Effect of film thickness and microstructure on the optical and photoconductive performance of PbS thin films prepared by chemical bath deposition

Abstract This work presents the deposition of lead sulfide (PbS) thin films on glass substrates prepared via chemical bath deposition (CBD). The influence of film thickness on surface morphology and structure is investigated. Film thicknesses (300-1200 nm) were prepared layer-by-layer. The films exhibit shiny, continuous, and homogeneous appearances. X-ray diffraction (XRD) reveals that the prepared films were polycrystalline with (200) preferred crystal orientation. Scanning Electron Microscopy (SEM) shows that the agglomeration of grains becomes bigger (increased from 90 ~ 225 nm) with film thickness. Optical transmission and reflectance were employed to study the optical properties of the films in the spectral range 200 to 2500 nm. The optical band gap of the films decreases from 1.55 eV down to 0.93 eV, corresponding to wavelengths 800 nm to 1.3 µm, as the thickness of the PbS film increases from 300 to 1200 nm. The absorption coefficient of the films varies from 10 4 to 10 5 cm -1 in the spectral range of 300 to 2500 nm. The films’ refractive indices in the 800-850 nm range are similar for film thicknesses up to 600 nm, but they show a discontinuity at 850 nm for thicker films. Photoconductive response occurs for film thicknesses of 600 nm or less. In contrast, thicker films do not respond to light.