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The "direct" spin Hall (DSH) effect has been intensively studied to manipulate the magnetic state in spin–orbit torque magnetic random access memory. Meanwhile, its reciprocal phenomenon, known as the "inverse" spin Hall (ISH) effect, has been studied as a method to read the magnetic state of a magnetic element in a magnetic read head sensor and magnetoelectric spin–orbit logic device. This work studies a magnetic field sensing device structure in which the DSH effect is used for reading the magnetic state in a ferromagnetic (FM)/topological insulator (TI) heterostructure. We found that while the output of our DSH sensing device is consistent with that based on the ISH effect, the spin Hall angle calculated from its magnitude is colossal (θSH ∼ 164) and significantly higher than that (θSH ∼ 3.5) obtained from the second harmonic measurement. Our findings show that the giant DSH and ISH effects in TI-based heterostructures are useful for realizing next-generation magnetic read head device and have important implications for engineering topological quantum materials with high spin Hall performance. [ABSTRACT FROM AUTHOR]

It is technically challenging to shrink the size of a tunneling magnetoresistance reader to below 20 nm for magnetic recording technology beyond 4 Tb/in2 due to its complex film stack. Recently, we proposed a reader architecture based on the inverse spin Hall effect to resolve those challenges, referred below as spin–orbit torque (SOT) reader, whose structure consists of a SOT layer and a ferromagnetic layer. However, the heavy metal-based SOT reader has small output voltage and low signal-to-noise ratio (SNR) due to the limited spin Hall angle θSH (< 1) of heavy metals. In this Letter, we demonstrate the integration of BiSb topological insulator with strong inverse spin Hall effect into the SOT reader that can significantly improve the output voltage and SNR. First, we theoretically calculate the noises in a 20 × 20 nm2 BiSb-based SOT reader to establish the relationships between SNR and θSH at various bias currents. We then demonstrate proof-of-concept BiSb-based SOT readers using CoFe/MgO/BiSb stack, which show large output voltages up to 15 mV at an input current of 9.4 kA/cm2 at room temperature. We project a giant θSH = 61 for BiSb. Our work demonstrates the potential of BiSb for SOT reader beyond 4 Tb/in2 magnetic recording technology. [ABSTRACT FROM AUTHOR]

MoS2 is known to show stubborn n-type behavior due to its intrinsic band structure and Fermi level pinning. Here, we investigate the combined effects of molecular doping and contact engineering on the transport and contact properties of monolayer (ML) MoS2 devices. Significant p-type (hole-transport) behavior was only observed for chemically doped MoS2 devices with high work function palladium (Pd) contacts, while MoS2 devices with low work function metal contacts made from titanium showed ambipolar behavior with electron transport favored even after prolonged p-doping treatment. ML MoS2 transistors with Pd contacts exhibit effective hole mobilities of (2.3 ± 0.7) cm2 V−1 S−1 and an on/off ratio exceeding 106. We also show that p-doping can help to improve electrical contacts in p-type field-effect transistors: relatively low contact resistances of (482 ± 40) kΩ μm and a Schottky barrier height of ≈156 meV were obtained for ML MoS2 transistors. To demonstrate the potential application of 2D-based complementary electronic devices, a MoS2 inverter based on pristine (n-type) and p-doped monolayer MoS2 was fabricated. This work presents a simple and effective route for contact engineering, which enables the exploration and development of high-efficiency 2D-based semiconductor devices. [ABSTRACT FROM AUTHOR]

We report on room-temperature negative transconductance (NTC) in axial Si/Ge hetero-nanowire tunneling field-effect transistors. The NTC produces a current peak-to-valley ratio >45, a high value for a Si-based device. We characterize the NTC over a range of gate VG and drain VD voltages, finding that NTC persists down to VD = --50 mV. The physical mechanism responsible for the NTC is the VG-induced depletion in the p-Ge section that eventually reduces the maximum electric field that triggers the tunneling ID, as confirmed via three-dimensional (3D) technology computer-aided design simulations. [ABSTRACT FROM AUTHOR]