Thickness dependent charge transport in ferroelectric BaTiO₃ heterojunctions

We have investigated the effect of ferroelectric barium titanate (BaTiO₃) film thickness on the charge transport mechanism in pulsed laser deposited epitaxial metal-ferroelectric semiconductor junctions. The current (I)-voltage (V) measurements across the junctions comprising of 20-500nm thick BaTiO₃ and conducting bottom electrode (Nb: SrTiO₃ substrate or La_2/3Ca_1/3MnO₃ buffer layer) demonstrate the space charge limited conduction. Further analysis indicates a reduction in the ratio of free to trapped carriers with increasing thickness in spite of decreasing trap density. Such behaviour arises the deepening of the shallow trap levels (<0.65eV) below conduction band with increasing thickness. Moreover, the observed hysteresis in I-V curves implies a bipolar resistive switching behaviour, which can be explained in terms of charge trapping and de-trapping process.