Abstract
The optical constants (absorption coefficient, optical band gap, refractive index, extinction coefficient, real and imaginary parts of dielectric constants) of amorphous and thermally annealed thin films of Ga
15Se
77In
8 chalcogenide glasses with thickness 4000 Å have been investigated from absorption and reflection spectra as a function of photon energy in the wave length region 400–800 nm. Thin films of Ga
15Se
77In
8 chalcogenide glasses were thermally annealed for 2 h at three different annealing temperatures 333 K, 348 K and 363 K, which are in between the glass transition and crystallization temperature of Ga
15Se
77In
8 glasses. Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. It was found that the optical band gap decreases with increasing annealing temperature. It has been observed that the value of absorption coefficient and extinction coefficient increases while the values of refractive index decrease with increasing annealing temperature. The decrease in optical band gap is explained on the basis of the change in nature of films, from amorphous to crystalline state. The dc conductivity of amorphous and thermally annealed thin films of Ga
15Se
77In
8 chalcogenide glasses is also reported for the temperature range 298–393 K. It has been observed that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. The dc conductivity was observed to increase with the corresponding decrease in activation energy on increasing annealing temperature in the present system. These results were analyzed in terms of the Davis–Mott model.
► Thermal processes are known to be important in inducing crystallization in semiconducting chalcogenide glasses. ► Indium doped chalcogenide glasses has gained a remarkable and great interest due to its potential applications in various digital electronic devices, as digital cameras and camcorders, MP3 players, smart phones, etc. ► Analysis of the optical absorption data shows that the rule of non-direct transitions predominates. ► It was found that the optical band gap decreases with increasing annealing temperature. ► The dc conductivity were observed to increase with the corresponding decrease in activation energy on increasing annealing temperature in the present system.