Structural and electrical properties of PbS films doped with Cr$^{3+}$ ions during chemical deposition

Evolution of the morphology, composition, structural characteristics (lattice constant, microstrains, texturing), and optical and photoelectric properties of PbS films produced by chemical deposition in the presence of ammonium iodide and chromium (III) chloride at concentrations of up to 0.02 M is studied. According to the data of elemental analysis by energy-dispersive X-ray spectroscopy, the Cr content in PbS films nonmonotonically depends on the CrCl$_3$ concentration, and the highest content is 1.08 at.%. The size distribution of particles is monomodal, and the average size of particles forming the films varies from $\sim$100 to $\sim$225 nm at a nanoparticle content of 2–6%. The introduction of NH$_4$I and CrCl$_3$ into the reactor preserves the B1 cubic structure of PbS and yields an increase in the band gap $E_g$ by 0.16–0.20 eV, a decrease in the dark resistance $R_d$, and an increase in the voltage sensitivity Us. The dependences of $E_g$ and $U_s$ on the chromium-salt concentration in the reaction bath are of extreme character, with a maximum at 0.016 M of CrCl$_3$, which is due to the nonmonotonic incorporation of chromium into the PbS lattice. The results of studies of the current–voltage characteristics of PbS(I) and PbS(I, Cr) thin-film layers are in good agreement with the data on the structural, optical, and photosensitivity properties.