Anomalous optical response of graphene on hexagonal boron nitride substrates

TL;DR

This paper investigates the unique optical properties of graphene on hexagonal boron nitride substrates, revealing enhanced absorption and overcoming measurement challenges through advanced spectroscopic techniques.

Contribution

It introduces a novel imaging spectroscopic ellipsometry method to determine the optical constants of graphene on hBN, addressing the anisotropic dielectric tensor challenge.

Findings

Graphene on hBN shows about 60% higher absorption than on SiO2/Si.

The study successfully retrieves optical constants of graphene in 250-950 nm range.

Enhanced optical response of graphene on hBN compared to standard substrates.

Abstract

Graphene/hBN heterostructures can be considered as one of the basic building blocks for the next-generation optoelectronics mostly owing to the record-high electron mobilities. However, currently, the studies of the intrinsic optical properties of graphene are limited to the standard substrates (SiO2/Si, glass, quartz) despite the growing interest in graphene/hBN heterostructures. This can be attributed to a challenging task of the determination of hBN's strongly anisotropic dielectric tensor in the total optical response. In this study, we overcome this issue through imaging spectroscopic ellipsometry utilizing simultaneous analysis of hBN's optical response with and without graphene monolayers. Our technique allowed us to retrieve the optical constants of graphene from graphene/hBN heterostructures in a broad spectral range of 250-950 nm. Our results suggest that graphene's absorption on hBN may exceed the one of graphene on SiO2/Si by about 60 %.