Sputter power and sputter pressure influenced structural and optical behaviour of RF sputtered nanocrystalline ZnO films

Zinc oxide thin films were deposited on p-type (100) silicon and Corning glass substrate by using RF magnetron sputtering at different sputter powers range 100200 W and sputter pressures range 28 Pa. The deposited films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscope and UV-Vis-NIR spectrophotometer. The films formed at sputter power of 100 W consists of weak (100) reflection and then sputter power increased to 150 W additional (110) reflection was present with enhancement in the intensity of (100) peak. Further increase of sputtering power to 200 W the intensity of (100) phase decreased with the presence of additional peaks of (002) and (101) of ZnO. The FTIR analysis confirms the Zn-O absorption band was located at 414 cm-1. The optical band gap of zinc oxide films decreased from 3.28 to 3.07 eV with increase of sputter power from 100 to 200 W. The maximum crystallite size of 21 nm, the root mean square roughness of 7.2 nm was found at films formed at working pressure of 5 Pa. The optical transmittance of the films increased from 88 to 96% and then decreased to 84% with increase of sputter pressure from 2 to 8 Pa.