Influence of grain size on structural and optic properties of PbS thin films produced by SILAR method

• The effects of grain size on the structural, optical properties of PbS thin films deposited by SILAR were investigated.
• The preferred orientation varied from the (111) direction to the (200) direction with changing grain size.
• The energy band gaps of the thin films shift from 1.33 eV to 1.92 eV in connection with deposition conditions.
• The refractive index, extinction coefficient, real and imaginary dielectric constants varied with increasing dipping cycles.

In this the paper, we use the successive ion layer adsorption and reaction technique (SILAR) chemical deposition method to fabricate good quality PbS thin films and the effects of grain size on the structural and optical properties of the thin films were determined by varying deposition cases. All of the films obtained in different dipping cycles show cubic rock-salt (NaCl) structure. The preferred orientation changed from the (111) direction to the (200) direction with increasing dipping cycles. Grain size determined from scanning electron microscopy (SEM) increased from 32 nm to 104 nm. Moreover, changing of atomic ratio of the thin films is determined according to the results of energy dispersive X-ray (EDX). The transmission of the thin films was characterized by UV–Vis measurements from 400 nm to 1100 nm. It was determined from the allowed direct graphics that the energy band gaps of the thin films shift from 1.33 eV to 1.92 eV in connection with deposition conditions. The variation in band gap may be attributed to the variation of grain size. Additionally, the refractive index (n), extinction coefficient (k), real (ε1) and imaginary (ε2) dielectric constants varied with increasing immersion cycles.