Physical and UV photodetection properties of pulsed laser deposited Mg0.05Zn0.95O thin films: Effect of oxygen pressure

Abstract

Mg0.05Zn0.95O (or MZO) thin films have been deposited onto glass substrates by pulsed laser deposition (PLD) at 400°C under various oxygen pressures. All the films exhibit the wurtzite phase with a preferential c-axis orientation. The compact packing of the crystal grains is observed for the MZO films prepared at lower oxygen pressure. The grain size, film thickness and surface roughness are observed to be reduced with increasing oxygen pressure. The optical transmittance increases with an increase in oxygen pressure and the band gap experiences a red shift. The room temperature UV photodetection properties of MZO films were investigated in metal–semiconductor–metal (MSM) planar configurations and are found to be highly dependent on oxygen pressure. The photocurrent improves on reduction in the oxygen pressure due to enhancement in film crystallinity and oxygen vacancies. The photocurrent and responsivity were measured as a function of optical power density and applied voltage, respectively. The stability of MSM UV photodetectors was ensured by periodically switching the photoillumination on and off at regular time intervals. Highly stable and fast switching UV photoresponse characteristics are confirmed for the photodetector having MZO film prepared at 2×10−3torr oxygen pressure; which demonstrates highest responsivity of ∼0.2275A/W upon 2mW/cm2 UV exposures at 365nm at 5V bias voltages.