Off-centered polarization and ferroelectric phase transition in Li-doped ZnO thin films grown by pulsed-laser ablation

Li-doped ZnO (Zn1-x Lix O, x=0.15) thin films have been grown on platinum-coated silicon substrates via pulsed-laser ablation. The films were grown at fixed substrate temperature of 500 °C and different partial pressure of oxygen (PO2 ∼100-300 mTorr). The films showed (002) preferred orientation. The doping concentration and built-in potential were estimated from the capacitance-voltage characteristics. In order to investigate the phase transition behavior of the films, dc conductivity and dielectric measurements were conducted. The phase transition temperature was found to be 330 K. The activation energy (dc) has been found to be 0.05 and 0.28 eV in ferroelectric and paraelectric phases, respectively. The Zn0.85 Li015 O thin films exhibited well-defined polarization hysteresis loop, with a remanent polarization of 0.2 μC cm2 and coercive field of 25 kV/cm, at room temperature. The conduction mechanism of the laser ablated Zn0.85 Li015 O films was analyzed in the light of impedance spectroscopy.