Effect of heat treatment on characteristics of nanocrystalline ZnO films by electron beam evaporation

Zinc oxide thin films have been grown on glass substrate at room temperature by electron beam evaporation and then were annealed in annealing pressure 600 mbar at different temperatures ranging from 250 to 550 °C for 30 min. Electrical, optical and structural properties of thin films such as electrical resistivity, optical transmittance, band gap and grain size have been obtained as a function of annealing temperature. X-ray diffraction has shown that the maximum intensity peak corresponds to the (002) predominant orientation for ZnO films annealed at various temperatures. The full width at half maximum, decreases after annealing treatment which proves the crystal quality improvement. Scanning electron microscopy images show that the grain size becomes larger by increasing annealing temperature and this result agrees with the X-ray diffraction analysis. ► Conductance of ZnO films decreases with increasing annealing temperature. ► Optical transmittance increase by heat treatment and at 550 °C, reach to %95. ► XRD patterns show that ZnO films crystallization improved with annealing treatment. ► Band gaps in ZnO films change from 3.26 eV to 3.29 eV by annealing treatment. ► Annealing has an important role in controlling characteristics of ZnO films.