Influence of doping on structural and optical properties of Bi₂Te₃ thin films

The structural and optical properties of Se doped Bi₂Te_{3 - x}Se_x (0 ≤ x ≤ 0.3) and Fe doped Bi_{2 - y}Fe_yTe₃ (0 ≤ y ≤ 0.3) films, deposited by electron beam deposition technique at moderate substrate temperature, have been analyzed for two film thicknesses. The structural properties, analyzed by X-ray diffraction data, indicate the polycrystalline nature of the films with rhombohedral structure. Changes in the structural parameters have been estimated in terms of the lattice constant as function of Se and Fe concentration. The grain size is found to be in the range of 76-130 nm. The optical properties have been characterized by transmittance and reflectance measurements in the wavelength range of 400-1000 nm. The optical constants, refractive index (n) and extinction coefficient (k), have been calculated. Moreover, the variations in refractive index and extinction coefficient have been analyzed and reported for different Se and Fe doping concentration of the film of 100 nm and 150 nm thickness along with the variation in the real (ε_r) and imaginary (ε_i) parts of the dielectric constants, in the visible to ultra-violet range of wavelengths.