Abstract
AbstractAtomically thin layers of van der Waals (vdW) crystals offer an ideal material platform to realize tunnel field‐effect transistors (TFETs) that exploit the tunneling of charge carriers across the forbidden gap of a vdW heterojunction. This type of device requires a precise energy band alignment of the different layers of the junction to optimize the tunnel current. Among 2D vdW materials, black phosphorus (BP) and indium selenide (InSe) have a Brillouin zone‐centered conduction and valence bands, and a type II band offset, both ideally suited for band‐to‐band tunneling. TFETs based on BP/InSe heterojunctions with diverse electrical transport characteristics are demonstrated: forward rectifying, Zener tunneling, and backward rectifying characteristics are realized in BP/InSe junctions with different thickness of the BP layer or by electrostatic gating of the junction. Electrostatic gating yields a large on/off current ratio of up to 108 and negative differential resistance at low applied voltages (V ≈ 0.2 V). These findings illustrate versatile functionalities of TFETs based on BP and InSe, offering opportunities for applications of these 2D materials beyond the device architectures reported in the current literature.
Highlights
We report on tunnel-field effect transistors (FETs) (TFETs) based on a black phosphorus (BP)/indium selenide (InSe) heterostructure contacted with graphene electrodes and capped with a hBN layer acting as an effective encapsulating layer and dielectric for electrostatic gating
We demonstrate the operation of these tunnel field effect transistors (TFETs) at low applied voltages (< 0.5 V) and a diverse range of electrical characteristics controlled by the field effect, including negative differential resistance (NDR) due to interlayer band-to-band tunneling (BTBT)
We have demonstrated band-to-band tunneling in BP/InSe heterostructures by using a dual-gate device architecture
Summary
The progressive miniaturization of electronic devices has propelled several technologies to higher performance and efficiency, but further progress and innovative solutions to global challenges require a shift from traditional approaches towards transformative material systems and integration technologies.[1,2] Atomically thin layers of van der Waals (vdW) crystals and their heterostructures,[35] generally referred to as two-dimensional (2D) materials, offer opportunities to study and exploit quantum phenomena for a wide range of applications.[6,7,8,9,10] These crystals have strong covalent atomic bonding in the 2D planes and weak vdW interaction between the layers, which enable the fabrication of stable thin films down to the atomic monolayer thickness and stack them into multi-layered heterostructures.[11,12,13] The science of these 2D systems is developing rapidly with important technological breakthroughs emerging from recent studies. Of particular interest is the opportunity to exploit tunneling across this heterojunction as BP and InSe present a number of attractive features: they both have a Brillouin zonecentered conduction band (CB) and exhibit a type II band offset,[31,32,33] which are well suited to control and exploit the transmission of charge carriers between different bands of the heterostructure for the realization of a tunnel-FET (TFET) This type of device concept has been demonstrated using junctions based on graphene and other 2D materials,[7,35] including WSe2/SnSe2 heterojunctions[36] and tunnel diodes based on MoS2/WSe2 with a symmetric dual-gate architecture.[37] for many 2D materials, such as TMDCs, the band edges are located at the K-point of the Brillouin zone. The transition between these diverse functionalities can be achieved in a single device through a dual gate modulation approach
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