Optical properties and critical points of PbSe nanostructured thin films

The spectroscopic ellipsometry method is used to investigate the optical properties of PbSe nanostructured thin films formed by the chemical deposition method. Function $d^{2}\varepsilon/d \omega^{2}$ formed by numerical differentiation of experimental data of the dielectric function $\varepsilon/\omega$ is used for better structural resolution of the interband transitions and the determination of critical points. Theoretical fitting is performed using the “Graphical Analysis” program. The best fit is found for the two-dimensional (2D) shape of the critical point $(m = 0)$ for the energy region $E$ = 2–3 eV, and one critical point corresponding to $E_g$ = 2.5 eV is determined. This value is attributed to the $L_4\to L_6$ transition of the Brillouin zone.