Temperature dependence of optical properties in Sn_0.925Mn _0.075O₂ film determined by transmittance spectra

Near-infrared-ultraviolet optical properties of Sn_0.925Mn _0.075O₂(SMO) film grown on c-plane sapphire substrate have been investigated by the transmittance spectra in the photon energy of 0.45-6.5 eV (190-2650 nm) from 5.3-300 K. The optical constants have been extracted by fitting the experimental data with the Adachi's model. The optical band gap of the film can be estimated from the relation (αE)² proportional to (hv-E_g). It is found that the absorption edge shifts to a lower energy side with increasing the temperature and the band gap E_g decreases from 3.80 to 3.72 eV. The parameters α_B and θB of the Bose-Einstein model are 45.4 meV and 221.8 K, respectively, which could be ascribed to the thermal expansion of crystal lattice and the carrier-phonon interaction. The band narrowing coefficient dE_g/dT of the SMO film is estimated to be -3.92 × 10^-4 eV/K at room temperature.