Defect Engineering in Oxide Heterostructures by Enhanced Oxygen Surface Exchange

Abstract

The synthesis of materials with well-controlled composition and structure improves our understanding of their intrinsic electrical transport properties. Recent developments in atomically controlled growth have been shown to be crucial in enabling the study of new physical phenomena in epitaxial oxide heterostructures. Nevertheless, these phenomena can be infl uenced by the presence of defects that act as extrinsic sources of both doping and impurity scattering. Control over the nature and density of such defects is therefore necessary to fully understand the intrinsic materials properties and exploit them in future device technologies. Here, it is shown that incorporation of a strontium copper oxide nano-layer strongly reduces the impurity scattering at conducting interfaces in oxide LaAlO 3 -SrTiO 3 (001) heterostructures, opening the door to high carrier mobility materials. It is proposed that this remote cuprate layer facilitates enhanced suppression of oxygen defects by reducing the kinetic barrier for oxygen exchange in the hetero-interfacial fi lm system. This design concept of controlled defect engineering can be of signifi cant importance in applications in which enhanced oxygen surface exchange plays a crucial role.

Electronic Reconstruction at the Interface Between Band Insulating Oxides: The LaAlO3/SrTiO3 System

“…Moreover, the mobility of the q2DES in LAO/STO is strongly dependent on the deposition conditions and on the eventual presence of a capping layer. The record mobility values, up to 5x10 4 cm 2 V -1 s -1 demonstrated by the Twente group, were obtained on LAO/STO bilayers capped by an epitaxial cuprate SrCuO 2 film [7].…”

“…However, the discovery by Ohtomo and Hwang of a 2D-conductivity at the interface between two insulating oxides came as a surprise in view of the large band gaps of both LaAlO 3 (5.6 eV) and SrTiO 3 (3.2 eV). The LaAlO 3 /SrTiO 3 interface host a q2DES characterized by unique electronic properties, including respectable mobility exceeding 5x10 4 cm 2 V -1 s -1 (at 4.2 K) [7], low temperature superconductivity [8], and widely tuneable electric properties using electric field effect, which allows, for example, a control of metal to insulating transition [9][10] (even at room temperature) and a modulation of Rashba spin-orbit coupling over a large range [11].…”

Insulator-to-Metal Transition at Oxide Interfaces Induced by WO3 Overlayers

“…In order to promote high electron mobility, it is crucial to confine donor sites away from the conducting plane, without preventing the 2DES formation in the STO top layers. Previous attempts to control the defect concentration profile and thus enhance the mobility involved the use of crystalline insulating overlayers [14,15], adsorbates [16], amorphous materials [17] and even thin metallic layers [18,19]. A promising material to control defect formation is tungsten oxide WO 3 .…”

Tuning the conductivity threshold and carrier density of two-dimensional electron gas at oxide interfaces through interface engineering

“…1,6,19 Concurrently, a lot of efforts have been put in tailoring the electronic properties such as the density of 2DEG of the LAO/STO heterostructures, critical for utilizing the diverse functionality this 2DEG offers in nanoscale and multifunctional devices. 23 capping layer gave a lower carrier density than its original value, which might be explained due to defect engineering or the induced internal electric field in the LAO layer by the capping layer. In addition, the thickness threshold for producing conductivity can also be tuned by the introduction of the capping layer or by mixing a nonpolar with polar oxide in the overlayer.…”