Localized electronic states induced by defects and possible origin of ferroelectricity in strontium titanate thin films

TL;DR

This study investigates how defects, especially oxygen vacancies, induce localized electronic states in strontium titanate thin films, potentially explaining their ferroelectric behavior at room temperature.

Contribution

First-principles calculations show oxygen vacancy complexes create localized states, suggesting defect engineering as a route to ferroelectricity in STO thin films.

Findings

Oxygen vacancies create deep localized states in STO.

Electronic structural changes align with optical and X-ray data.

Defects may be exploited to induce ferroelectricity.

Abstract

Several defect configurations including oxygen vacancies have been investigated as possible origins of the reported room-temperature ferroelectricity of strontium titanate (STO) thin films [Appl. Phys. Letts. 91, 042908 (2007)]. First-principles calculations revealed that the Sr-O-O vacancy complexes create deep localized states in the band gap of SrTiO3 without affecting its insulating property. These results are in agreement with electronic structural changes determined from optical transmission and X-ray absorption measurements. This work opens the way to exploiting oxygen vacancies and their complexes as a source of ferroelectricity in perovskite oxide thin films, including STO.