Transient analysis in Al-doped barium strontium titanate thin films grown by pulsed laser deposition

Abstract

Thin films of (Ba_0.5Sr_0.5)TiO₃ (BST) with different concentrations of Al doping were grown using a pulsed laser deposition technique. dc leakage properties were studied as a function of Al doping level and compared to that of undoped BST films. With an initial Al doping level of 0.1 at.% which substitutes Ti in the lattice site, the films showed a decrease in the leakage current, however, for 1 at.% Al doping level the leakage current was found to be relatively higher. Current time measurements at elevated temperatures on 1 at.% Al doped BST films revealed space-charge transient type characteristics. A complete analysis of the transient characteristics was carried out to identify the charge transport process through variation of applied electric field and ambient temperature. The result revealed a very low mobility process comparable to ionic motion, and was found responsible for the observed feature. Calculation from ionic diffusivity and charge transport revealed a conduction process associated with an activation energy of around 1 eV. The low mobility charge carriers were identified as oxygen vacancies in motion under the application of electric field. Thus a comprehensive understanding of the charge transport process in highly acceptor doped BST was developed and it was conclusive that the excess of oxygen vacancies created by intentional Al doping give rise to space-charge transient type characteristics.