Transport Properties of Amorphous Ge20Te80-xBix Glassy Alloys

Bulk samples of Ge20Te80-xBix (x = 0, 1.5, 2.5, 5.0) glassy alloy are prepared by melt quenching technique. Differential scanning calorimetric (DSC) technique has been applied to determine the thermal properties of Te-rich Ge20Te80-xBix glassy alloys in the glass transition and crystallization regions. The glass transition temperature (Tg) as well as crystallization temperature (Tc) is found to increase with increasing Bi content. This behavior is explained on the basis of coordination number m and deviation from stoichiometry, R values. From the temperature dependent dc conductivity measurements, the activation energy (ΔE) and the pre-exponential factor (σ0) are calculated for each glassy alloy. Optical band gap is calculated using Tauc extrapolation method and is found to decrease with increase in Bi content. It has been observed that the value of ΔE is less than half of optical band gap (Eg) indicating that the Fermi level is not located near the centre of gap.