Photoconducting nanocrystalline lead sulphide thin films obtained by chemical bath deposition

Abstract

A chemical bath deposition method of preparing photoconducting nanocrystalline lead sulphide (PbS) thin films at room temperature (RT) is described. The aqueous bath of lead acetate, thiourea, and ammonium hydroxide produce films of about 100 nm thicknesses in 45 minutes. X-ray diffraction (XRD) studies show that these films are nanocrystalline cubic PbS with 10 nm crystallite size. Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) revealed that the films consist of spherical grains of sizes 100 to 200 nm. The transmission spectra of the films show onset of absorption edge around 850 nm and the bandgap is around 1.65 eV. The films are p-type with dark conductivity of 2.5×10−3 S/cm and mobility of 0.07 cm2/V⋅s. The photosensitivity is 6–7 for an illumination of 80 mW/cm2 from a halogen lamp (50 W, 12 V). Transient photoconductivity measurements reveal short and long life times of minority carriers. Thermoelectric and photothermoelectric studies show that photoconductivity in these films is mainly due to photogenerated majority carriers.