Improved cationic stoichiometry and insulating behavior at the interface of LaAlO₃/SrTiO₃ formed at high oxygen pressure during pulsed-laser deposition

¹ Department of Microtechnology and Nanoscience - MC2, Chalmers University of Technology Göteborg, Sweden, EU
² Ioffe Physico-Technical Institute RAS - St. Petersburg, Russia
³ Department of Applied Physics, Chalmers University of Technology - Göteborg, Sweden, EU
⁴ Skobeltsyn Institute of Nuclear Physics, Moscow State University - Moscow, Russia

^a alexei.kalaboukhov@chalmers.se

Received: 12 October 2010
Accepted: 17 January 2011

Abstract

Medium-energy ion spectroscopy, MEIS, and scanning transmission electron microscopy, STEM, were used to correlate the atomic structure of LaAlO₃/SrTiO₃ interfaces with their electrical properties. Interfaces were prepared at high (5×10⁻² mbar) and low (10⁻⁴ mbar) oxygen pressure by pulsed-laser deposition. The high-oxygen-pressure heterostructures were insulating for all thicknesses while the low-oxygen-pressure ones became metallic for thicknesses above 4 unit cells. MEIS data show enhancement of the Sr surface peak and suppression of the La one in interfaces prepared at low oxygen pressure, which is interpreted as a La-Sr intermixing. The effect was considerably smaller in high-oxygen-pressure samples. Analysis of high-angle annular-dark-field STEM images of the LAO films also indicates intermixing between La and Sr in low-oxygen-pressure samples, supporting MEIS data. Our results reveal the important role of oxygen pressure on the formation of the interface electron gas.