Thesis
Study of substrate-induced effect on CVD-grown MoS₂ thin films
Master of Science (M.S.), Drexel University
Jun 2018
DOI:
https://doi.org/10.17918/4pqe-0r83
Abstract
Two-dimensional (2D) materials have become a hot topic in materials research since the successful isolation of stable graphene through mechanical exfoliation. Graphene has many attractive properties however it has zero bandgap, which limits its application as a transistor material in logical circuits. The transition metal dichalcogenides (TMDCs) family has emerged as a promising alternative due to their excellent semiconductor properties. Among various TMDC materials, MoS₂ has received the most intensive research due to an indirect bandgap to direct bandgap transition when its thickness is reduced from bulk to a monolayer. Chemical vapor deposition (CVD) has become a popular technique to synthesize TMDC and MoS₂ atomically thin films in large-scale, excellent quality and low cost. However, little work has been done to study the properties of CVD-grown MoS₂ on functional perovskite substrates such as SrTiO₃ (STO) and (LaAlO₃)_[0.3](Sr₂TaAlO₆)_[0.7] (LSAT). In this work, MoS₂ atomically thin films were synthesized via CVD on various substrates including SiO₂, Al₂O₃ (0001), STO (001) and LSAT (001). The obtained MoS₂ islands were characterized by optical microscopy and atomic force microscopy (AFM) to show their morphology and confirm their thickness. Subsequently, Raman and photoluminescence (PL) spectroscopy were employed to characterize the substrate-induced effect on as-grown MoS₂ thin films. From Raman spectroscopy, it was confirmed that the synthesized MoS₂ crystals were 1-4 atomic layers and no prominent substrate-induced strain was found, which may be due to the weak van der Waals interaction between substrate and MoS₂. PL spectra revealed significant substrate-induced charge doping effect on MoS₂ which changes the relative population of trions and neutral excitons and as a result modifies the PL spectra. The charge doping was quantified by estimating the electron density in MoS₂ on different substrates based on a three-level model and mass-action model between trions, neutral excitons and free electrons. It is anticipated that this thesis study can help to provide a feasible route to tailor the electronic properties of TMDC-based heterostructures as needed to enable novel device design in the future via substrate engineering.
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Details
- Title
- Study of substrate-induced effect on CVD-grown MoS₂ thin films
- Creators
- Yuchen Hou - DU
- Contributors
- Steven J. May (Advisor) - Drexel University (1970-)
- Awarding Institution
- Drexel University
- Degree Awarded
- Master of Science (M.S.)
- Publisher
- Drexel University; Philadelphia, Pennsylvania
- Number of pages
- 108 pages
- Resource Type
- Thesis
- Language
- English
- Academic Unit
- Materials (Science and) Engineering (Metallurgical Engineering) (1970-2026); College of Engineering (1970-2026); Drexel University
- Other Identifier
- 8241; 991014632318804721