effect Transistors

To mitigate the increase in static and dynamic power dissipation due to the short-channel effect, several field-effect transistors (FETs) have been designed and investigated, among which cold-source FETs based on cold-source metals with a special band structure can effectively reduce the power dissipation by lowering the subthreshold swing (SS) to break the Boltzmann limit of 60 mV/dec. In this paper, we find that the bipolar magnetic semiconductors, such as monolayer 2H-NbS2 (ML-NbS2), can be modulated as "cold" metals with half-metallic properties by appropriate doping. We then design two types of nanodevices based on ML-NbS2 and theoretically study their spin-resolved transport properties. The results show that the ML-NbS2 diode has an on/off ratio of up to 106 and a perfect spin filtering effect. Instructively, the 3 nm p-type ML-NbS2 cold-source spin FET exhibits not only a spin filtering effect but also a negative differential resistance effect at zero gate voltage. By introduction of the high-κ dielectric, ultrahigh Ion = 5747 μA/μm and ultralow steepest subthreshold swing SS = 59 mV/dec can be achieved at a supply voltage of 0.64 V. In addition, the optimized 3 nm ML-NbS2 FET meets the high-performance requirements of the International Technology Roadmap for Semiconductors at different supply voltages. These results provide a pathway for the development of multifunctional low-power spintronic devices.