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 a bare glass substrate with a 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 was estimated using the Scherrer equation as much as 44.5nm. The morphology of samples showed that pebble-shaped ZnO particles were covered on the entire substrate homogeneously. The results indicated the excellent optical properties in the visible-infrared region with high absorption in the UV spectrum. The extrapolated cut-off for the transmittance spectrum was at 373nm, which confirmed the calculated optical bandgap of this sample at 3.27eV. The optical properties showed that the deposited samples are suitable substrates for the fabrication of UV detectors. Two back-to-back Schottky contacts of Au were deposited on the ZnO substrate to fabricate UV detectors, and a metal-semiconductor-metal structure was designed. The optoelectrical properties of detectors were carried out using the measurement of current-voltage curves. The results indicated a high photosensitivity of 0.32 corresponding to the high performance of the fabricated device. Moreover, the device showed a short rise time of 0.40s and recovery time of 0.45s indicating the high speed of detection for fabricated UV detectors.

Keywords:

ZnO thin films , physical properties , Thermal annealing , Ultraviolet detector , Epitaxial growth