Pretreating temperature controls on structural, morphological and optical properties of sol–gel ZnO thin films

ZnO thin films on glass substrates were synthesised by sol-gel method with different pretreating temperature. The thermal behaviours of dried gel were firstly tested and found the relationship between organics evaporation and pretreating temperature. Then the structural, morphological and optical properties of thin films were investigated. X-ray diffraction patterns showed the phase with hexagonal wurtzite structure, and the preferred orientation growth at (0 0 2) plane increased as rising pretreating temperature. Atomic force microscope was used to measure the surface morphology of films and found the wrinkle-like at low pretreating temperature. Transmittance spectra of ZnO thin films prepared at higher pretreating temperature revealed the steeper absorption edge and the larger transmittance values, and the deduced optical energy gap increased. Meanwhile, with increasing pretreating temperature, photoluminescence spectra showed the stronger ultraviolet peak and weaker visible peaks which, respectively, originated from intrinsic emission and various defect emissions.