Optical properties of thermally evaporated Bi2Te3 thin films

Bismuth telluride (Bi2Te3) films were formed by vacuum evaporation on to well-cleaned glass substrates. Multiple beam interferometer was employed to measure the thickness of the samples. The structure of the sample is analyzed by X-ray diffraction technique and is found to be crystalline. The d-spacing and the lattice parameters of the samples were calculated. The structural parameters were discussed on the basis of annealing effect and on the film thickness. Optical behavior of the film samples was analyzed by obtaining their transmission spectra, in the wavelength range of 400-800 nm. The transmission is found to decrease with increase in film thickness. The transmittance falls steeply with decreasing wavelength, indicating that the films are having considerable absorption throughout the visible region. The optical constants were estimated and the results are discussed. Optical band gap energy decreases as the film thickness increases.