Coexisting two-dimensional electron and hole gases highly confined at the interfaces of undoped KTaO3-sandwiching heterostructures

TL;DR

This study predicts highly confined coexisting two-dimensional electron and hole gases at interfaces in undoped KTaO3-based heterostructures, revealing potential for novel oxide electronic devices through first-principles analysis.

Contribution

It introduces the existence of coexisting 2DEG and 2DHG at KTaO3 interfaces, driven by polar discontinuity and stress-induced polarization, a novel finding in oxide heterostructures.

Findings

Coexisting 2DEG and 2DHG are highly confined at KTaO3 heterostructure interfaces.

Electron and hole carriers originate from specific atomic orbitals at the interfaces.

Carrier concentrations are on the order of 10^13 cm^-2.

Abstract

Two-dimensional electron gas (2DEG) in interfaces and surfaces based on perovskite SrTiO$_3$ (STO) has exhibited various interesting phenomena and is used to develop oxide electronics. Recently, KTaO$_3$ (KTO) shows great potential and is believed to host more exciting effects and phenomena toward novel devices. Here, through first-principles investigation and analysis, we find two types of coexisting 2DEG and 2D hole gas (2DHG) highly confined at the interfaces in undoped STO/KTO/BaTiO$_3$ heterostructures, when the KTO thickness $m$ reaches a crititcal value. The two interfaces are made by (SrO)$^0$/(TaO$_2$)$^+$ and (KO)$^-$/(TiO$_2$)$^0$ for the A-type, and by (TiO$_2$)$^0$/(KO)$^-$ and (TaO$_2$)$^+$/(BO)$^0$ for the B-type. The 2D electron carriers originate from Ta-$5 d_{xy}$ states at the interface including TaO$_2$ atomic layer, and the hole carriers from O-$2 p_x/p_y$ orbitals at the other interface. The electron and hole effective masses are 0.3$m_0$ and $1.06\sim 1.12 m_0$, respectively, where $m_0$ is mass of free electron, and the 2D carrier concentrations are in the order of $10 ^{13}$ cm$^{-2}$. Our analysis indicates that the interfacial 2DEG and 2DHG are simultaneously formed because of the band bending due to the polar discontinuity at the interfaces and the stress-induced polarization within the KTO layer. These could stimulate more exploration for new phenomena and novel devices.