Influence of Te substitution on optical and electrical characteristics of Te-Se-Ga-Ge chalcogenide glasses

Abstract

In this research, an attempt is made to investigate the effect of the incorporation of Te on the structural, physical, optical, and electrical properties of TeₓSe_(60−x)Ge₁₅Ga₂₅ quaternary chalcogenide glasses by employing the melt quenching technique. The glassy nature of all the glasses is verified by employing an X-ray diffraction technique. The introduction of Te in the glass network was seen to have a significant effect on the glass structure due to the larger atomic size and higher polarizability of Te compared to Se. This results in an increase in experimental density from 5.21 to 5.59 g/cm³, as well as an increase in molar and free volumes. From the optical studies, it is clear that there is a systematic change in the absorption edge towards the higher wavelength side with an increase in Te concentration in glasses, and there is an increase in Urbach energy and a decrease in optical band gap, showing more disorder in crystal structure. This is in agreement with the CBA model, where there is a decrease in cohesive energy with a decrease in bond strength due to replacement of Te-Se bonds by Se-Se bonds. The electrical measurements verify the thermal activation of electrical conduction. It is found that DC conductivity is enhanced with an increase in concentration of Te, while activation energy is reduced from 0.51 to 0.25 eV. Both the Mott and Greaves models of variable range hopping show an increase in localized states and a reduction in hopping distance. It is found that AC conductivity is in accordance with the universal power law of Jonscher, and data fit the correlated barrier hopping model with a reduction in barrier height from 1.04 to 0.65 eV. The scaling analysis confirms the universality of the electrical conduction process, irrespective of temperature and composition. The electrical conductivity and carrier mobility improve with Te substitution, making the glasses good candidates for optoelectronic and infrared optical devices.