Localized defect states in MoS$_2$ monolayers: electronic and optical properties

TL;DR

This study investigates how point and line defects affect the electronic and optical properties of MoS2 monolayers, revealing localized defect states and their minimal impact on optical absorption at low defect concentrations.

Contribution

It provides a detailed analysis of defect-induced electronic states and optical effects in MoS2 monolayers using density-functional methods, highlighting the robustness of the electronic structure.

Findings

Defect states are localized and form deep or shallow levels in the band gap.

Point defect concentration up to 6% does not significantly alter electronic structure.

Higher defect concentrations affect optical absorption, with vacancies quenching absorption and sulfur defects creating new peaks.

Abstract

Defects usually play an important role in tuning and modifying various properties of semiconducting or insulating materials. Therefore we study the impact of point and line defects on the electronic structure and optical properties of MoS2 monolayers using density-functional methods. The different types of defects form electronic states that are spatially localized on the defect. The strongly localized nature is reflected in weak electronic interactions between individual point or line defect and a weak dependence of the defect formation energy on the defect concentration or line defect separation. In the electronic energy spectrum the defect states occur as deep levels in the band gap, as shallow levels very close to the band edges, as well as levels in-between the bulk states. Due to their strongly localized nature, all states of point defects are sharply peaked in energy. Periodic line defects form nearly dispersionless one-dimensional band structures and the related spectral features are also strongly peaked. The electronic structure of the monolayer system is quite robust and it is well preserved for point defect concentrations of up to 6%. The impact of point defects on the optical absorption for concentrations of 1% and below is found to be very small. For higher defect concentrations molybdenum vacancies were found to quench the overall absorption and sulfur defects lead to sharp absorption peaks below the absorption edge of the ideal monolayer. For line defects, we did not find a considerable impact on the absorption spectrum. These results support recent experiments on defective transition metal chalcogenides.