The effect of ultrasonic wave amplitude on the physical properties of zinc oxide (ZnO) deposited by ultrasonic spray method

Abstract

In this study, high quality zinc oxide (ZnO) thin films, with improved properties, were prepared by a cost-effective ultrasonic spray pyrolysis technique via a careful optimization of the used ultrasonic wave amplitude. The deposition process was performed on glass substrate and were subsequently annealed at 400 °C. We investigated the effect of various ultrasonic wave amplitude on the structural, surface morphology, optical and electrical properties of the obtained thin films, after varying the applied wave amplitude. Furthermore, deposited thin films were studied by means of XRD, UV–vis spectrophotometer, scanning electron microscope, and four-point probe technique. XRD analysis confirmed that obtained ZnO thin films have polycrystalline structure and a wurtzite (hexagonal) phase, with a c-axis preferred orientation (002). The crystallite size was about 23–30 nm. The SEM micrographs of the surface morphology show uniform, homogenous and dense films with granular structures. The films thicknesses were found to be dependent on the used wave amplitude; they were ranged from 184 to 423.5 nm. In addition, the optical properties of the deposited thin films reveal that the films are highly transparent in the visible region above 80%, while the value of energy band gap varies from 3.24 to 3.27 eV. The Electrical properties investigation revealed a resistivity around 10-3 Ω.cm, showing also a non negligible dependency with the wave amplitude tuning. We obtained an improvement in the carrier concentration (1.6 × 1020–3.9 × 1020 cm−3) and mobility (4.2–15 cm2/V.s) with the ultrasonic wave amplitude rising. High quality ZnO thin films with enhanced properties are in demand and have a large wide of applications in optoelectronics and solar cells.