Analysis of air and vacuum annealing on microstructural, optical and electrical characteristics of In₂O₃ layers for gas sensors

Abstract With consideration of significant potential of metal oxides in the effective gas sensing applications, herein, an assessment of air and vacuum annealing to the physical characteristics of In2O3 (Indium Oxide) layers is meticulously unveiled. Development of 550 nm thin In2O3 films on glass and ITO (Indium doped Tin oxide) coated substrates is accomplished by means of electron beam evaporation technique. An annealing treatment on grown In2O3 layers is executed at 300 °C, 375 °C and 450 °C for one hour in air and vacuum conditions followed by their subsequent characterizations using X-ray diffractometer, UV-Vis spectrophotometer, source meter, scanning electron microscope, and energy dispersive spectroscope tools. The crystallite size corresponding to predominant cubic peak (222) is obtained in 23-33 nm range for both types of films and observed least at 450 °C. Optical analysis exhibited that In2O3 films showed maximum transmittance of ~90% in visible region whereas band gap is measured within the range 2.20-3.50 eV. The electrical measurements unveiled Ohmic nature of films contacts where resistivity of In2O3 layers is found to be enhanced with air and vacuum annealing temperature. The morphological micrographs indicate uniform In2O3 films deposition with nanospherical grains and EDS patterns exhibited In and O peaks ensuring successful deposition of n-type In2O3 films with In richness and O vacancies. The gas sensor fabricated by using In2O3 films annealed in air at 450 °C is assessed for detection of H2S gas which showed gas response and response time of 1.08 and 38 seconds, respectively.