Synthesis and characterization of two-dimensional transition metal dichalcogenides

Semiconducting transition metal dichalcogenides (TMDCs) have attracted intense research interest in recent years, due to their many unique electrical, optical, and mechanical properties and their potential for diverse applications. One of the key challenges in 2D TMDC electronics is to synthesize high-quality and large-scale monolayer TMDCs. In this thesis, I have systematically investigated the growth of MoS2 and WSe2 using chemical vapor deposition (CVD) and metal-organic chemical vapor deposition (MOCVD) methods. I studied the impact of the growth conditions, including temperature, pressure, gas flow rate, precursor type, precursor quantify, the position of the solid precursor, and seed layer dispersion, on the morphology of the MoS2 and WSe2 film. Optical imaging, Raman and photoluminescence (PL) spectroscopy, and atomic force microscopy (AFM) were used to measure the synthesized film. Electronic devices including transistors, Hall-bars and transmission line microstrips (TLMs) were fabricated. Current transport of these devices was measured at various temperatures. Based on the systematic investigation and process optimization, we were able to successfully grow monolayer WSe2 with grain size up to 30 micrometers. At room temperature, the carrier mobility reaches 7.5 cm2/V-s. In addition, we have successfully grown MoS2 using gas phase precursor H2S and molybdenum hexacarbonyl (MHC) for the first time. These gas phase precursors can potentially enable wafer scale growth of TMDCs. This study provides comprehensive information and in-depth understanding of the synthesis of WSe2 and MoS2 using CVD and MOCVD methods. The resulting monolayer WSe2 and MoS2 materials provide a solid material foundation for future study of the electronic and photonic devices based on these materials. These novel devices will have a broad range of applications in computing, communication, and biomedicine