Abstract
At present, the generation of heterostructures with two dimensional electron gas (2DEG) in amorphous LaAlO3 (a-LAO)/SrTiO3 (STO) has been achieved. Herein, we analysed thermal stability of 2DEG at a-LAO/STO interfaces in comparison with 2DEG at crystalline LaAlO3 (c-LAO)/STO interfaces. To create 2DEG at LAO/STO interface, regardless of growing temperature from 25 to 700 °C, we found that environment with oxygen deficient during the deposition of LAO overlayer is essentially required. That indicates that the oxygen-poor condition in the system is more essential than the crystalline nature of LAO layer. 2DEG at a-LAO/STO interface is depleted upon ex situ annealing at 300 °C under 300 Torr of oxygen pressure, while that in c-LAO/STO interface is still maintained. Our result suggests that the LAO overlayer crystallinity critically affects the thermal-annealing-induced depletion of 2DEG at a-LAO/STO interface rather than the generation of 2DEG. We clearly provide that amorphous TiOx can efficiently prevent the thermal degradation of 2DEG at the a-LAO/STO interface, which gives a cornerstone for achieving thermal-stable 2DEG at a-LAO/STO interface.
Highlights
Oxide-based complex materials having strongly correlated electrons play a crucial role in a wide variety of physical phenomena and have potential for applications in exotic fields such as charge-ordered insulators, high temperature superconductivity, unconventional ferroelectricity and double exchange ferromagnets [1,2,3]
The amorphous LaAlO3 (a-LAO)/STO (Fig. 1a) and crystalline LaAlO3 (c-LAO)/STO (Fig. 1b) surfaces consist of regular steps and terraces structures that are inherent in the TiO2-terminated substrates
The height profiles of the a-LAO/STO and c-LAO/STO surfaces indicate that the step height is about 0.4 nm which corresponds to one unit-cell of LAO
Summary
Oxide-based complex materials having strongly correlated electrons play a crucial role in a wide variety of physical phenomena and have potential for applications in exotic fields such as charge-ordered insulators, high temperature superconductivity, unconventional ferroelectricity and double exchange ferromagnets [1,2,3]. Our electrical measurements reveal that the metallic conductivity at a-LAO/ STO heterointerfaces is obtained in oxygen-deficient growth conditions and that there is a critical thickness of the a-LAO overlayer for the 2DEG formation, which are very observed in c-LAO/STO heterointerfaces. A-LAO/STO shows much pronounced degradation in 2DEG conductivity compared with c-LAO/ STO with increasing ex situ annealing temperature, demonstrating that the crystallinity of the overlayer has little impact on the 2DEG formation but significantly affect the thermal stability of 2DEG in the STO-based heterointerfaces.
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