Oxygen-Driven Growth Regulation and Defect Passivation in Chemical Vapor Deposited MoS₂ Monolayers

Abstract

Due to the lowest formation energies, sulfur vacancies are inevitable in the vapor-phase chemical vapor deposition (CVD) of MoS2, which act as deep donors and induce midgap defect states, making the material intrinsically n-type. The postgrowth oxygen passivation of such defects has been the subject of a large number of recent studies because passivation of defects augments the photoluminescence quantum yield by several orders. In this study, by introducing an SiO2/Si wafer in close proximity to the growth substrate, we were able to supply trace oxygen in situ during the growth while simultaneously enabling chemisorption of oxygen at defect sites on the basal plane of large-area MoS2 monolayers. Low-temperature photoluminescence spectroscopy allowed us to distinguish clearly the nature of oxygen bonding in defective MoS2 grown with and without the trace oxygen. Chemisorption of oxygen enabled elimination of defect-related bound exciton emission at the near band edge transition of MoS2, leading to about 300% enhancement in the photoluminescence. We observed unusual splitting of the first-order A1g Raman mode in monolayer MoS2 films when the sulfur vacancies are not compensated by oxygen. The present study provides new experimental evidence to better distinguish between chemisorption and physisorption of oxygen and may serve as an effective way to tune the optical properties of van der Waals crystals during the large-area CVD process.

Vertical MoS2 Nanosheets via Space-Confined CVD for Room Temperature Photo-Enhanced Highly Selective Triethylamine Sensing

“…This finding serves as strong evidence for the formation of MoS 2 , without the occurrence of any intermediate phases. Additionally, Figure f shows the O 1s peak at 532.1 eV, most likely originating from the edge defect of the Mo–O peak . The XPS results agree well with the Raman spectroscopy and TEM observations, thus further strengthening the conclusions.…”

Real-Time Investigation of Sulfur Vacancy Generation and Passivation in Monolayer Molybdenum Disulfide via in situ X-ray Photoelectron Spectromicroscopy

“…Following in situ oxygen exposure, we observe a significant (∼5×) increase of PL intensity (Figure 5h), which has also been observed for annealing and oxygen plasma treatments of defects in MoS 2 . 59,73,74 Combined with the observed decrease of SVrelated states at the VB edge, the increasing radiative recombination efficiency following in situ oxygen exposure indicates that oxygen is an effective electronic passivant for SVs.…”

“…However, it is apparent that the dominant impact of irradiation is to reduce the emission intensity, indicating a significant increase of the nonradiative recombination rate with increasing SV concentrations. Following in situ oxygen exposure, we observe a significant (∼5×) increase of PL intensity (Figure h), which has also been observed for annealing and oxygen plasma treatments of defects in MoS 2 . ,, Combined with the observed decrease of SV-related states at the VB edge, the increasing radiative recombination efficiency following in situ oxygen exposure indicates that oxygen is an effective electronic passivant for SVs.…”

2D Rhenium Dichalcogenides: From Fundamental Properties to Recent Advances in Photodetector Technology

“…While intrinsic defects can be manifold, [285] chalcogen vacancies in ReX 2 remain as the most common and prevailing defects, similar to the well-established case of MoS 2 . [228,268,286,287] Moreover, due to their low forming energy, sulfur vacancy defects can be highly mobile in ReS 2 , and hence under the application of an electric field, their motion can be used to modulate the Schottky barrier height at the metal contact region. [288] The presence of trap states within the bandgap provides ReS 2 photodetectors with significant photoconductive gain enhancement and much faster temporal response.…”