Two-dimensional transition metal dichalcogenides (TMDs) are of great interest for the discovery of many novel physics owing to their extraordinary electrical, optical, mechanical properties as well as many promising applications including heterojunctions. To realize the overreaching goals of these materials, it is important to develop scalable growth techniques and investigate the role of different growth parameters on the resulting material properties. In this dissertation, I study, (i) controllable and reproducible growth of monolayer molybdenum disulfide (MoS2) via chemical vapor deposition (CVD), (ii) the role of growth temperature on the properties of large area MoS2 thin films grown via thermal vapor sulfurization route, and (iii) low temperature growth of palladium diselenide (PdSe2) thin films, their doping and integration into heterojunctions. In particular, for the growth of MoS2 monolayer crystals, I modified the CVD process by using molybdenum trioxide thin films as a precursor addressing the difficulty of controlling the local variations of the precursor concentrations in the conventional method resulting in highly reproducible MoS2 crystal growth. For large area MoS2 thin films, I show that the electrical properties of the samples change significantly with growth temperature and discuss the challenges in using Si/SiO2 substrates for the direct growth of these films, specially at high temperature. For PdSe2 thin films, I studied the changes in electrical, chemical, and crystalline quality of the PdSe2 films grown under low pressure CVD conditions below 400 C and showed its integration with molybdenum diselenide to fabricate a vertical heterojunction diode with a high rectification ratio. I have also investigated the surface charge transfer doping of PdSe2 devices and used it toward fabrication of lateral heterojunction diode by selective area doping. The TMD synthesis, doping, and heterojunction integrations shown in this study is a significant step forward for the scalable fabrication of photodetectors, sensors, logic circuits, and other high-performance electronic devices.
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Doctor of Philosophy (Ph.D.)
College of Sciences
Length of Campus-only Access
Doctoral Dissertation (Open Access)
Withanage, Sajeevi Sankalpani, "Chemical Vapor Deposition Growth of Transition Metal Dichalcogenides and Their Heterostructure Integration" (2021). Electronic Theses and Dissertations, 2020-. 587.