Towards Scalable Electronics: Synthetic 2D Materials for Large-Area 2D Circuit Integration

In the past decades, a significant increase of the transistor density on a chip has led to exponential growth in computational power driven by Moore's law. To overcome the bottleneck of traditional von-Neumann architecture in computational efficiency, efforts are being dedicated to the development of alternative architectures that can seamlessly integrate computation and memory, such as in-memory computing. However, it still remains challenging in a suitable material system to fully harness the potential of this architecture. A noteworthy direction in this pursuit is the exploration of large-area 2D circuits based on two-dimensional (2D) materials and their heterostructures, leveraging their extraordinary properties such as the nano-scale thickness, outstanding electrical properties, and mechanical robustness. This motivates this thesis work to develop a scalable method of 2D material synthesis and exploit them as a promising platform for next-generation electronic devices.To this end, the first part of this thesis work explores the chemical vapor deposition (CVD) growth and electrical properties of individual TMDC materials. First, 2-inch wafer-scale monolayer MoS2 film is synthesized on a sapphire substrate. Several growth parameters, like the usage of NaCl and the etching-gas (O2 and H2), are studied to achieve a continuous and uniform film with a high crystalline quality. The 2-inch MoS2 film is then used as active channel material in in-memory computing devices and proved its potential to extend Moore's law. Second, large-area NbS2 single crystals are synthesized by CVD method. The growth morphologies are studied by changing the amount of Nb precursor, growth temperature and H2S:Ar ratio. A transition from a metallic 3R-polytype to a superconducting 2H-polytype is observed depending on the thickness of NbS2. A Berezinskii-Kosterlitz-Thouless (BKT) superconducting transition occurs in the CVD-grown 2H-phase NbS2 below the transition temperature of 3 K, opening up new possibilities for scalable and practical applications of superconductors in electronic and quantum devices.The second part of this thesis work focuses on developing synthesis method and studying the electrical properties of MoS2-NbS2 heterostructures. First, MoS2-NbS2 lateral heterostructures is grown by "one-step" MOCVD route with the monolayer MoS2 substitutionally doped with Nb atoms, resulting in a p-type transport behavior. The heterojunction shows a p-type transfer characteristic with a high on/off current ratio of around 10E4. The band structure through the MoS2-NbS2 heterojunction is investigated by temperature-dependent electrical measurements, DFT and quantum transport simulations. Second, NbS2-MoS2 patterned heterostructures is produced by a "two-step" route, combining MOCVD and sulfurization. The heterojunction is used as an active channel material with novel 2D contacts to develop field-effect transistors, in-memory devices and wafer-scale 2D circuits. Compared to pristine MoS2, the heterostructure performs a lower contact resistance and Schottky barrier height, resulting in a significant enhancement of the memory window and on/off current. The synthesis of MoS2-NbS2 heterostructures enables the creation of tailored 2D materials with enhanced electrical properties, showcasing their potential to revolutionize electronic and quantum device technologies.