Structural and optical properties of lead sulfide thin films prepared by RF-sputtering technique

Abstract

In the present investigation, we explored the structural and optical properties of lead sulfide (PbS) thin films deposited on glass substrates. For this purpose, the radio frequency (RF) sputtering technique was applied and the films were studied at different substrate temperatures (25–200 °C). The crystallography and microstructure of the aforementioned films were measured utilizing x-ray diffraction (XRD) and scanning electron microscopy (SEM), and the optical properties using a UV–VIS spectrophotometer. The XRD results demonstrated that all the films are polycrystalline with an FCC crystal structure and a preferred orientation along the (111) plane. It has been found that the measured lattice constants closely match the theoretical values. The crystallite size increases with substrate temperature within the range of 100–200 °C. The optical properties of the films were studied by recording the transmittance spectrum in the range (350–1100 nm) and analyzed using the Pointwise Unconstrained Minimization Approach (PUMA) program. The films reveal a reduced transmittance with rising temperature from 25 to 150 °C. It was also observed that the refractive index (n) and extinction coefficient (κ) decrease with rising wavelength. Additionally, the absorption coefficient (α) was found to increase with higher photon energy. Using Tauc’s relationship, the optical band gap (\({E}_{g}\)) was determined. The results indicated that \({E}_{g}\) decreases with substrate temperature, the former ranging between 2.36 and 2.64 eV.