Indirect bandgap of hBN-encapsulated monolayer MoS2

TL;DR

This study shows that encapsulating monolayer MoS2 with hBN changes its fundamental electronic properties from direct to indirect bandgap, affecting its optical behavior.

Contribution

It provides experimental and theoretical evidence that hBN encapsulation alters the band structure of monolayer MoS2, revealing a transition from direct to indirect bandgap.

Findings

Temperature dependence of photoluminescence differs from SiO2 substrate case.

Ab-initio calculations show orbital hybridization causes bandgap change.

hBN encapsulation impacts intrinsic properties of 2D materials.

Abstract

We present measurements of temperature dependence of photoluminescence intensity from monolayer MoS2 encapsulated by hexagonal boron nitride (hBN) flakes. The obtained temperature dependence shows an opposite trend to that of previously observed in a monolayer MoS2 on a SiO2 substrate. Ab-initio bandstructure calculations have revealed that monolayer MoS2 encapsulated by hBN flakes have no longer a direct-gap semiconductor but an indirect-gap semiconductor. This is caused by orbital hybridization between MoS2 and hBN, which leads to upward shift of gamma-valley of MoS2. This work shows an important implication that the hBN-encapsulated structures used to address intrinsic properties of two-dimensional crystals can alter basic properties encapsulated materials.