Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO3 interface: Control of oxygen vacancies

In this paper, we report on the highly conductive layer formed at the crystalline gamma-alumina/SrTiO3 interface, which is attributed to oxygen vacancies. We describe the structure of thin gamma-alumina layers deposited by molecular beam epitaxy on SrTiO3 (001) at growth temperatures in the range of 400-800 degrees C, as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. In situ x-ray photoelectron spectroscopy was used to confirm the presence of the oxygen-deficient layer. Electrical characterization indicates sheet carrier densities of similar to 10(13) cm(-2) at room temperature for the sample deposited at 700 degrees C, with a maximum electron Hall mobility of 3100 cm(2)V(-1) s(-1) at 3.2 K and room temperature mobility of 22 cm(2)V(-1)s(-1). Annealing in oxygen is found to reduce the carrier density and turn a conductive sample into an insulator. (C) 2015 AIP Publishing LLC.