Passivating the sulfur vacancy in monolayer MoS2

Haichang Lu,John Robertson,Andrew Kummel

doi:10.1063/1.5030737

Haichang Lu, John Robertson + Show 1 more

Open Access

https://doi.org/10.1063/1.5030737

Copy DOI

Abstract

Various methods to passivate the sulfur vacancy in 2D MoS2 are modeled using density functional theory (DFT) to understand the passivation mechanism at an atomic scale. First, the organic super acid, bis(trifluoromethane)sulfonimide (TFSI) is a strong protonating agent, and it is experimentally found to greatly increase the photoluminescence efficiency. DFT simulations find that the effectiveness of passivation depends critically on the charge state and number of hydrogens donated by TFSI since this determines the symmetry of the defect complex. A symmetrical complex is formed by three hydrogen atoms bonding to the defect in a −1 charge state, and this gives no bandgap states and a Fermi level in the midgap. However, a charge state of +1 gives a lower symmetry complex with one state in the gap. One or two hydrogens also give complexes with gap states. Second, passivation by O2 can provide partial passivation by forming a bridge bond across the S vacancy, but it leaves a defect state in the lower bandgap. On the other hand, substitutional additions do not shift the vacancy states out of the gap.

Highlights

In 3D semiconductors, there are strategies available to passivate defects
We study various possible passivation schemes for transition metal dichalcogenides (TMDs) and explain why they are more complicated than for simpler covalent semiconductors like Si
(1) MoS2 defect states can be removed by charge transfer doping via the van der Waals bonding of an organic monolayer, titanyl phthalocyanine (TiOPC).[15] (2) Thiol-based molecules can reduce the sulfur vacancy density on MoS2 and aAuthor to whom correspondence should be addressed: jr@eng.cam.ac.uk

Summary

Introduction

In 3D semiconductors, there are strategies available to passivate defects. In MoS2, ways to passivate defects have been tried with varying success, but there is presently no general understanding of how best to achieve this. Passivating the sulfur vacancy in monolayer MoS2 (1) MoS2 defect states can be removed by charge transfer doping via the van der Waals bonding of an organic monolayer, titanyl phthalocyanine (TiOPC).[15] (2) Thiol-based molecules can reduce the sulfur vacancy density on MoS2 and aAuthor to whom correspondence should be addressed: jr@eng.cam.ac.uk

Results

Conclusion