Transition from Hopping to Band-like Transport in Weakly Coupled Multilayer MoS₂ Field Effect Transistors

Abstract

In this article, multilayer MoS 2 manufactured from a multiple-transfer process of chemical vapor deposition (CVD)-grown monolayer MoS 2 is studied. Because of the lattice mismatch and larger distance between adjacent MoS 2 layers, the interlayer interaction is weakened and the band structure transition from direct to indirect as well as band gap shrinkage effect in multilayer is suppressed, as indicated by Raman and photoluminescence spectra. These structural differences from that of the exfoliated MoS 2 make stacked MoS 2 layers a better configuration for fabricating high-performance MoS 2 field effect transistor (FET). Here, back-gate MoS 2 FETs with different number of layers were fabricated. As the number of layers increases from 1 to 3, the devices' mobility and on/off ratio show an enhancement from 2 to 62 cm 2 /s•V and 10 6 to 10 8 , respectively. Metal-to-insulator transition (MIT) phenomena are also observed in bilayer MoS 2 FET. A distributed resistance-based model is proposed to study the conductivity of weakly coupled MoS 2 layers. Combining the resistance model with temperature dependence characteristics, it is demonstrated that the electron mobility in monolayer MoS 2 is limited by the hopping transport mechanism, whereas the electron in the bilayer can be excited to band-like transport mode because of the immunity of the influence from the charge traps at the substrate, which explains the enhancement of mobility and MIT phenomena. This study is universally valid for other twodimensional materials, paving way to fabricate high-performance nanoelectronics for integrated circuits.

Transfer-Free Growth of Bi2O2Se on Silicon Dioxide via Chemical Vapor Deposition

“…A heavily doped 300 nm p-type silicon substrate was used for back-gate Bi 2 O 2 Se FET. , The device was fabricated using electron beam lithography for device structure, followed by metal deposition of drain and source electrodes with e-beam evaporation (Figure a). The device was annealed after the lift-off process under the argon pressure of 300 Torr for 1 h to improve the quality of the contact (Figure b). , The rectangular shape of the sample (length ∼ 56 μm; width ∼ 38 μm) was observed after depositing metal electrodes (Figure b).…”

Manipulation of the electrical and memory properties of MoS2 field-effect transistors by highly charged ion irradiation

“…For 2D TMDCs it has already been shown, that an increase in chalcogen vacancies or interface defects can lead to hopping transport via localized states and, as a consequence, lead to an increasing conductivity. 58,75 Nevertheless, temperature-dependent conductivity measurements would be needed to conrm a change in the transport mechanism due to the irradiation. 76,77 Note, that the FET irradiated with 200 ions/mm 2 is the only exception to the otherwise linear behavior.…”

Single‐Gate In‐Transistor Readout of Current Superposition and Collapse Utilizing Quantum Tunneling and Ferroelectric Switching

“…This transition differs from the conventional transitions observed in hopping-to-band-like transport or charge localization-to-delocalization, which display similar crossing points but only reveal insulating behavior of I D at decreasing V G and lower carrier densities. [72][73][74] Furthermore, it is not a percolation-type transition that occurs when charge domains enlarge and become interconnected. [75] We attribute this observed transition to up/down ferroelectric polarization switching.…”