Temperature dependence of the direct allowed transitions band gap and optical constants of polycrystalline α-In2Se3 thin films

Polycrystalline α-In2Se3 thin films were obtained by the thermal evaporation of α-In2Se3 crystals onto glass substrates kept at temperature of 200 °C. The temperature dependence of the optical band gap in the temperature region of 300–480 K and the room temperature refractive index, n(λ), of these films have been investigated. The absorption edge shifts to lower energy values as temperature increases. The fundamental absorption edge corresponds to a direct allowed transitions energy gap that exhibits a temperature coefficient of − 8.51 × 10− 4 (eV/K). The room temperature n(λ) which was calculated from the transmittance data allowed the identification of the oscillator strength and energy, static dielectric constant and static refractive index as 20.7 and 2.15 eV, 10.70 and 3.26, respectively.