Electrical conductivity, density of states and optical band gap in Se90Te6Sn4 glassy semiconductor

Bulk Se90Te6Sn4 glassy alloy was prepared by melt quenching technique. A pellet is sandwiched between two electrodes in a closed cycle cryostat under vacuum and the resistance was measured directly, in the temperature range 175–300 K, using Keithley electrometer after applying a DC voltage of 5 V across the sample. In the temperature region (289–300 K), the experimental data of the conductivity were used to obtain the activation energy Eσ which comes out to be (0.136±0.014) eV. In the low temperature region the conductivity increases very slowly with temperature which indicates that the conduction occurs via variable range hopping (VRH) in the localized states near Fermi level. The density of localized states, N(EF) in Se90Te6Sn4 glass was calculated using Mott's model and is found to be (4.52±0.45)×1022 eV−1 cm−3. The absorption coefficient of a thin film of Se90Te6Sn4 glass is obtained from the transmission and reflection spectra. Results indicate that an allowed direct transition is involved in the prepared Se90Te6Sn4 thin film and the optical band gap equals (1.233±0.038) eV.