P-Type Ohmic Contact to Monolayer WSe₂ Field-Effect Transistors Using High-Electron Affinity Amorphous MoO₃

Abstract

Monolayer tungsten diselenide (1L-WSe2) has been widely used for studying emergent physics due to the unique properties of its valence bands. However, electrical transport studies have been impeded by the lack of a reliable method to realize Ohmic hole-conducting contacts to 1L-WSe2 especially at low carrier densities and low temperatures. Here, we report low-temperature p-type Ohmic contact to 1L-WSe2 field-effect transistors at carrier densities (n) below n = 1 × 1012 cm–2 with negligible temperature dependence down to the lowest measured temperature (10 K). The non-rectifying barrier is achieved between 1L-WSe2 and molybdenum trioxide (MoO3), where 1L-WSe2 underneath MoO3 is heavily hole-doped through surface transfer doping. Electrical transport measurements reveal linear current–voltage relations at a temperature of 10 K and carrier densities from n = 7.7 × 1011 cm–2 to below the threshold. The finding is also supported by nearly temperature-independent output curves up to room temperature and a negligible contact barrier down to the subthreshold regime. Furthermore, the contact resistivity of MoO3-contacted 1L-WSe2 FET is 30.2–64.8 kΩ μm at n = 1.5 × 1012 cm–2, which is the lowest reported for 1L-WSe2 FETs at such low carrier density. Realizing robust p-type Ohmic contact to a 2D transition metal dichalcogenide semiconductor will enable direct electronic measurements of quantum transport in correlated phases in the valence bands of monolayer semiconductors.

Memory Window Ratio Enhancement of p-Type WSe2 Memtransistors Using Dielectric GeSe2 Nanosheets with Asymmetric Interfaces for Neuromorphic Computing

“…A charge-trapping hysteresis mechanism is illustrated in Figure a for the WSe 2 /Janus-GeSe 2 device, where voltage pulses are applied to the bottom gate to modulate the working state. Previous reports have demonstrated that the ionization potential and bandgap of few-layer WSe 2 are 4.8–5.2 eV , and 1.2 eV, whereas the electron affinity and wide bandgap of multilayer GeSe 2 are 3.3 and 2.7 eV . The WSe 2 /GeSe 2 vdWH forms a type I band alignment (Figure b).…”

Tapping the Performance of a Tungsten Disulfide Field-Effect Transistor with Deep Structure Optimization and Theoretical Simulation

“…The electrical properties of the WS 2 -FETs were tested using a probe station. The obtained output and transfer characteristic curves, I d – V d and I d – V g , were nonlinear, indicating that a Schottky contact had been formed by a mismatch in the work function between the WS 2 nanosheet and the metal electrode. − The carrier mobility of the WS 2 -FETs is calculated using the carrier mobility equation, as follows: μ FE = L C W V normald ∂ I ∂ V normalg where L is the device channel length, W is the channel width, C is the capacitance per unit area of the SiO 2 dielectric layer (the capacitance C per unit area of 300 nm SiO 2 is 11.5 nF·cm –2 , and the value of capacitance per unit area is inversely proportional to thickness). V d is the drain voltage, and ∂ I /(∂ V g ) is the value of the slope of the tangent line on the transfer curve.…”

Reliable Memristive Synapses Based on Parylene-MoOx Nanocomposites for Neuromorphic Applications

“…Additional stabilization of copper filaments likely occurs due to the spatial limitation of ion migration by molybdenum oxide. Moreover, copper near molybdenum oxide is expected to lose electrons, given that the work function from a copper crystal is about ∼4.5 eV, and the Fermi level of MoO 3 is estimated to be as low as −6.9 eV (even for amorphous and nonstoichiometric oxides, the levels are similarly low) with a conductance band slightly above it . Consequently, the filament is encircled by two layers of spatial charge: positive on the copper surface and negative on the adjacent molybdenum oxide.…”

“…Moreover, copper near molybdenum oxide is expected to lose electrons, given that the work function from a copper crystal is about ∼4.5 eV, and the Fermi level of MoO 3 is estimated to be as low as −6.9 eV (even for amorphous and nonstoichiometric oxides, the levels are similarly low) with a conductance band slightly above it. 57 Consequently, the filament is encircled by two layers of spatial charge: positive on the copper surface and negative on the adjacent molybdenum oxide. A sufficiently strong electric field is generated within this layer, attracting copper ions away from the surface, thereby reducing the activation energy of the surface diffusion.…”