Effect of the distance between cathode and substrate on structural and optical properties of zinc oxide thin films deposited by RF sputtering technique

Zinc oxide (ZnO) thin films have been fabricated over glass substrates via Radio Frequency (RF) sputtering technique with varying distances between cathode and substrate. The aim of the fabrication of thin films was to study the structural, morphological, compositional, and optical properties by varying the distance between cathode and substrate. X-Ray Diffractometer (XRD) has been used to discuss the structural property of deposited thin films. The XRD patterns of fabricated ZnO thin films indicate wurtzite hexagonal crystal phase at miller indices (002) by a high intense peak at the Bragg's angle 34.4o . Crystallite size of fabricated ZnO thin films decreases from 32 nm to 17 nm with increasing the distance between cathode and substrate from 65 nm to 125 nm respectively, which have been calculated using XRD (002) peak. The information about morphological characteristics of the surface of ZnO thin films has been discussed by using Atomic Force Microscope. Some information about the bonding of fabricated ZnO thin films has been studied by Fourier Transform Infrared Spectroscopy. UV-VIS spectrophotometer has been used to investigate the optical property and Urbach parameter of the deposited ZnO thin films. Optical energy, which is also known as bandgap energy, increases from 3.16 eV to 3.25 eV with increasing the distance between cathode and substrate from 65 nm to 125 nm respectively. Urbach energy i.e., defect density decreases from 195 meV to 182 meV with the increasing the distance between cathode and substrate from 65 nm to 125 nm respectively. The change in optical transmittance, optical band gap energy, and Urbach energy has been discussed in terms of nanostructure ZnO thin films