Percolative switching in transition metal dichalcogenide field-effect transistors at room temperature

TL;DR

This study reveals that the switching mechanism in TMDC FETs at room temperature is a classical percolation transition, characterized by noise measurements indicating inhomogeneous carrier density and a crossover from resistor network to continuum percolation.

Contribution

It provides a microscopic understanding of the switching in TMDC FETs through noise analysis, establishing percolation as the fundamental transport mechanism at room temperature.

Findings

Switching in TMDC FETs is a classical percolation transition.

Noise scaling reveals signatures of percolation in resistor networks.

The transition crosses over to continuum percolation at higher doping levels.

Abstract

We have addressed the microscopic transport mechanism at the switching or on-off transition in transition metal dichalcogenide (TMDC) field-effect transistors (FET), which has been a controversial topic in TMDC electronics, especially at room temperature. With simultaneous measurement of channel conductivity and its slow time-dependent fluctuation (or noise) in ultra-thin WSe2 and MoS2 FETs on insulating SiO2 substrates, where noise arises from McWhorter-type carrier number fluctuations, we establish that the switching in conventional backgated TMDC FETs is a classical percolation transition in a medium of inhomogeneous carrier density distribution. From the experimentally observed exponents in the scaling of noise magnitude with conductivity, we observe unambiguous signatures of percolation in random resistor network, particularly in WSe2 FETs close to switching, which crosses over to continuum percolation at a higher doping level. We demonstrate a powerful experimental probe to the microscopic nature of near-threshold electrical transport in TMDC FETs, irrespective of the material detail, device geometry or carrier mobility, which can be extended to other classes of 2D material-based devices as well.