Study of the electrical properties of pulsed laser ablated (Ba_0.5Sr_0.5)TiO₃ thin films

Abstract

The laser ablated barium strontium titanate (BST) thin films were characterized in terms of composition, structure, microstructure and electrical properties. Films deposited at 300° C under 50 mTorr oxygen pressure and 3 J cm^-2 laser fluence and further annealed at 600° C in flowing oxygen showed a dielectric constant of 467 and a dissipation factor of 0.02. The room-temperature current-voltage characteristics revealed a space charge limited conduction (SCLC) mechanism, though at low fields the effect of the electrodes was predominant. The conduction mechanism was thoroughly-investigated in terms of Schottky emission at low fields, and bulk-limited SCLC at high fields. The change over to the bulk-limited conduction process from the electrode-limited Schottky emission was, attributed to the process of tunneling through the electrode interface at high fields resulting into the lowering of the electrode contact resistance and consequently giving rise to a bulk limited conduction process. The predominance of SCLC mechanism in the films suggests that the bulk properties are only revealed if the depletion width at the electrode interface is thin enough to allow the tunneling process to take place. This condition is only favorable if the film thickness is high or if the doping concentration is high enough. In the present case the film thickness ranged from 0.3 to 0.7 µ m which was suitable to show the transition mentioned above.