Optical Properties of Thermally Deposited Bismuth Telluride in the Wavelength Range of 2.5-10 µm

The optical constants (the refractive index n, the absorption index k and the absorption coefficient α) of Bi$\text{}_{2}$Te$\text{}_{3}$ thin films were determined in the wave-lenght range of 2.5 to 10 µm. The shape of the absorption edge in Bi$\text{}_{2}$Te$\text{}_{3}$ thin films has been determined from transmittance and reflectance measurements. The edge is of the form expected for direct transition corresponding to E$\text{}_{g}$ = 0.21 eV. The optical constants were used to determine the high frequency dielectric constant ε$\text{}_{0}$ = 58, the optical conductivity σ =σ$\text{}_{1}$ + σ$\text{}_{2}$ as well as the volume and surface energy loss functions. All these parameters were used to get some information about the intraband and interband transitions.