Coordination positron‐trapping centers in vitreous chalcogenide semiconductors

Abstract

A model of radiation-induced coordination topological defects with an associate open volume is developed in order to explain the experimental results on positron annihilation lifetime measurements in γ-irradiated vitreous chalcogenide semiconductors of the ternary As – Ge – S system. It is shown that, contrary to the native open-volume microvoids frozen technologically at thermodynamic equilibrium near a glass transition, the principally different part of void-type defects can be created as a result of 60 Co γ-irradiation. They are associated mainly with structural transformations (atomic displacements) at the medium-range ordering level in the nearest vicinity of some metastable atomic configurations, especially those containing the negatively charged coordination topological defects. 1. Introduction Vitreous chalcogenide semiconductors (VChSs) or, in other words, wide-gap semiconducting compounds of chalcogen atoms (S, Se or Te, but not O) with some elements from the IV-th and V-th groups of the Periodic Table (typically As, Ge, Sb, Bi, etc.) [1], are unique solid state materials, showing the effect of changes in their physical properties under the influence of high-energetic ionizing radiation, such as 60 Co γ-quanta with an average energy of more than 1 MeV [2, 3]. These changes are caused by specific radiation-induced structural transformations, connected with so-called coordination topological defects (CTDs) [4, 5]. These defects are created in the form of diamagnetic pairs of over- and under-coordinated atoms in a glassy-like network with positive and negative electrical charge, respectively [1, 4, 5]. The microstructural mechanism of this process is well studied in vitreous v –As2S3 [2, 3]. However, the similar transformations were not considered previously neither for v –GeS2, nor for more complicated cross-linked VChSs with two-, three- and four-fold coordinated atoms.