Dispersive optical constants and temperature-dependent band gap of cadmium-doped indium selenide thin films

Polycrystalline cadmium-doped indium selenide thin films were obtained by the thermal co-evaporation of alpha-In2Se3 crystals and Cd onto glass substrates kept at a temperature of 200 degrees C. The temperature dependence of the optical band gap in the temperature region of 300-450 K and the room temperature refractive index, n(lambda), of these films have been investigated. The absorption edge shifts to lower energy as temperature increases. The fundamental absorption edge corresponds to a direct energy gap that exhibits a temperature coefficient of -6.14 x 10(-4) eV K-1. The room temperature n(lambda) which was calculated from the transmittance data allowed the identification of the oscillator strength and energy, static and lattice dielectric constants and static refractive index as 20.06 and 3.07 eV, 7.43 and 10.52 and 2.74, respectively.