Coexistence of room-temperature negative differential resistance and unsaturated magnetoresistance effects in germanium-based devices

We demonstrate room-temperature negative differential resistance (NDR) and unsaturated magnetoresistance (MR) effects in germanium-based devices. Our findings indicate that the observed NDR primarily originates from the carrier injection effect induced by local impact ionization in germanium. As the magnetic field increases, the MR values exhibit an unsaturated behavior, increasing quadratically at low fields and transitioning to a linear increase at higher fields, reaching approximately 91% at 1 T. We attribute this large unsaturated MR to carrier inhomogeneity. The equivalent Hall electric field strength was used to characterize the degree of carrier inhomogeneity under magnetic fields: a larger equivalent Hall electric field strength indicates stronger carrier inhomogeneity and consequently a larger corresponding MR. The coexistence of excellent room-temperature NDR and large unsaturated MR in germanium-based devices (achieved by constructing electrodes at two edge positions on the semiconductor surface) enables the development of multifunctional devices.