Fabrication and temperature-dependent band gap shrinkage of α-phase Bi₂O₃ thin films grown by atomic layer deposition method

α-Bi₂O₃ thin films were deposited on different substrates by atomic layer deposition method. The results of X-ray diffraction, high-resolution transmission electron microscopy and X-ray photoelectron spectroscope correspond to α-Bi₂O₃. The Fourier transform infrared spectroscopy analyses indicate that the reaction is rather complete during the deposition. Optical properties of the films have been investigated using ultraviolet-infrared transmittance spectra in the temperature range of 8-300 K. It is found that the band gap Eg decreases from 3.12 to 3.03 eV with the temperature. The parameters ±B and ΘB of the Bose-Einstein model are 69.3 meV and 293.9 K, respectively. The band narrowing coefficient dEg/dT is 0.435 meV/K at room temperature. The present results can be considerable for future application of Bi2O3-based electro-optic and wide temperature range optoelectronic devices.