Surface microstructure, optical and electrical properties of spray pyrolyzed PbS and Zn-PbS thin films for optoelectronic applications

Lead sulphide (PbS) and zinc- doped lead sulphide (Zn-PbS) thin films were prepared by chemical spray pyrolysis on soda lime glass substrates at a temperature of 250 °C. Precursors were prepared from chemical reagents including zinc acetate, lead acetate and thiourea. The deposited films thicknesses and elemental composition were studied by Rutherford backscattering spectroscopy (RBS); the percentages of Pb and S were estimated as 40.58 % and 59.42 %, respectively, while for the Zn-doped sample, the percentages of Zn, Pb and S were respectively 4.84 %, 44.57 % and 50.59 %. Morphological studies revealed that the films were continuous and the particles were uniformly distributed across the substrate surface. AFM probe revealed nanostructured films with particles densely distributed across the substrates surfaces with incorporation of Zn²⁺. Statistical distribution of the grains over a specific projected area indicated average growth height of about 47 nm. Optical studies indicated that the transmission in visible light region of Zn-PbS thin film was superior to that of the undoped sample. Interband transition of both PbS and Zn-PbS films is directly allowed and their energy band gaps were found to be 0.43 eV and 1.45 eV, respectively. Electrical characterization showed that both films are of p-type conductivity with surface resistivity values of the order of 10⁴ Ω·cm.