Impact of microstructure on electrical characteristics of laser ablation grown ZrTiO₄ on Si substrate

Abstract

Zirconium titanate thin films were deposited on a p-type Si substrate using the pulsed excimer laser ablation technique and the thin films were either highly oriented along (020) or were of a polycrystalline nature, depending upon the processing conditions. A detailed structural characterization using atomic force microscopy, scanning electron microscopy, x-ray photoelectron spectroscopy (XPS) and x-ray diffraction of the highly oriented and polycrystalline ZrTiO₄ thin films were carried out. The XPS of highly oriented ZrTiO₄ thin films deposited on Si substrates was characterized. The O 1s spectrum did not show any splitting, indicating there is no possibility of adsorbed oxygens, and the single peak in O 1s is attributed to the oxygen ions in the lattice. Capacitance-voltage (C-V), conductance-voltage (G-V) and dc leakage current studies were done on both types of thin film. Secondary ion mass spectrometer studies revealed a reasonably sharper interface existing at the thin film/substrate for the polycrystalline films, compared with the highly oriented thin films. A higher dielectric constant and higher leakage current were observed for the highly oriented ZrTiO₄ thin films compared with polycrystalline thin films. The C-V and G-V studies were carried in the frequency regime of 1-100 kHz on both types of film at higher temperatures (300-500 K) so as to make the minority carriers of the Si substrate respond to the applied ac modulating signal. The activation energies calculated from the Arrhenius plot from C-V and G-V measurements were nearly equal to half of the silicon energy band gap, thereby suggesting a generation-recombination mechanism prevailing in the depletion region of the Si substrate through bulk traps. The interface traps were calculated using the high frequency method and observed to be higher for the polycrystalline films than for the highly oriented thin films. Dc leakage current studies were done in the accumulation region and both the highly oriented and polycrystalline thin films obeyed a bulk limited Poole-Frenkel type conduction mechanism. Finally, the electrical characteristics were correlated to the microstructure of zirconium titanate thin films.