Blue shift of optical band gap in ZnO thin ?lm grown by spin coating process

Optical band gap of ZnO thin films deposited on glass substrate by spin coating process was studied. The optical band gap of as-grown ZnO blue shifted from 3.11eV to 3.69 eV as the annealing temperature decreased from 300 to 100 °C. Also observed that there is a variation in the transmittance of ZnO thin film. X-ray diffraction measurements showed that samples deposited at 1000C, 2000C and 3000C consisted of amorphous phases without any prominent diffraction peaks. The AFM images showed that there is a decrease in the grain size, which is the evidence for the decrease in the transmittance.