Chemical Vapor Deposition of Molybdenum Disulfide for Optoelectronic Device Applications

Abstract

The growth of two-dimensional (2D) transition metal dichalcogenides, especially molybdenum disulfide (MoS2), has become a focus of research owing to their potential in next-generation electronic and optoelectronic applications. Although numerous studies have demonstrated the excellent electronic and optoelectronic properties of mechanically exfoliated MoS2, the reliance on exfoliation and transfer processes severely limits scalability and practical device integration. These limitations show the need for scalable and epitaxial growth techniques to enable broader technological applications. In this thesis, we focus on chemical vapor deposition (CVD) as a scalable synthesis method for MoS2 and explore its application in optoelectronic devices. In Chapter 1, we detail the fundamental properties of MoS2 and discuss its potential in electronic and optoelectronic applications. We show the limitations of commonly used mechanical exfoliation and transfer-based approaches and emphasize the necessity of epitaxial growth methods. Based on these limitations, we define the objectives of this thesis to investigate CVD growth parameters for MoS2 and to demonstrate MoS2 LEDs. The motivation for studying CVD-grown MoS2 and its application in light-emitting devices is also presented. In Chapter 2, a detailed literature review is provided. The electronic and optical characteristics of MoS2, including bandgap and spin-orbit coupling, are discussed, followed by a review of MoS2 synthesis techniques from mechanical exfoliation to CVD. The status and challenges of scalable and epitaxial MoS2 growth systems are also addressed. In Chapter 3, we describe the experimental methods employed in this study. We first introduce our CVD growth system and the experimental growth profiles used to synthesize MoS2. We then explain the characterization techniques used to evaluate the grown MoS2, including scanning electron microscopy, Raman spectroscopy, photoluminescence spectroscopy, and X-ray diffraction. Device fabrication and characterization methods are also described. In Chapter 4, we focus on the optimization of CVD growth conditions for MoS2, which represents the main experimental contribution of this research. We investigated the growth of MoS2 on different substrates and studied the effects of growth temperature. Subsequently, we examined the influence of growth time on MoS2 layers. Through these studies, we identified optimized growth conditions that enabled the formation of continuous and uniform MoS2 layers. In Chapter 5, we present our research on an epitaxial MoS2 LED. We fabricated a ZnO/MoS2/GaN heterostructure and investigated its electrical and optical properties. The electrical and optical performance of the fabricated LED was analyzed, demonstrating the feasibility of CVD-grown MoS2 for light-emitting applications. Chapter 6 summarizes the overall conclusions of this thesis and discusses future research directions.