Engineering topological superlattices and their epitaxial integration in selectively grown hybrid nanostructures via MBE

The realization of advanced spintronics applications including the topological quantum computation, spin manipulation for data storage, dissipation less ballistic transport for ultra-fast quantum devices and topological switching for low energy memory applications etc. became more feasible with the experimental discovery of 3D topological insulators (TIs). The incorporation of exotic spin-momentum locked Dirac surface states (of 3D TIs) into these futuristic complex quantum devices requires not only the growth of high crystal quality epilayers but also the fabrication of pristine nanostructures, topological band engineering, ultra-smooth and defect-free surfaces, and atomically transparent epitaxial interfaces. This work deals with a systematic study of epitaxial growth of convention 3D TIs via molecular beam epitaxy(MBE) and atomic-scale structural characterization via scanning transmission electron microscope (STEM)to explore the above mentioned requirements. At first, the relation between the growth parameters and the defect density in the Van-der-Waals (VdW) based layered structures is investigated. The optimum growth parameters are extracted and the defect-free epilayers are prepared. Later, the technique of selective area epitaxy (SAE) is explored to develop a platform to achieve a scalable nano-architecture. Utilizing CMOS compatible fabrication technology, Si (111) substrates with crystalline and amorphous combinational surfaces are prepared. The precisely controlled growth parameters facilitated the realization of selectively grown topological structure. Based on statistical analysis, a generalized growth model is established that provided control over structural defects through the effective growth rate at the nanoscale and assisted in achieving high quality nanostructures. Based on conventional 3D TIs, the capabilities of VdW epitaxy are exploited further with the growth of topological-trivial hetero structures. The stoichiometric adjustment in these hetero structures is utilized as a tool to control ...