Influence of the density of states of graphene on the transport properties of graphene/MoS2/metal vertical field-effect transistors

TL;DR

This study investigates how the low density of states in graphene affects the electrical transport in graphene/MoS2/metal vertical transistors, revealing Fermi level shifts and enabling Dirac point spectroscopy through I-V measurements.

Contribution

It demonstrates a method to perform Dirac point spectroscopy and determine MoS2 capacitance using simple DC transport measurements in graphene-based heterostructures.

Findings

Fermi level shifts with bias voltage in graphene/MoS2/metal transistors

Nonlinear I-V characteristics at the Dirac point

Capacitance of MoS2 layer measured via transport data

Abstract

We performed detailed studies of the current-voltage characteristics in graphene/MoS2/metal vertical field-effect transistors. Owing to its low density of states, the Fermi level in graphene is very sensitive to its carrier density and thus the external electric field. Under the application of a bias voltage VB between graphene and the metal layer in the graphene/MoS2/metal heterostructure for driving current through the van der Waals interface, the electric field across the MoS2 dielectric induces a shift in the Fermi level of graphene. When the Fermi level of graphene coincides with the Dirac point, a significant nonlinearity appears in the measured I-V curve, thus enabling us to perform spectroscopy of the Dirac point. By detecting the Dirac point for different back-gate voltages, we revealed that the capacitance of the nanometer-thick MoS2 layer can be determined from a simple DC transport measurement.