title: Defect-Tolerant Monolayer Transition Metal Dichalcogenides.
abstract: Localized electronic states formed inside the band gap of a semiconductor due to crystal defects can be detrimental to the material's optoelectronic properties. Semiconductors with a lower tendency to form defect induced deep gap states are termed defect-tolerant. Here we provide a systematic first-principles investigation of defect tolerance in 29 monolayer transition metal dichalcogenides (TMDs) of interest for nanoscale optoelectronics. We find that the TMDs based on group VI and X metals form deep gap states upon creation of a chalcogen (S, Se, Te) vacancy, while the TMDs based on group IV metals form only shallow defect levels and are thus predicted to be defect-tolerant. Interestingly, all the defect sensitive TMDs have valence and conduction bands with a very similar orbital composition. This indicates a bonding/antibonding nature of the gap, which in turn suggests that dangling bonds will fall inside the gap. These ideas are made quantitative by introducing a descriptor that measures the degree of similarity of the conduction and valence band manifolds. Finally, the study is generalized to nonpolar nanoribbons of the TMDs where we find that only the defect sensitive materials form edge states within the band gap.
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Mohnish
authors.initials: M
authors.lastname: Pandey
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Filip A
authors.initials: FA
authors.lastname: Rasmussen
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Korina
authors.initials: K
authors.lastname: Kuhar
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Thomas
authors.initials: T
authors.lastname: Olsen
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Karsten W
authors.initials: KW
authors.lastname: Jacobsen
authors.affiliation: Center for Atomic-Scale Materials Design (CAMD), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.|Center for Nanostructured Graphene (CNG), Department of Physics, Technical University of Denmark , DK-2800 Kongens Lyngby, Denmark.
authors.forename: Kristian S
authors.initials: KS
authors.lastname: Thygesen
mesh_terms: D055664:Electrochemical Techniques; D028561:Transition Elements / Q000737:chemistry*
chemical_list: D028561:Transition Elements
keywords: 2D materials; Defect tolerance; density functional theory; descriptor; fingerprint; nanoribbon