The structural, thermoelectric and photoconductive properties of sulfur doped In2O3 thin films prepared by spray pyrolysis

Abstract

In this study In2O3 and In2O3:S thin films were prepared on glass substrates using the spray pyrolysis technique. The effect of sulfur impurities on the structural, morphological, electrical, thermo-electrical, optical and photoconductive properties of films has been investigated. The sulfur to indium atomic ratios (x = [S]/[In]) were varied from 0 to 15 in the spray solution. From the x-ray diffraction analysis, a phase transition occurred from the cubic In2O3 to the cubic β-In2S3 phase with increasing S-doping level. SEM images indicated that the nanostructure of the films has a particle-cluster type growth. The Hall effect measurements have shown n-type conductivity in all of the deposited films. The lowest resistance of 19 kΩ sq−1 and the highest carrier concentration of 1.32 × 1019 cm−3 were obtained for the film deposited with an [S]/[In] atomic ratio of 0.6. The maximum of the Seebeck coefficient equal to 141 μV K−1 was obtained at 400 K for the film deposited with an [S]/[In] atomic ratio of 1. The average transmittance of films varied over the range 40–80% with S-concentration. The band gap values of samples were obtained in the range of 3.85–3.96 eV. From the photoconductivity studies, the sample prepared with the [S]/[In] atomic ratio of 0.2 exhibited the highest photoconductivity among the In2O3:S films.