Investigations on structure and properties of ge-as-se chalcogenide glasses

Abstract

Germanium-Arsenic-Selenium chalcogenide glasses are considered as good candidates for photonic applications due to their excellent transparency in the infrared range and high optical nonlinearities. A deep understanding of composition-structure-property relationship in Ge-As-Se ternary system is thus becoming increasingly important, which can serve as a guideline for materials selection. In this work, the structure and various physical properties of GexAsySe100-x-y bulk glasses have been systematically investigated. Raman spectra and EXAFS measurements reveal that chemically ordered network model can be applied to Selenium-rich glasses, but fails to explain bonding characterization of Selenium-poor compositions. Atomic arrangements are more sensitive to the changes in chemical compositions. A tight association between the fragility and the deviation from stoichiometry has been found in the Ge-As-Se system by differential scanning calorimetry. It is shown that chemical compositions with the lowest values of fragility index are far less likely to incur structural relaxation. Those strong glasses are normally chosen as ideal materials for fabrication of stable photonic devices. The variation of density and elastic modulus as a function of mean coordination number both show two transition thresholds, which correlate with floppy-to-rigid phase transition and 2D-to-3D structure transition respectively. The results provide clear evidence that some physical properties of Ge-As-Se chalcogenide glasses are significantly determined by their mean coordination numbers, but could be further tuned by the chemical compositions. The detailed optical investigation shows that the generalized Miller’s rule is a simple but effective approach to estimate the nonlinearities of a broad variety of chalcogenide glasses. Nonlinear properties of these materials exhibit strong dependence upon their optical bandgap in the near infrared. It seems that the highest nonlinearity at telecommunications wavelengths is predictable in chalcogenide glasses. Show more