Highly conductive two-dimensional electron gas at the interface of Al 2 O 3 /SrTiO 3

We create a two-dimensional electron gas at the Al2O3/SrTiO3/LaAlO3 heterostructures using pulsed laser deposition, which exhibits a decreasing sheet resistance with increasing growth temperatures of Al2O3 films. Structural characterizations of films are confirmed by cross-sectional transmission electron microscopy. Compared with these heterostructures with Al2O3 films deposited on pristine SrTiO3 and TiO2-terminated SrTiO3 substrates, the Al2O3/SrTiO3/LaAlO3 heterostructures are more conductive. X-ray photoelectron spectroscopy indicates the formation of oxygen vacancies at the SrTiO3 side of the interface, which results from the redox reactions by reducing SrTiO3 films. Furthermore, the existence of oxygen vacancies on the SrTiO3 side is verified by a blue-light emission.