Unveiling the Defect Structure of Localized Excitons in WSe₂ Monolayer

Understanding and controlling defects in crystalline materials is an everlasting theme in material science and engineering. For two dimensional materials at atomic limit, defects are more influential and have come to the forefront in the pursuit of electronic and optoelectronic applications. In particular, intrinsic defects in semiconducting transition metal dichalcogenide (TMD) monolayers lower the carrier mobility and photoluminescence quantum yield despite of their direct semiconducting bandgap. Furthermore, defects in WSe₂ monolayer host localized excitons that could behave as single quantum emitters (SQEs) at low temperature. However, the exact nature of these defects remains elusive. In this talk, I will introduce our recent progress in study of the point defect in WSe₂ by using low temperature scanning tunneling microscopy and spectroscopy, in corroboration with density functional theory calculations. We observed the tungsten vacancy is the dominant defect in WSe₂ and can form localized exciton. In the end of the talk, I will also discuss the relationship between the localized exciton trapped by the tungsten vacancy and the SQEs. We conjecture that the tungsten vacancy defect is a likely candidate, at least a precursor, for SQEs in the WSe₂ monolayer.