Photoluminescence Enhancement and Structure Repairing of Monolayer MoSe₂by Hydrohalic Acid Treatment

Abstract

Atomically thin two-dimensional transition-metal dichalcogenides (TMDCs) have attracted much attention recently due to their unique electronic and optical properties for future optoelectronic devices. The chemical vapor deposition (CVD) method is able to generate TMDCs layers with a scalable size and a controllable thickness. However, the TMDC monolayers grown by CVD may incorporate structural defects, and it is fundamentally important to understand the relation between photoluminescence and structural defects. In this report, point defects (Se vacancies) and oxidized Se defects in CVD-grown MoSe2 monolayers are identified by transmission electron microscopy and X-ray photoelectron spectroscopy. These defects can significantly trap free charge carriers and localize excitons, leading to the smearing of free band-to-band exciton emission. Here, we report that the simple hydrohalic acid treatment (such as HBr) is able to efficiently suppress the trap-state emission and promote the neutral exciton and trion emission in defective MoSe2 monolayers through the p-doping process, where the overall photoluminescence intensity at room temperature can be enhanced by a factor of 30. We show that HBr treatment is able to activate distinctive trion and free exciton emissions even from highly defective MoSe2 layers. Our results suggest that the HBr treatment not only reduces the n-doping in MoSe2 but also reduces the structural defects. The results provide further insights of the control and tailoring the exciton emission from CVD-grown monolayer TMDCs.

Optoelectronic Devices Based on Atomically Thin Transition Metal Dichalcogenides

“…Very recently, however, solution-based chemical treatment of MoS 2 by an organic superacid [12] has resulted in a quantum yield of more than 95%. Similar improvements were reported by chemical treatments of other TMDs [13]. These studies open the door for the development of more efficient TMD-based light emitters and other optoelectronic devices.…”

Repairing atomic vacancies in single-layer MoSe2 field-effect transistor and its defect dynamics

“…23,24,29 For the SLM FET, such defects lead to various carrier mobilities, 19,24,[30][31][32][33] and defect repairing is the focus of concern during these years. 17,28,34,35 Here we report that a simple drop of chemical solution may repair the defect-rich SLM FET, by which the carrier mobility increases from 0.1 to around 30 cm 2 /Vs. The aberration-corrected high resolution transmission electron microscopy (HRTEM), Raman scattering, and density functional theory (DFT) calculations reveal the defect dynamics for the Selenium (Se) vacancy repair, which suggests the localization source of the transport carriers.…”

“…This is consistent with the picture in literature. 17 The defect repair dynamics from the first-principles calculations The DFT calculations complete the Se vacancy repair scenario. The model is a supercell consisting of 4 × 4 SLM unit cells with a single Fig.…”

“…13 Among them, research attention on MoSe 2 is rising because of its high photo-responsivity and tunable excitonic charges. 5,[14][15][16][17] It best matches the solar spectrum with its bandgap of 1.5 eV. This leads to the potential applications in optoelectronic devices, such as single-junction solar cells 18 and photoelectrochemical devices, based on single-layer MoSe 2 (SLM) with a direct bandgap and an even higher optical coupling strength.…”

Exciton radiative lifetime in transition metal dichalcogenide monolayers

“…It has been shown recently that the latter process (Auger type) is dominant at room temperature 53,54 .…”