Abstract
The single-crystal SrTiO3 (001) has two different surface terminations, TiO2 and SrO. One most remarkable observation in previous studies is that only the heterointerfaces with TiO2-terminated SrTiO3, which usually combines with polar oxides such as LaAlO3, host an electron gas. Here we show that a robust electron gas can be generated between a non-polar oxide, CaHfO3, and SrTiO3 (001) with either termination. Unlike the well-known electron gas of LaAlO3/SrTiO3, the present one of CaHfO3/SrTiO3 essentially has no critical thickness of CaHfO3, can survive a long-time oxygen annealing at high temperature, and its transport properties are stable under exposure to water and other polar solvents. By electrostatic gating through CaHfO3, field-effect devices are demonstrated using CaHfO3/SrTiO3 heterointerfaces with both terminations. These results show that the electron gas reported in the present study is unique and promising for applications in oxide electronics.
Highlights
The single-crystal SrTiO3 (001) has two different surface terminations, TiO2 and SrO
One most remarkable result in previous studies is that the electron gas (EG) can only be formed on TiO2-terminated STO (T-STO), and the heterointerface with SrO-terminated STO (S-STO) is highly insulating[1,13]
As far as robustness is concerned, it is rare that these heterointerfaces, no matter formed with polar, non-polar, or amorphous oxides, can be comparable with LaAlO3/STO because their EGs quickly vanish after annealing in oxygen at moderate temperatures, i.e. 300 °C or lower[19]
Summary
The single-crystal SrTiO3 (001) has two different surface terminations, TiO2 and SrO. By electrostatic gating through CaHfO3, field-effect devices are demonstrated using CaHfO3/SrTiO3 heterointerfaces with both terminations These results show that the electron gas reported in the present study is unique and promising for applications in oxide electronics. One most remarkable result in previous studies is that the EG can only be formed on TiO2-terminated STO (T-STO), and the heterointerface with SrO-terminated STO (S-STO) is highly insulating[1,13] This extreme asymmetry originates from the polar arrangement of atomic layers in LaAlO3, and can be understood in an elegant polar discontinuity and electronic reconstruction picture[13]. As far as robustness is concerned, it is rare that these heterointerfaces, no matter formed with polar, non-polar, or amorphous oxides, can be comparable with LaAlO3/STO because their EGs quickly vanish after annealing in oxygen at moderate temperatures, i.e. 300 °C or lower[19]. We show that the interface between epitaxial CHO and STO can be metallic as well
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