Structural, Electrical, and Thermo-electric Characterization of Lightly Zn- doped PbS Films for NH3-gas Sensing

The lightly Zn-doped (PbS)1-x (Zn)x with x=0, 0.03, and 0.05 wt.% in thin film form were produced by thermal vacuum evaporation. The structural, morphological, and elemental composition of the thin films has been analyzed using XRD, SEM, and EDXS, respectively. The electrical conductivity and Seebeck coefficient of (PbS)1-x (Zn)x film of 200 nm thick were determined and discussed. Thin films' electrical conductivity increased with temperature and film thickness. Pure PbS films manifested a positive Seebeck coefficient value indicating a P-type semiconducting behavior. The appearance of negative S values in Zn: PbS films could be assigned to the increase in electron concentration provided by Zn-doping and refers to the change of the conduction to n-type one. Pure films possess a high majority carrier concentration of 8.07×1018 Cm-3. Zinc-metal-doped lead sulfide thin films were tested as NH3 gas sensors with 150 ppm of target gas concentration. The sensitivity of the PbS sensor to NH3 gas was determined at various gas concentrations ranging from 50 to 150 ppm. The gas sensitivity increased as concentrations increased. The best-attained results of 93% and 174s & 310s for sensitivity and response & recovery times respectively, were obtained by (PbS)0.95 (Zn)0.05 at RT.