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.

Capping-layer-mediated lattice mismatch and redox reaction in SrTiO3-based bilayers

“…In this paper, different SrTiO 3 bilayers, consisting of various capping layers and the epitaxial SrTiO 3 layer, were grown on the (001)-oriented (La 0.7 Sr 0.3 )(Al 0.65 Ta 0.35 )O 3 (LSAT) substrates using pulsed laser deposition with reflection highenergy electron diffraction. Here, the TiO 2 -terminated surface can be inferred in our epitaxial SrTiO 3 layer grown on the LSAT [41] and SrTiO 3 substrates. For SrTiO 3 bilayers with various crystalline capping layers, the growth parameters for both SrTiO 3 and capping layers are as follows: 2 J cm −2 for the laser energy, 770 • C for the temperature and 10 −6 mbar for the oxygen pressure.…”