Synthesis and optical characterization of pure and Cu doped SnO2 thin films deposited by spray pyrolysis

Pure tin oxide (SnO2) and copper (Cu) doped SnO2 thin films have been deposited from tin chloride (SnCl2) and cupric nitrate Cu(NO3)(2) precursors onto glass substrates by spray pyrolysis technique at the substrate temperature of 350 square C. The doping concentration of Cu was varied from 1 to 8 wt. % while all other deposition parameters such as spray rate, carrier air gas pressure and distance between spray nozzle to substrate were kept constant. The surface morphology and optical properties of the as-deposited thin films have been studied by Scanning Electron Microscopy (SEM) attached with an EDX and UV visible spectroscopy. The transmittance for the as-deposited films was recorded in the wavelength range of 290 to 1100 nm. The optical transmission of the films was found to increase from 71 % to 80 % for initial doping of Cu up to 4% for 200 nm thickness and then decreased for higher level of copper doping. The optical band gap of undoped film was found to be 3.75 eV and it was shifted to 3.50 eV for 4 wt. % of Cu doping and then increased on further increasing the concentration of the dopants. This paper discusses the optical properties of the as-deposited SnO2 films with Cu doping.