Structural and optical modification of Ga-doped zinc oxide thin films induced by thermal annealing

Ga doped ZnO (ZnO:Ga) thin films were prepared by the sol-gel spin coating technique. The films are annealed at different temperature varying from 500 degrees C to 900 degrees C in controlled oxygen environment. The effects of annealing temperature on structural, morphological and optical properties of films are investigated. The XRD results show that all deposited films are textured along the (101) direction and exhibits wurtzite phase of ZnO. The AFM images show that the grain size of ZnO films increased with increasing annealing temperature. Red shifting (band gap decreases) of the optical band gap is also observed on increasing the temperature. The observations are explained on the basis of stress and grain growth induced by thermal annealing.