We report strong localization of two-dimensional electron gas in LaAlO${}_3$/SrTiO${}_3$ epitaxial thin-film heterostructures grown on (LaAlO${}_3$)${}_{0.3}$-(Sr${}_2$AlTaO${}_3$)${}_{0.7}$ substrates by using pulsed laser deposition with in situ reflection high-energy electron diffraction. Using longitudinal and transverse magnetotransport measurements, we have determined that disorder at the interface influences the conduction behavior, and that increasing the carrier concentration by growing at lower oxygen partial pressure changes the conduction from strongly localized at low carrier concentration to metallic at higher carrier concentration, with indications of weak localization. We interpret this behavior in terms of a changing occupation of Ti 3$d$ bands near the interface, each with a different spatial extent and susceptibility to localization by disorder, and differences in carrier confinement due to misfit strain and point defects.

• Received 17 October 2011

DOI:https://doi.org/10.1103/PhysRevB.85.161407