Determination and analysis of optical constants for thermally evaporated PbSe thin films

PbSe films have been deposited on glass and quartz substrates at room temperature by thermal evaporation technique. X-ray diffraction patterns of the obtained films showed that they have polycrystalline texture and exhibit cubic FCC structure. The optical constants, the refractive index n and absorption index k were calculated in the spectral range of 400-4000 nm from transmittance and reflectance data using Murmann’s exact equations. Both n and k are practically independent on the film thickness in the range 28 nm to 210 nm. From the analysis of absorption index data, an indirect allowed energy gap of 0.16 eV and direct allowed energy gap of 0.277 eV were obtained. Other direct allowed optical transitions were obtained with energy gap of 0.49 eV and may be due to the splitting of valence band at the Γ point due to the effect of spin-orbit interaction.