Effect of Li doping on the structural, optical and formaldehyde sensing properties of In2O3 thin films

Abstract Chemical spray pyrolysis technique is utilized to deposit undoped and Li-doped indium oxide thin films on cleaned glass substrates. The effect of Li doping on the structural, optical, electrical and formaldehyde sensing characteristics on In 2 O 3 has been studied. All the thin film samples were characterized by X-ray diffraction for structural and UV–vis spectroscopy for optical analyses, respectively. The doping of Li into In 2 O 3 reduces the value of the average crystallite size and the optical transmittance in the visible region. However, a blue shift is observed in the optical band gap in the Li-doped films. The value of the direct optical band gap is found to increase from 3.35 eV in the undoped sample to 3.59 eV in the 2 at.% Li:In 2 O 3 thin film. Further, the undoped and the Li-doped films have been tested for formaldehyde vapor to check their suitability to detect the presence of the same in air. We observed that the 2 at.% Li:In 2 O 3 film exhibits the highest sensitivity for formaldehyde at a low concentration of 60 ppm and at an operating temperature of 300 °C. The sensing mechanism of formaldehyde vapor has also been presented.