Effect of annealing temperature on structural, optical and humidity sensing properties of indium tin oxide (ITO) thin films

Tin doped indium oxide (ITO) thin films were prepared by sol-gel spin coating method with In (NO3)center dot 3H(2)O and SnCl4 center dot 5H(2)O as indium and tin sources, respectively. The as deposited samples were annealed at various temperature such as, 300, 400, 500 and 600 degrees C for 2 h in ambient atmosphere. The grown ITO thin films are polycrystalline in nature with cubic structure of In2O3 with the space group La3 and the results are in good agreement with the standard JCPDS data (card no#06-0416). In addition crystalline size increases with increasing annealing temperature from 25 to 55 nm. Polycrystalline with uniform smooth surface was observed by SEM micrographs. The optical band gap energy was found to be decreased from 3.85 to 3.23 eV as the annealing temperature is increased from 300 to 600 degrees C. The humidity sensing performance (high sensitivity and fast response time) was significantly improved for 600 degrees C thin films samples, which is probably due to smaller energy band gap and physisorption between the water molecules and the surface of the thin films. The films were further characterized by PL and EDS analysis. The effect of temperature on humidity sensing mechanism of ITO thin films is also discussed.\