UV sensitive pulsed laser deposited ZnO thin films: Influence of growth temperature

Abstract

The thin films of zinc oxide (ZnO) were grown on sapphire (0 0 1) substrates using pulsed laser deposition (PLD) in O2 gas ambient and at different growth (substrate) temperatures (200, 300, 400, 500 and 600 °C). The effect of growth temperature on the crystallographic and morphological and photoluminescence properties of the films were investigated using X-ray diffractometer (XRD), field emission scanning electron microscopy (FE-SEM) and photoluminescence spectrometer. All the films reveal a wurtzite ZnO structure. The XRD results are well supported by the surface morphological and photoluminescence studies. The film characteristics were interrelated to their ultraviolet (UV) photo-sensing properties. The UV photodetection properties of the films were investigated at room temperature in metal–semiconductor–metal (MSM) planar configurations and are observed to be strongly driven by the growth temperature dependent crystallographic properties. The dark-current and the photocurrent of the ZnO film-based UV photodetectors are relational to the crystallite/grain size and the quality of ZnO thin films. For the photodetector based on ZnO film with a greater crystallite size, a lower dark current, and a higher photocurrent were achieved under 5 V bias voltage. The time-dependent photoresponse investigations illustrate a highly stable and fast switching UV photoresponse for the photodetector with ZnO film grown at 400°C growth temperature, which exhibits the maximum responsivity of ∼21.65 mA/W upon 2 mW/cm2 UV light exposure (365 nm), at a bias voltage of 5 V.