Controlling Transport Properties of 2D Electron System Hosted by SrTiO3‐Based Bilayers

Abstract

Compared with the conventional 2D electron system (2DES) located between the LaAlO3 layer and SrTiO3 substrate, the LaAlO3/SrTiO3 bilayers are also capable of hosting 2DES with additional functional tunabilities. Herein, the LaAlO3 and SrTiO3 layers are epitaxially grown on the (La,Sr)(Al,Ta)O3 substrate to build a bilayer 2DES. The transport properties can be subtly tuned by the SrTiO3 layer thickness (tSTO), growth temperature (TG), and oxygen pressure (PO2), leading to various controllable electronic states. For the metallic bilayer 2DES, the low‐temperature carrier density (≈1014 cm−2) is one‐order‐of‐magnitude higher than that of the conventional 2DES (1012–1013 cm−2). Meanwhile, the bilayer 2DES exhibits the enhanced carrier mobility on increasing the carrier density, which contradicts the experimental results obtained from the conventional 2DES and suggests an important role of charge screening in the high‐carrier‐density bilayer 2DES. Moreover, the semiconducting bilayer 2DES, featured by the lower carrier density and thus less charge screening, shows the low‐field negative minimum and enhanced fourfold anisotropy in magnetoresistances. Those results infer that the majority of scattering centers shall be interfacial localized Ti3+ ions, which are screened by the high carrier density in the metallic bilayer 2DES.