Charge carrier localization in monolayer WS2 influenced by hBN microbubbles

Abstract

The energy landscapes of two-dimensional heterostructures are strongly localized by interfacial defects, which often introduce unique characteristics that can be exploited for advanced nanodevice applications. This study investigates how hBN microbubbles affect the optical and electronic properties of hBN-encapsulated monolayer WS2 using spatially resolved photoluminescence and Raman spectroscopy. Photoluminescence spectral analysis reveals a significant increase in electron density in monolayer WS2 within the region where hBN microbubbles form above WS2. The increased electron density in WS2 is attributed to the flexoelectric effect of the deformed hBN layer. Additionally, the WS2 monolayer exhibited reduced tensile strain in the bubble region compared to the fully encapsulated area, leading to an increase in exciton energy. Raman analysis, which correlates the frequencies of the in-plane and out-of-plane optical phonons in WS2, confirms the changes in strain and electron density observed in the photoluminescence results, highlighting excellent agreement between the two techniques. These findings provide valuable insights into the interplay of strain and charge doping in tuning the electronic properties of monolayer WS2 and emphasize the pivotal role of the flexoelectric effect in modulating charge doping in two-dimensional heterostructures.