Identifying suitable substrates for high-quality graphene-based heterostructures

TL;DR

This study uses Raman spectroscopy to evaluate how different substrates affect the strain and doping in high-quality CVD graphene heterostructures, emphasizing substrate flatness as crucial for device quality.

Contribution

It introduces a contamination-free transfer method and systematically assesses substrate effects on graphene quality using Raman spectroscopy.

Findings

Substrate flatness is critical for high-quality graphene.

Raman spectra reveal doping and strain variations due to substrates.

High-quality heterostructures are achieved with low doping and strain.

Abstract

We report on a scanning confocal Raman spectroscopy study investigating the strain-uniformity and the overall strain and doping of high-quality chemical vapour deposited (CVD) graphene-based heterostuctures on a large number of different substrate materials, including hexagonal boron nitride (hBN), transition metal dichalcogenides, silicon, different oxides and nitrides, as well as polymers. By applying a hBN-assisted, contamination free, dry transfer process for CVD graphene, high-quality heterostructures with low doping densities and low strain variations are assembled. The Raman spectra of these pristine heterostructures are sensitive to substrate-induced doping and strain variations and are thus used to probe the suitability of the substrate material for potential high-quality graphene devices. We find that the flatness of the substrate material is a key figure for gaining, or preserving high-quality graphene.