Electronic transport in graphene-based heterostructures

TL;DR

This study compares the surface morphology and electronic transport properties of graphene on various 2D crystal substrates, revealing that WS2 and MoS2 support high mobility, but GaSe degrades quickly, affecting device stability.

Contribution

It provides a comparative analysis of different 2D crystal substrates for graphene, highlighting their effects on electronic mobility and stability, which was previously unclear.

Findings

Graphene on BN exhibits high mobility (~38,000 cm2/Vs)

Graphene on WS2 and MoS2 also shows promising high mobility

GaSe substrates degrade over time, causing hysteresis in transport measurements

Abstract

While boron nitride (BN) substrates have been utilized to achieve high electronic mobilities in graphene field effect transistors, it is unclear how other layered two dimensional (2D) crystals influence the electronic performance of graphene. In this letter, we study the surface morphology of 2D BN, gallium selenide (GaSe) and transition metal dichalcogenides (tungsten disulfide (WS2) and molybdenum disulfide (MoS2)) crystals and their influence on graphene's electronic quality. Atomic force microscopy analysis show that these crystals have improved surface roughness (root mean square (rms) value of only ~ 0.1 nm) compared to conventional SiO2 substrate. While our results confirm that graphene devices exhibit very high electronic mobility on BN substrates, graphene devices on WS2 substrates (G/WS2) are equally promising for high quality electronic transport (~ 38,000 cm2/Vs at RT), followed by G/MoS2 (~ 10,000 cm2/Vs) and G/GaSe (~ 2,200 cm2/Vs). However, we observe a significant asymmetry in electron and hole conduction in G/WS2 and G/MoS2 heterostructures, most likely due to the presence of sulphur vacancies in the substrate crystals. GaSe crystals are observed to degrade over time even under ambient conditions, leading to a large hysteresis in graphene transport making it a less suitable substrate.