Gate-modulated conductance of few-layer WSe_2 field-effect transistors in the subgap regime: Schottky barrier transistor and subgap impurity states

Abstract

Two key subjects stand out in the pursuit of semiconductor research: material quality and contact technology. The fledging field of atomically thin transition metal dichalcogenides (TMDCs) faces a number of challenges in both efforts. This work attempts to establish a connection between the two by examining the gate-dependent conductance of few-layer (1-5L) WSe2 field effect devices. Measurements and modeling of the subgap regime reveal Schottky barrier transistor behavior. We show that transmission through the contact barrier is dominated by thermionic field emission (TFE) at room temperature, despite the lack of intentional doping. The TFE process arises due to a large number of subgap impurity states, the presence of which also leads to high mobility edge carrier densities. The density of states of such impurity states is self-consistently determined to be approximately 1-2x10^13 /cm^2/eV in our devices. We demonstrate that substrate is unlikely to be a major source of the impurity states and suspect that lattice defects within the material itself are primarily responsible. Our experiments provide key information to advance the quality and understanding of TMDC materials and electrical devices.

arXiv comment18 pages including SI, 8 figures total

References in corpus (23)

• Boron nitride substrates for high-quality graphene electronics
• Single-Layer MoS2 Phototransistors
• Grains and grain boundaries in highly crystalline monolayer molybdenum disulfide
• Evolution of Electronic Structure in Atomically Thin Sheets of WS2 and WSe2
• High Performance Single Layered WSe2 p-FETs with Chemically Doped Contacts
• Mobility engineering and metal-insulator transition in monolayer MoS2
• Vertical Field Effect Transistor based on Graphene-WS2 Heterostructures for flexible and transparent electronics
• Extraordinary room-temperature photoluminescence in WS2 monolayers
• Carbon Nanotubes as Schottky Barrier Transistors
• Tightly bound excitons in monolayer WSe2
• Two-dimensional transition metal dichalcogenides under electron irradiation: defect production and doping
• Photovoltaic effect in an electrically tunable van der Waals heterojunction
• Quasiparticle band structures and optical properties of strained monolayer MoS2 and WS2
• The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors
• High Mobility Ambipolar MoS2 Field-Effect Transistors: Substrate and Dielectric Effects
• Quantitative Determination of the Band-Gap of WS2 with Ambipolar Ionic Liquid-Gated Transistors
• High Mobility WSe2 p- and n-Type Field Effect Transistors Contacted by Highly Doped Graphene for Low-Resistance Contacts
• Switching Mechanism in Single-Layer Molybdenum Disulfide Transistors: an Insight into Current Flow across Schottky Barriers
• Unconventional Quantum Hall Effect and Tunable Spin Hall Effect in MoS2 Trilayers
• The quantum scattering time and its implications on scattering sources in graphene
• The quantum scattering time and its implications on scattering sources in graphene (Supplementary)
• Diffusive Charge Transport in Graphene on SiO2
• Reduction of Hysteresis for Carbon Nanotube Mobility Measurements Using Pulsed Characterization

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• High Sensitivity Hybrid PbS CQD-TMDC Photodetectors up to 2 $\mu$m
• Screening limited switching performance of multilayer 2D semiconductor FETs: the case for SnS
• Ferroelectric Domain Patterning Controlled Schottky Junction State in Monolayer MoS${}_2$
• Environmental effects on the electrical characteristics of back-gated WSe2 field effect transistors
• Spin transport in n-type single-layer transition metal dichalcogenides