Optical properties of PbS thin films

The complex dielectric function of PbS thin films is studied by spectroscopic ellipsometry in the spectral range from 0.74 to 6.45 eV at a temperature of 293 K. The critical energies are determined to be $E_1$ = 3.53 eV and $E_2$ = 4.57 eV. For both energy regions, the best fit is attained at the critical point 2D ($m$ = 0). In addition, the Raman spectra and the optical-absorption spectra of PbS thin films are studied. From the dependence of the quantity $(\alpha h\nu)^{2}$ on the photon energy $h\nu$, the band gap is established at $E_g$ = 0.37 eV.