Spectroscopic studies of atomic defects and bandgap renormalization in semiconducting monolayer transition metal dichalcogenides

TL;DR

This study uses spectroscopy and theoretical calculations to identify atomic defect states and analyze bandgap renormalization in monolayer transition metal dichalcogenides, revealing defect origins and many-body interaction effects.

Contribution

It spectroscopically locates chalcogen vacancies in four monolayer SC TMDs and analyzes their effects on electronic properties with combined experimental and theoretical methods.

Findings

Midgap states from chalcogen vacancies identified in four TMDs

Many-body interactions significantly increase quasiparticle gaps and excitonic binding energies

Atomic defect origins differ among the studied TMDs

Abstract

Assessing atomic defect states and their ramifications on the electronic properties of two dimensional van der Waals semiconducting transition metal dichalcogenides (SC TMDs) is the primary task to expedite multi disciplinary efforts in the promotion of next generation electrical and optical device applications utilizing these low dimensional materials. Here, with electron tunneling and optical spectroscopy measurements with density functional theory, we spectroscopically locate the midgap states from chalcogen atom vacancies in four representative monolayer SC TMDs (MoS2, WS2, MoSe2, WSe2), and carefully analyze the similarities and dissimilarities of the atomic defects in four distinctive materials regarding the physical origins of the missing chalcogen atoms and the implications to SC mTMD properties. In addition, we address both quasiparticle and optical energy gaps of the SC mTMD films and find out many body interactions significantly enlarge the quasiparticle energy gaps and excitonic binding energies, when the semiconducting monolayers are encapsulated by non interacting hexagonal boron nitride layers.