Contact Engineering High-Performance n-Type MoTe₂ Transistors

Abstract

Semiconducting MoTe2 is one of the few two-dimensional (2D) materials with a moderate band gap, similar to silicon. However, this material remains underexplored for 2D electronics due to ambient instability and predominantly p-type Fermi level pinning at contacts. Here, we demonstrate unipolar n-type MoTe2 transistors with the highest performance to date, including high saturation current (>400 µA/µm at 80 K and >200 µA/µm at 300 K) and relatively low contact resistance (1.2 to 2 kΩ•µm from 80 to 300 K), achieved with Ag contacts and AlOx encapsulation. We also investigate other contact metals, extracting their Schottky barrier heights using an analytic subthreshold model. High-resolution X-ray photoelectron spectroscopy reveals that interfacial metal-Te compounds dominate the contact resistance. Among the metals studied, Sc has the lowest work function but is the most reactive, which we counter by inserting monolayer h-BN between MoTe2 and Sc. These metal-insulator-semiconductor (MIS) contacts partly de-pin the metal Fermi level and lead to the smallest Schottky barrier for electron injection. Overall, this work improves our understanding of n-type contacts to 2D materials, an important advance for low-power electronics.

A versatile photodetector assisted by photovoltaic and bolometric effects

“…Figure 2a shows a schematic of our heterostructure. A thick MoTe 2 flake is chosen to fabricate a heterostructure with VO 2 because it always behaves as an n-type material 35 and its bandgap is relatively narrow compared to other TMDCs 16 . Figure 2b shows an optical image of the fabricated heterostructure.…”

Complementary Type Ferroelectric Memory Transistor Circuits with P‐ and N‐Channel MoTe2

“…Until recent years, 2D semiconductors including such a variety of transition metal dichalcogenides (TMDs) or single elements have been extensively studied due to their excellent physical n-channel from the homogeneous thin MoTe 2 . [8,[34][35][36] MoTe 2 shows somewhat ambipolar behavior [34,37,38] depending on its thickness. A few nm-thin MoTe 2 shows p-type while it becomes n-type when doped with H atoms [35,36] or gets thick to a few tens nm (i.e., the comparably small energy gap (≈0.95 eV) of a few nm-thin layer becomes even smaller with the thickness (0.88 eV for bulk)).…”

“…We deliberately select a few nm‐thin p‐MoTe 2 among many other 2D semiconductors in considering such complementary structure, because p‐type MoTe 2 ‐based ferroelectric memory is not reported yet, and also because it is relatively easy to obtain both p‐ and n‐channel from the homogeneous thin MoTe 2 . [ 8,34–36 ] MoTe 2 shows somewhat ambipolar behavior [ 34,37,38 ] depending on its thickness. A few nm‐thin MoTe 2 shows p‐type while it becomes n‐type when doped with H atoms [ 35,36 ] or gets thick to a few tens nm (i.e., the comparably small energy gap (≈0.95 eV) of a few nm‐thin layer becomes even smaller with the thickness (0.88 eV for bulk)).…”

Correlating the electronic structures of metallic/semiconducting MoTe2 interface to its atomic structures

“…Two-dimensional (2D) transition metal dichalcogenides (TMDs) have attracted extensive attention for their potential applications in nanoelectronics [ 1 , 2 ]. In atomically thin TMD devices, contact interface properties can significantly influence the performance, particularly in short-channel devices [ 3 , 4 ]. An imperfect interface between the electrode and a 2D semiconducting TMD can cause Fermi level pinning and thus result in high resistance across the contact [ 2 , 5 ], which limits potential applications as device sizes scale down.…”

“…An imperfect interface between the electrode and a 2D semiconducting TMD can cause Fermi level pinning and thus result in high resistance across the contact [ 2 , 5 ], which limits potential applications as device sizes scale down. Recent strategies such as indium/gold contacts [ 6 ], tunneling contacts [ 7 ], and metallic 2D material contacts [ 8 ] have been used to reduce contact resistance in long-channel devices [ 3 , 6–9 ]. However, these techniques are less effective in short-channel devices or large-scale applications.…”