Strain-driven sign interchange of surface two-dimensional electron and hole gases in KTaO3 thin film

TL;DR

This study demonstrates that applying biaxial stress to KTaO3 thin films can reversibly switch the surface 2D electron and hole gases, enabling strain-controlled manipulation of carrier types for potential device applications.

Contribution

It reveals a strain-driven sign interchange of surface 2D electron and hole gases in KTaO3, a phenomenon not previously reported, with detailed analysis of the underlying electrostatic potential reversal.

Findings

Carrier sign interchange occurs at a critical compressive strain.

Surface 2D carrier gases persist with overlayers and substrates.

Strain affects carrier concentration and effective mass.

Abstract

Since the discovery of two-dimensional (2D) electron gas in LaAlO3/SrTiO3 interface, 2D carrier gases in perovskite oxides have attracted great attention because they can host many important phenomena and may produce novel functional devices. Here, we show that there is one pair of surface 2D electron and hole gases in KTaO3 thin film and they can be tuned by applying biaxial stress. For increasing compressive in-plane strain, the 2D carrier concentrations decrease down to zero, and then a new pair of surface 2D electron and hole gases are formed and the carrier signs are interchanged. Our analysis indicates that this carrier sign interchange happens because the increasing compressive strain reverses the slope of monolayer-resolved electrostatic potential along the [001] direction. Furthermore, we also present strain-dependent carrier concentrations and effective masses and their thickness dependence, and show that the surface 2D carrier gases and their strain-driven sign interchange can persist even in the presence of overlayers and epitaxial substrates. These phenomena should be useful to design novel functional devices.