Tunable and sizable band gap of single-layer graphene sandwiched between hexagonal boron nitride

Ruge Quhe,Wai-Ning Mei,Jing Lu,Shigeru Nagase,Rui Qin,Guangfu Luo,Zhengxiang Gao,Qihang Liu,Dapeng Yu,Jing Zhou,Jiaxin Zheng

doi:10.1038/am.2012.10

Abstract

Opening a tunable and sizable band gap in single-layer graphene (SLG) without degrading its structural integrity and carrier mobility is a significant challenge. Using density functional theory calculations, we show that the band gap of SLG can be opened to 0.16 eV (without an electric field) and 0.34 eV (with a strong electric field) when properly sandwiched between two hexagonal boron nitride single layers. The zero-field band gaps are increased by more than 50% when the many-body effects are included. The ab initio quantum transport simulation of a dual-gated field effect transistor (FET) made of such a sandwich structure reveals an electric-field-enhanced transport gap, and the on/off current ratio is increased by a factor of 8.0 compared with that of a pure SLG FET. The tunable and sizeable band gap and structural integrity render this sandwich structure a promising candidate for high-performance SLG FETs. Jing Lu and co-workers have revealed how to open up a tunable band gap in single-layer graphene, the one-atom-thick honeycomb carbon layer that has sparked much interest both in fundamental physics and in practical applications. Although graphene's excellent mechanical, thermal and electrical properties are very attractive, one major drawback is its lack of ‘band gap’ — the energy gap in the electronic structure of a material that enables to switch its conductivity on and off. Previous attempts to create such a gap in single-layer graphene have typically damaged its structure or conductivity. Through extensive calculations, the researchers have now examined the properties of single-layer graphene when sandwiched between two honeycomb boron nitride (BN) layers. They revealed that for a specific positioning of the layers, a sizable band gap can be opened and further tuned by applying an electric field without causing damage, making the sandwich structure a promising component for field-effect transistors. An electric field-enhanced transport gap is well established in a dual-gated field effect transistor (FET) based on the h-BN/single-layer graphene/h-BN sandwich structure, and the on/off current ratio is increased by a factor of 8.0 compared with pure single-layer graphene FET. The tunable and sizeable band gap and structural integrity render this sandwich structure a promising candidate for high-performance single-layer graphene FETs.

Highlights

Despite its extremely high carrier mobility (1. 5Â104 cm[2] VÀ1 sÀ1 for a SiO2-supported sample[1] and 2Â105 cm[2] VÀ1 sÀ1 for a suspended sample2,3), pristine graphene cannot be used for effective roomtemperature field effect transistors (FET) because of its zero band gap
density functional theory (DFT) electronic structure A supercell is constructed for the sandwich structure of a single layer of graphene that is inserted between two hexagonal boron nitride (h-BN) single layers
The chemical vapor deposition (CVD) process has been used to grow graphene on a metal-substrate-supported h-BN single layer with either a strong[34] or weak[36,37] interaction between the h-BN single layer and the metal substrates and a well-defined orientation with respect to the h-BN layer.[34]

Summary

Introduction

Despite its extremely high carrier mobility (1. 5Â104 cm[2] VÀ1 sÀ1 for a SiO2-supported sample[1] and 2Â105 cm[2] VÀ1 sÀ1 for a suspended sample2,3), pristine graphene cannot be used for effective roomtemperature field effect transistors (FET) because of its zero band gap. The most effective type II method is the application of an external electric field to the graphene Both theoretical calculations and experiments show that a vertical external electric field can induce a tunable band gap of up to 0.25 eV for bilayer graphene (BLG)[11,12,13] because it breaks the inversion symmetry of BLG, and the carrier mobility is not significantly affected by the vertical electric field.[13] The mechanism of opening a BLG band gap by strain[10] is the generation of an equivalent vertical electric field by different strains on two layers. It is highly desirable to develop an effective method to open a tunable and sizable band gap for SLG without significant loss of carrier mobility, as can be done for BLG

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Conclusion