Effect of preheating temperature on structural and optical properties of ZnO thin films by sol-gel process

ZnO thin films are prepared on glass substrate by sol-gel spin-coating method and the effect of preheating temperature on c-axis preferred orientation and optical properties of the films are investigated. The ZnO thin film that was preheated at 275 °C and post-heated at 650 °C using a sol with Zn concentration of 0.7 mol/l is highly oriented along the (002) plane. The transmittances of ZnO thin films preheated at 200∼300 °C and post-heated at 650 °C are over 85% in visible range and exhibit absorption edges at about 368 nm. The optical band gap energy is evaluated to be 3.24∼3.26 eV. The photoluminescence shows the ultraviolet emission at near band edge and broad green-yellow radiation at 490∼620 nm. The effect of preheating temperature on structural and optical properties of ZnO thin films is discussed.