Structural, optical, and photosensitive properties of PbS films deposited in the presence of CaCl$_{2}$

Polycrystalline lead-sulfide (PbS) films doped with calcium are synthesized on sitall and glass substrates by chemical bath deposition with the use of thiocarbamide and a CaCl$_{2}$ additive at concentrations of up to 5 mM. Introduction of the CaCl$_{2}$ additive into the reaction solution greatly prolongs the induction period of the process of synthesis. The thicknesses of the PbS and PbS(Ca) films are, correspondingly, 200 and 150 nm at an average crystallite dimension of 100 nm. The maximum calcium content in the films is 0.06 at % for layers on sitall substrates and 0.11 at % for layers on glass substrates. Doping with calcium does not influence the crystal structure of lead sulfide (the cubic B 1 structure, space group $Fm3\bar m$) but brings about an increase in the crystal-lattice period from $a$ = 0.59343(2) nm to a = 0.59413(1) nm, an increase in microstrains, and partial ordering of the crystallites forming the film. Upon the introduction of calcium, the band gap decreases from $E_g$ = 0.40 eV at 295 K (0.38 eV at 90 K) to $E_g$ = 0.38 eV (0.37 eV). The introduction of up to 5 mM of CaCl$_{2}$ into the reaction mixture increases the voltage–power sensitivity of the films by a factor of $\sim$1.7, which is attributed to oxygen-containing compounds formed in the films as a result of the increase in the induction period of the process of synthesis.