Ultraviolet detectors based on annealed zinc oxide thin films: epitaxial growth and physical characterizations

In this report, ultraviolet (UV) detectors were fabricated based on zinc oxide thin films. The epitaxial growth of zinc oxide thin films was carried out on bare glass substrate with preferred orientation to (002) plane of wurtzite structure through radio frequency sputtering technique. The structural properties indicated a dominant peak at 2θ=34.28º which was matched with JCPDS reference card No.: 34-1451 and showed the wurtzite phase of deposited ZnO thin films. This peak showed the preferred orientation with the c-axis perpendicular to the surface. The crystallite size were estimated using Scherrer equation and was 44.5 nm. The morphology of samples showed that pebble-shaped ZnO particles were covered on the entire of substrate homogeneously. The results indicated excellent optical properties in the visible-infrared region with high absorption in UV spectrum. The extrapolated cut-off for transmittance spectrum was at 373 nm, which confirmed the calculated optical band gap of this sample at 3.27 eV. The optical properties showed that the deposited samples are suitable substrates for fabrication of UV detectors. In order to fabricate UV detectors, two back-to-back Schottky contacts of Au were deposited on ZnO substrate and a metal-semiconductor-metal structure was designed. The optoelectrical properties of detectors were carried out using measurement of current-voltage curves. The results indicated a high photosensitivity of 0.32 corresponding to the high performance of fabricated device. Moreover, the device showed a short rise time of 0.40 s and recovery time of 0.45 s indicating the high speed of detection for fabricated UV detectors.