Optical and sensing properties of Fe doped ZnO nanocrystalline thin films

Undoped and Fe doped ZnO films of different molarities deposited by spray pyrolysis method using zinc nitrate and ferric chloride as precursors show polycrystalline nature and hexagonal wurtzite structure. Crystallite size decreases with an increase in dopant concentration from 0 at.% to 3 at.%. Doping improves the transmission of the films whereas it reduces the optical band gap of ZnO from 3.28 eV to 3.17 eV. The morphology resembles flake-like structures which collapse when the dopant is introduced. The samples are found to be sensitive to CO2 gas. Undoped ZnO shows maximum sensitivity at 350 degrees C for higher concentration of CO2. Doped samples show maximum sensitivity at 200 degrees C for all CO2 concentrations i.e. from 500 ppm to 4000 ppm. Maximum sensitivity is achieved at temperatures 350 degrees C, 250 degrees C, 300 degrees C and 450 degrees C for the samples prepared using precursor solution of 0.1 M molarity.