Localized defect states in MoS₂monolayers: Electronic and optical properties

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 MoS 2 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.

Impact of the MoS2 Starting Material on the Dispersion Quality and Quantity after Liquid Phase Exfoliation

“…Note that we made a similar observation for the dispersions resulting from the shorter sonication time (Supplementary Figures 21–23). As mentioned above, optical properties such as PL can be influenced by defect states. − The Mo:S ratio of the bulk materials of SA2 and SAnp were determined to be 1.92 ± 0.00 and 2.11 ± 0.00 by EDX, respectively (Supplementary Table 7). The standard deviation is statistical and results from measurements of multiple spots.…”

Electronic and optical properties of vacancy defects in single-layer transition metal dichalcogenides

“…Point defects in SL TMDCs have been explored both theoretically and experimentally. [13][14][15][16][17][18] Recent photoluminescence (PL) experiments [16][17][18] reveal that localized excitonic states related to VDs can serve as singlephoton emitters in WSe 2 . Magnetism in low dimensional systems is another area of interest.…”

Anomalous electrical transport in orientationally controlled trinary hybrids of graphene and twisted bilayer molybdenum disulphide

“…Due to disorder-induced chargepuddle formation in graphene around the Dirac point, we were not able to observe these anomalies. Other factors include localization at the band tail of MoS 2 (due to defect states in MoS 2 ) [28] and formation of a mobility edge [29] that prevents gate-voltage screening by the flatbands of MoS 2 that lie near the MoS 2 conduction band edge. Thus, even though flatbands are present, we are not able to resolve them experimentally.…”