Comparison of ZnO thin films on different substrates obtained by sol-gel process and deposited by spin-coating technique

Abstract

In the present paper, zinc oxide thin films obtained by sol gel process and deposited on glass, sapphire, Si (100), Si (111) and ZnO substrates by spin-coating technique have been studied. Effects of using different substrates on the structural, morphological and optical properties have been investigated. The structural properties have been analyzed using X-ray diffraction (XRD) and the recorded patterns indicated that all the deposited films are polycrystalline with a hexagonal Wurtzite structure and exhibit preferentially oriented along the c-axis direction. The surface morphology has been examined by Scanning Electron Microscopy which revealed that the microstructure of the films strongly affected by the nature and orientation of substrate namely grain shape and size. Optical absorbance measurements have been taken using UV-Vis spectrophotometer and the calculated values of the direct band gap energy are around 3, 3.08 and 3.19 eV, for the ZnO films deposited on ZnO, sapphire c and glass substrates, respectively. Photoluminescence measurements taken at 4 K exhibit a near band edge composed by two principal’s peaks situated at 3.36 and 3.31 eV and attributed to the neutral donor bound exciton (D°X) and to the deep acceptor (A°X), their intensity varied with the nature of substrate.