Interlayer coupling and gate-tunable excitons in transition metal dichalcogenide heterostructures

TL;DR

This paper uses first-principles calculations to study how interlayer coupling affects excitonic properties in transition metal dichalcogenide heterostructures, revealing their tunability via external electric fields for optoelectronic applications.

Contribution

It provides a detailed first-principles analysis of interlayer excitons and introduces a simple model to predict their gate-tunable properties in 2D heterostructures.

Findings

Interlayer coupling significantly influences excitonic properties.

Gate fields can tune exciton energy, oscillator strength, and lifetime.

A simple model captures the physics of exciton tunability.

Abstract

Bilayer van der Waals (vdW) heterostructures such as MoS2/WS2 and MoSe2/WSe2 have attracted much attention recently, particularly because of their type II band alignments and the formation of interlayer exciton as the lowest-energy excitonic state. In this work, we calculate the electronic and optical properties of such heterostructures with the first-principles GW+Bethe-Salpeter Equation (BSE) method and reveal the important role of interlayer coupling in deciding the excited-state properties, including the band alignment and excitonic properties. Our calculation shows that due to the interlayer coupling, the low energy excitons can be widely tunable by a vertical gate field. In particular, the dipole oscillator strength and radiative lifetime of the lowest energy exciton in these bilayer heterostructures is varied by over an order of magnitude within a practical external gate field. We also build a simple model that captures the essential physics behind this tunability and allows the extension of the ab initio results to a large range of electric fields. Our work clarifies the physical picture of interlayer excitons in bilayer vdW heterostructures and predicts a wide range of gate-tunable excited-state properties of 2D optoelectronic devices.