New type of charged defect in amorphous chalcogenides |
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Authors: | Simdyankin S I Niehaus T A Natarajan G Frauenheim Th Elliott S R |
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Institution: | Department of Chemistry, University of Cambridge, Lensfield Road, Cambridge CB2 1EW, United Kingdom. sis24@cam.ac.uk |
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Abstract: | We report on density-functional-based tight-binding simulations of a series of amorphous arsenic sulfide models. In addition to the charged coordination defects previously proposed to exist in chalcogenide glasses, a novel defect pair, As(4)](-)-S(3)](+), consisting of a fourfold coordinated arsenic site in a seesaw configuration and a threefold coordinated sulfur site in a near-planar trigonal configuration, was found in several models. The valence-alternation pairs S(3)](+)-S-1 are converted into As(4)](-)-S(3)](+) pairs under HOMO-to-LUMO electronic excitation. This structural transformation is accompanied by a decrease in the size of the HOMO-LUMO band gap, which suggests that such transformations could contribute to photodarkening in these materials. |
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