Tunability of conduction at the LaAlO_3/SrTiO_3 heterointerface: Thickness and compositional studies

摘要

The role of chemistry, film thickness, and oxygen pressure in influencing the electrical and thermal transport properties of LaAlO_3/SrTiO_3 heterointerfaces is explored. Unit-cell precise growth was accomplished for films between 3 and 160 unit cells thick using reflection high-energy electron diffraction-assisted pulsed-laser deposition. Subsequent temperature-dependent studies of electrical resistivity reveal three important observations: (1) by tuning the laser fluence, we can systematically tune the interfacial conductance in a step-wise manner in this system, (2) all films exhibit a critical thickness of 3-4 unit cells for the onset of conduction, and (3) the nature of the conductance is highly influenced by the stoichiometry of the LaAlO_3 film with La-deficient samples showing dramatic changes with thickness, while stoichiometric and La-excess films show little dependence. Time-domain thermoreflectance studies show a diminished interfacial thermal conductance for the La-deficient films when compared to La-excess and stoichiometric films, suggesting that the interfacial conductance is more influenced by extrinsic factors such as oxygen deficiency.