Deterministic direct growth of WS2 on CVD graphene arrays

TL;DR

This paper demonstrates a scalable, direct chemical vapor deposition method to grow monolayer WS2 exclusively on graphene arrays on SiO2, creating heterostructures with potential for electronic and optoelectronic applications.

Contribution

It introduces a novel, deterministic growth technique for WS2 on graphene arrays, enabling controlled heterostructure fabrication on common substrates.

Findings

WS2 grows only on graphene crystals, forming a vertical heterostack.

Graphene experiences compressive strain and hole doping after WS2 growth.

Heterostructure acts as an electron-blocking layer at positive gate voltages.

Abstract

The combination of the exciting properties of graphene with those of monolayer tungsten disulfide (WS2) makes this heterostack of great interest for electronic, optoelectronic and spintronic applications. The scalable synthesis of graphene/WS2 heterostructures on technologically attractive substrates like SiO2 would greatly facilitate the implementation of novel two-dimensional (2D) devices. In this work, we report the direct growth of monolayer WS2 via chemical vapor deposition (CVD) on single-crystal graphene arrays on SiO2. Remarkably, spectroscopic and microscopic characterization reveals that WS2 grows only on top of the graphene crystals so that the vertical heterostack is selectively obtained in a bottom-up fashion. Spectroscopic characterization indicates that, after WS2 synthesis, graphene undergoes compressive strain and hole doping. Tailored experiments show that such hole doping is caused by the modification of the SiO2 stoichiometry at the graphene/SiO2 interface during the WS2 growth. Electrical transport measurements reveal that the heterostructure behaves like an electron-blocking layer at large positive gate voltage, which makes it a suitable candidate for the development of unipolar optoelectronic components.