Field-Effect Transistors Based on Few-Layered alpha-MoTe_2

TL;DR

This study investigates few-layer alpha-MoTe_2 field-effect transistors, revealing hole doping, mobility comparable to MoS_2 and MoSe_2, and potential for enhanced spin-orbit effects due to tellurium's heavier atomic mass.

Contribution

First comprehensive characterization of alpha-MoTe_2 FETs, including mobility, doping type, and Raman properties, highlighting its potential for spintronic applications.

Findings

Hole-doped FETs with on/off ratios > 10^6

Mobility approaching or exceeding 10 cm^2/Vs

Raman modes show little dependence on layer number

Abstract

Here we report the properties of field-effect transistors based on few layers of chemical vapor transport grown alpha- MoTe_2 crystals mechanically exfoliated onto SiO_2. We performed field-effect and Hall mobility measurements, as well as Raman scattering and transmission electron microscopy. In contrast to both MoS_2 and MoSe_2, our MoTe_2 field-effect transistors (FETs) are observed to be hole-doped, displaying on/off ratios surpassing 106 and typical sub-threshold swings of ~ 140 mV per decade. Both field-effect and Hall mobilities indicate maximum values approaching or surpassing 10 cm^2/Vs which are comparable to figures previously reported for single or bi-layered MoS_2 and/or for MoSe_2 exfoliated onto SiO_2 at room temperature and without the use of dielectric engineering. Raman scattering reveals sharp modes in agreement with previous reports, whose frequencies are found to display little or no dependence on the number of layers. Given that both MoS_2 is electron doped, the stacking of MoTe_2 onto MoS_2 could produce ambipolar field-effect transistors and a gap modulation. Although the overall electronic performance of MoTe_2 is comparable to those of MoS_2 and MoSe_2, the heavier element Te should lead to a stronger spin orbit-coupling and possibly to concomitantly longer decoherence times for exciton valley and spin indexes.