Growth, Optoelectronic Properties, and Defect Engineering of CVD 2D-TMD-based Heterostructures

Abstract

This thesis presents a comprehensive exploration of the growth, optoelectronic properties, and defect engineering of CVD 2D-TMD-based heterostructure. In the first phase, the thesis focuses on improving implied open-circuit voltage (iVoc) of MoS2 materials through passivation techniques grown by using traditional CVD method. By reducing recombination losses and enhancing material stability, these passivation methods further optimize the performance MoS2 monolayer. Then, the optimalization study begins with the growth of high-luminescence monolayer MoS2 using a single-salt catalyst system via chemical vapor deposition (CVD). By utilizing sodium nitrate (NaNO3), the crystal quality and luminescence of the monolayers are significantly enhanced, providing a solid foundation for further material development. Building on this, the research progresses to more complex catalyst systems, where hybrid alkali salt catalysts (NaCl, NaNO3, PTAS) are employed to grow MoSe2-WSe2 lateral heterostructures. These multi-salt catalysts allow for precise control over heterostructure formation, resulting in tunable optoelectronic properties that surpass those of simple monolayers. The final phase of the thesis explores the synthesis of ordered-disordered alloys, specifically Mo(1-x)WxSe2, where nanoscale domains of MoSe2 and WSe2 coexist within a single material. This novel structure leads to unique light-matter interactions, such as interfacial excitons and enhanced valley polarization up to 50%, which are not observed in purely ordered systems. These alloys also demonstrate improved optoelectronic performance, particularly in terms of implied open circuit voltage, indicating their strong potential for use in high-efficiency photovoltaic devices. Overall, this work illustrates a coherent progression from fundamental material synthesis to advanced heterostructure development and optimization, culminating in the demonstration of high-performance optoelectronic and photovoltaic devices based on 2D TMDs.