Effect of La doping on the structural and gas sensing properties of PbS thin films deposited by spray pyrolysis

Abstract

Abstract Phase pure PbS and lanthanum doped PbS thin films have been deposited by the spray pyrolysis technique. All the deposited films were gray to black, pin hole free and strongly adherent to the ITO glass substrates. The substrate temperature was varied between 450 and 500 °C, with doping concentration ratios of 1, 5 and 10% for La. The doping performed at 450 °C, showed phase segregation whereas successful incorporation of La in the PbS lattice was achieved at 500 °C. The films were characterized by x-ray diffraction (p-XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), Energy-dispersive X-ray spectroscopy (EDX), and ultraviolet visible spectroscopy (UV). The sensitivity of the as deposited thin films was also tested against hydrogen gas. The sensor material was exposed to a low concentration of 200 ppm of the target gas to determine the sensitivity performance of the sensor, at different temperatures while measuring the variation in the resistance. The doping of lanthanum significantly enhances the sensitivity of the PbS thin films against the target gas. The gas sensor exhibited n-type conductivity as confirmed by the decrease in resistance on exposure to hydrogen. The as prepared catalysts show good sensing behavior near room temperature and at low concentration of hydrogen at 200 ppm without the need to apply an external voltage.