Two-dimensional transitional metal dichalcogenide (TMD) field-effect transistors (FETs) are promising candidates for future electronic applications, owing to their excellent transport properties and potential for ultimate device scaling. However, it is widely acknowledged that substantial contact resistance associated with the contact-TMD interface has impeded device performance to a large extent. It has been discovered that O2 plasma treatment can convert WSe2 into WO3-x and substantially improve contact resistances of p-type WSe2 devices by strong doping induced thinner depletion width. In this paper, we carefully study the temperature dependence of this conversion, demonstrating an oxidation process with a precise monolayer control at room temperature and multilayer conversion at elevated temperatures. Furthermore, the lateral oxidation of WSe2 under the contact revealed by HR-STEM leads to potential unpinning of the metal Fermi level and Schottky barrier lowering, resulting in lower contact resistances. The p-doping effect is attributed to the high electron affinity of the formed WO3-x layer on top of the remaining WSe2 channel, and the doping level is found to be 2 dependent on the WO3-x thickness that is controlled by the temperature. Comprehensive materials and electrical characterizations are presented, with a low contact resistance of ~528  m and record high on-state current of 320 A/m at -1V bias being reported.

The valley degree of freedom of electrons in two-dimensional transition metal dichalcogenides has been extensively studied by theory (1–4), optical (5–9), and optoelectronic (10–13) experiments. However, generation and detection of pure valley current without relying on optical selection have not yet been demonstrated in these materials. Here, we report that valley current can be electrically induced and detected through the valley Hall effect and inverse valley Hall effect, respectively, in monolayer molybdenum disulfide. We compare temperature and channel length dependence of nonlocal electrical signals in monolayer and multilayer samples to distinguish the valley Hall effect from classical ohmic contributions. Notably, valley transport is observed over a distance of 4 μm in monolayer samples at room temperature. Our findings will enable a new generation of electronic devices using the valley degree of freedom, which can be used for future novel valleytronic applications.

Schottky barrier (SB) transistors operate distinctly different from conventional metal‐oxide semiconductor field‐effect transistors, in a unique way that the gate impacts the carrier injection from the metal source/drain contacts into the channel region. While it has been long recognized that this can have severe implications for device characteristics in the subthreshold region, impacts of contact gating of SB in the on‐state of the devices, which affects evaluation of intrinsic channel properties, have been yet comprehensively studied. Due to the fact that contact resistance (RC) is always gate‐dependent in a typical back‐gated device structure, the traditional approach of deriving field‐effect mobility from the maximum transconductance (gm) is in principle not correct and can even overestimate the mobility. In addition, an exhibition of two different threshold voltages for the channel and the contact region leads to another layer of complexity in determining the true carrier concentration calculated from Q = COX * (VG–VTH). Through a detailed experimental analysis, the effect of different effective oxide thicknesses, distinct SB heights, and doping‐induced reductions in the SB width are carefully evaluated to gain a better understanding of their impact on important device metrics.

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Spin Orbit Torque Magnetic RAM (SOT-MRAM) is emerging as a promising memory technology owing to its high endurance, reliability and speed. A critical factor for its success is the development of materials that exhibit efficient conversion of charge current to spin current, characterized by their spin Hall efficiency. In this work, it is experimentally demonstrated that the spin Hall efficiency of the industrially relevant ultra-thin Ta can be enhanced by more than 25× when a monolayer (ML) WSe 2 is inserted as an underlayer. The enhancement is attributed to spin absorption at the Ta/WSe 2 interface, suggested by harmonic Hall measurements. The presented hybrid spin Hall stack with a 2D WSe 2 underlayer has a total body thickness of less than 2 nm and exhibits greatly enhanced spin Hall efficiency, which makes this hybrid a promising candidate for energy efficient SOT-MRAM.