Influence of the vicinal substrate miscut on the anisotropic two-dimensional electronic transport in Al2O3–SrTiO3 heterostructures

Abstract

The electrical resistance of the two-dimensional electron system (2DES) which forms at the interface of SrTiO3 (STO)-based heterostructures displays anisotropic transport with respect to the direction of current flow at low temperature. We have investigated the influence of terraces at the surface of STO substrates from which the 2DES is prepared. Such terraces are always present in commercially available STO substrates due to the tolerance of surface preparation, which result in small miscut angles of the order of γ ≈ 0.1° with respect to the surface normal. By a controlled increase of the substrate miscut, we could systematically reduce the width of the terraces and thereby increase the density of substrate surface steps. The in-plane anisotropy of the electrical resistance was studied as a function of the miscut angle γ and found to be mainly related to interfacial scattering arising from the substrate surface steps. However, the influence of γ was notably reduced by the occurrence of step-bunching and lattice-dislocations in the STO substrate material. Magnetoresistance (MR) depends on the current orientation as well, reflecting the anisotropy of carrier mobility. For γ ≥ 2°, MR is substantially enhanced and shows the trend toward a linear field dependence, which is typical for inhomogeneous conductors. From weak-antilocalization observed at the small magnetic field, we deduce information on inelastic scattering and spin–orbit coupling. While the field scale associated with a Rashba-type spin–orbit coupling in 2D weak-localization does not show a pronounced correlation with γ, distinct changes of the scale are associated with inelastic scattering.