Metal Semiconductor interface

Abstract

Molybdenum disulfide (MoS2) nanosheet, one of two-dimensional (2D) semiconductors, has recently been regarded as a promising material to break through the limit of present semiconductors. With an apparent energy band gap, it certainly provides a high carrier mobility, superior subthreshold swing, and ON/OFF ratio in field-effect transistors (FETs). However, its potential in carrier mobility has still been depreciated since the field-effect mobilities have only been measured from metal–insulator–semiconductor (MIS) FETs, where the transport behavior of conducting carriers located at the insulator/MoS2 interface is unavoidably interfered by the interface traps and gate voltage. Moreover, thin MoS2 MISFETs have always shown large hysteresis with unpredictable negative threshold voltages. Here, we for the first time report MoS2-based metal semiconductor field-effect transistors (MESFETs) using NiO Schottky electrode which makes van der Waals interface with MoS2. We thus expect that the maximum mobilities or carrier transport behavior of the Schottky devices may hardly be interfered by interface traps or an on-state gate field. Our MESFETs with a few and ∼10 layer MoS2 demonstrate intrinsic-like high mobilities of 500–1200 cm2/(V s) at a certain low threshold voltage between −1 and −2 V without much hysteresis. Moreover, they work as a high speed and highly sensitive phototransistor with 2 ms switching and ∼5000 A/W, respectively, supporting their high intrinsic mobility results.

Optical images of several MoS2 nanosheets which play as the channel of MESFET, schematic energy ban diagram, schematic illustrations for MESFET operations, comparison between NiO and pure metal contact for MESFET, transconductance plots of 10-layer MoS2 MESFET, Padovani–Stratton parameter for electron density estimation, reproducibility of MESFET, AFM profile and Raman spectra obtained from 4-layer MoS2, OLED operation using our MESFET. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsnano.5b02785.