Improving Transport in Complex Oxide Heterostructures: High Density 2DELs and High Mobility Stannates

Perovskite oxides present a wide range of electronic and magnetic properties that set them apart from traditional semiconductors like Si or III--V compounds. However, such properties are yet to be fully harvested in developing new electronic devices with advanced functionalities. The discovery of high density, two-dimensional electron liquids (2DELs) in oxide thin films has shown promise for the advancement of oxide electronics. Yet, many fundamental properties of these electron liquids remain unclear. Another major impediment in developing functional oxide devices is poor electrical conductivities in most perovskite oxide semiconductors. To that end, this work utilizes oxide molecular beam epitaxy (MBE) to develop new geometries in titanate heterostructures that improve our fundamental understanding of electrical transport in high density oxide 2DELs. This work also pursues growth of a new class of perovskite thin films, alkali-earth stannates, for increased room temperature electrical conductivities in complex oxides.In this thesis, I discuss the origin and underlying transport mechanisms in 2DELs at (001) and (111) SrTiO3/RTiO3 (R: rare earth atom) interfaces. By utilizing new titanate devices, we study the sub-band characteristics of 2DELs in SrTiO3. The high density 2DELs are also utilized to answer long-standing fundamental questions about ferroelectricity and its coexistence with metallicity in BaTiO3. Finally, we present approaches in oxide MBE used to develop high quality films of BaSnO3 with improved electrical transport characteristics, featuring room temperature mobilities exceeding 170 cm2/Vs at carrier densities > 5E19 cm3. Growth of high quality SrSnO3 and BaxSr1-xSnO3 films and their structural and optical properties will also be discussed. It will be shown that a combination of the different techniques developed in this thesis has lead to new avenues of research in advancing the goal of functional oxide electronics