Two-dimensional electron gas at the epitaxial alumina/SrTiO$_{3}$ interface: control of oxygen vacancies

A highly interesting application for SrTiO$_{3}$ involves the formation of a high mobility two-dimensional electron gas (2DEG) at the oxide/oxide interface. We report on the conducting layer formed at the crystalline $\gamma $-alumina/SrTiO$_{3}$ (STO) interface which is attributed to oxygen vacancies. We describe the structure of thin $\gamma $-alumina layers deposited by molecular beam epitaxy on STO (001), as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. \textit{In-situ} x-ray photoelectron spectroscopy was used to confirm the presence of oxygen vacancies at the interface. Electrical characterization indicates a higher sheet resistance for lower deposition temperature. A maximum electron Hall mobility of 3100 cm$^{2}$V$^{-1}$s$^{-1}$ at 3.2 K and room temperature mobility of 22 cm$^{2}$V$^{-1}$s$^{-1}$ are measured.