Investigating the effects of molarity concentration variation over optical band gap for ZnO based thin film

Abstract

Zinc Oxide (ZnO) is a very promising metal oxide semi conductor for applications in many fields like gas sensors, solar cells, and blue and ultraviolet optoelectronics devices. This thesis deals with the effect of molarity concentration on Zinc Oxide (ZnO) and hence gas sensing thin films which are fabricated by a low cost sol-gel spin coating method. The influence of precursor molarity concentration on structural property of ZnO thin films is characterized by X-ray diffraction (XRD) and Ultra Violet visible (UV-visible) spectroscopy. Sol concentration for ZnO thin film is varied from 0.05M to 1M. The study shows that crystallite sizes (grain sizes) vary with variation of sol concentration. The sol with higher concentration results in the increase in the crystallite size. Optimum sol molarity for the sensitivity of NOx gas comes out to be 0.1M. The highest sensitivity is 80% at optimum temperature 300°C. The minimum response time and minimum recovery time for optimum sol molarity which is 0.1M are 23 seconds and 25 seconds at optimum temperature. The energy band gap also gets affected by sol concentration. As molarity of precursor solution increases energy band gap starts to decrease. At higher solution molarity ZnO thin film starts to acquire the properties of the bulk material and hence energy band gap becomes approximate equal at higher solution molarity. By variation in energy band gap conductivity of material affected. It can be stated from energy band results that conductivity of ZnO thin film increases as energy band gap decreases as we move from lower sol concentration to higher sol concentration.