The performance of electrical and optical devices based on two-dimensional semiconductors (2D) such as molybdenum disulfide is critically influenced due to very poor light absorption in the atomically thin layers. In this study, the phonon mediated optical absorption and emission properties in single atomic layers of MoS2 have been investigated. The electronic transitions in MoS2 due to near-field optical interaction and the influence of interface phonons due to the dielectric substrate GaN on the relaxation of optically generated carriers will be described. The near-field interaction can be induced in the presence of metal plasmons deposited on the surface of MoS2 monolayers. A hybrid metal-semiconductor system was realized by the deposition of silver (Ag) NPs on MoS2 layer and the localized plasmon modes were selectively chosen to interact with quasiparticles such as excitons and phonons. These quasiparticles are confined within the single atomic layer of MoS2 and are stable at room temperatures due to high binding energy. The lattice vibrational modes in MoS2 can be optically excited with the pulses from a femtosecond laser. These phonon modes can be optically dressed due to near-field interaction in the hybrid Ag-MoS2 system under an optical excitation resonant to localized plasmon modes. The coherent dynamics of the carriers in MoS2 were manipulated by the generation of dressed phonons. The driving field creates a coherence between the ground levels in the presence of optical near-field. A strong coupling between the exciton and plasmon modes forming a plexciton band is observed at room temperature within the coherence lifetime of the system. A significant enhancement of photoluminescent (PL) emission from MoS2 monolayer occurs due to carrier density modulation in the presence near-field interactions.
The absorption and emission properties of MoS2 are influenced due to the interactions with the semiconducting substrate. The coupling of carriers in MoS2 with the interfacial phonons, and the charge and energy transfer across the interface in 2D MoS2-GaN (0001) significantly change the UF absorption properties and the relaxation of carriers from the excitonic absorption states. An increased light absorption and enhanced PL emission from the single atomic layer of MoS2 was observed. The phonon-assisted processes can activate the dipole forbidden transitions and hence can explain the interaction of incident light in single atomic layer of MoS2. The MoS2-GaN heterostructure provides a platform to exploit strong coupling between the free carriers or excitons, plasmons and phonons. The gold (Au) NPs have a plasmon energy resonant to MoS2 and hence results in the strong exciton-plasmon coupling due to near-field interaction. In the meantime, the localized plasmon energy of platinum (Pt) NPs is selected to be in resonance to GaN bandedge emission and resonant to C excitonic state in MoS2. The localized plasmons in Pt can actively interact with carriers in MoS2 near Γ-point. The non-equilibrium absorption characteristics of MoS2 nanosheets on GaN hybridized with Au and Pt NPs are influenced due to activation of the defect levels of GaN induced due to interband optical excitation.
| Identifer | oai:union.ndltd.org:unt.edu/info:ark/67531/metadc1609107 |
| Date | 12 1900 |
| Creators | Poudel, Yuba R |
| Contributors | Neogi, Arup, Krokhin, Arkadii, Lin, Yuankun, Choi, Wonbong, D'Souza, Francis |
| Publisher | University of North Texas |
| Source Sets | University of North Texas |
| Language | English |
| Detected Language | English |
| Type | Thesis or Dissertation |
| Format | xii, 124 pages, Text |
| Rights | Use restricted to UNT Community, Poudel, Yuba R, Copyright, Copyright is held by the author, unless otherwise noted. All rights Reserved. |
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