nl5b04513_si_002.pdf (20.28 MB)
Defect-Tolerant Monolayer Transition Metal Dichalcogenides
journal contribution
posted on 2016-03-30, 00:00 authored by Mohnish Pandey, Filip A. Rasmussen, Korina Kuhar, Thomas Olsen, Karsten W. Jacobsen, Kristian S. ThygesenLocalized 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.