The Two-dimensional Electron Gas at the Lanthanum Aluminate - Strontium Titanate Heterointerface

Since the discovery of the conducting two dimensional electron gas (2DEG) at the interface of insulating oxide materials LaAlO3 and SrTiO 3 in 2004, this system has shown a vast diversity of physical properties including superconductivity, ferromagnetism and field induced metal-insulator phase transitions. In this dissertation we discuss three advances by our collaboration that bolster applicability of this interfacial system. In an all thin-film LaAlO3/SrTiO3 system we identified two different conduction regimes, where the effect of oxygen partial pressure during growth directly affects the carrier density of the system. In the lower carrier density regime (∼ 1013 cm-2) we found a metallic to insulating temperature dependence and strong localization by disorder, whereas in the higher regime (> 1014 cm-2) we find metallic dependence with signs of weak localization. This is understood in the occupation of Ti 3d bands farther from the interface as carrier density is increased. Our work in the electronic properties of all-thin-film LaAlO 3/SrTiO3 pioneers the understanding and implementations of this 2DEG to harness the richness of this oxide interface and its integration to industry standard substrates. Furthermore, we showed the first conducting LaAlO3/SrTiO3 two-dimensional system grown by the physical vapor deposition technique: 90° off-axis sputtering. Films grown with this scalable technique have excellent crystalline quality and transport characteristics similar to those grown by (mostly research employed) pulsed laser deposition. Writing of circuits on the nanoscale using conducting-tip atomic force microscopy is demonstrated in sputtered LaAlO3 on SrTiO3, opening the doors to nanoelectronic application of this novel interfacial system. Moreover, we are among the first groups in the world to demonstrate conducting [111]-oriented LaAlO3/SrTiO3 heterostructures, a crystallographic orientation that proves to be challenging due to the large polar nature of perovskite oxides in this stacking direction. An interplay between structural and electronic reconstructions is at work to resolve the polarization divergence. This drives the LaAlO3/SrTiO 3 (111) system from insulating to conducting with increasing LaAlO 3 thickness, displaying a broader transition than the conventional (001) system and a similar n-type 2DEG.