Quasi-two-dimensional electron gas at γ-Al₂O₃/SrTiO₃ heterointerfaces fabricated by spin coating method

Complex oxide heterointerfaces with the two-dimensional electron gas have drawn a lot of attention due to their emerging properties. However, most of them are prepared using the method with relatively high energy particles, which would inevitably lead to some defects. Here, a key challenge in the quasi-two-dimensional electron gas at spinel-type Al₂O₃/SrTiO₃ heterointerfaces using a spin coating method is addressed. The grown Al₂O₃ films have the atomic-scale smooth surface and the thickness is about 70 nm. The γ-Al₂O₃ layer with a thickness of about 3 nm in proximity to SrTiO₃ and the amorphous Al₂O₃ layer on the top of γ-Al₂O₃ are observed for the heterointerface annealed at 800 °C. The heterointerfaces at annealed temperatures above 750 °C exhibit a metallic behavior, which is attributed to the dominant layer of γ-Al₂O₃. The sheet carrier density is about 3.1 × 10¹⁵ cm^-2 and the Hall mobility is 4924.4 cm² V^-1 s^-1 at 15 K at the heterointerface annealed at 800 °C. Our work provides a low-cost way for the large-scale and large-area production of two-dimensional electron gas at high-quality oxide interfaces.