Growth of ferroelectric Li-doped ZnO thin films for metal-ferroelectric-semiconductor FET

A metal-ferroelectric-semiconductor structure has been developed by depositing Li-doped ZnO thin films (Zn1-xLixO, x = 0.25) on p-type Si substrates by the pulsed laser ablation technique. (002) preferential oriented films were deposited at a low growth temperature of 500 deg C and 100 mTorr oxygen partial pressure. The dielectric response of the films has been studied over a temperature range 250-373 K. A dielectric anomaly was observed at 360 K. The capacitance-voltage characteristics of Ag/Zn0.75Li0.25O/Si exhibited clockwise hysteresis loops with a memory window of 2 V. The films deposited at 100 mTorr pressure show a stable current density and a saturated polarization hysteresis loop with a remanent polarization of 0.09 muC cm-2 and coercive field of 25 kV cm-1. Leakage current measurements were done at elevated temperatures to provide evidence of the conduction mechanism present in these films. Ohmic behaviour was observed at low voltage, while higher voltages induced a bulk space charge. The optical properties of Zn0.75Li0.25O thin films were studied in the wavelength range 300-900 nm. The appearance of ferroelectric nature in Li-doped ZnO films adds an additional dimension to its applications.