Imperfections in amorphous chalcogenides. II. Detection and structure determination of neutral defects in As-S, Ge-S, and Ge-As-S glasses

Structure and formation processes of neutral defects in Ge-S, As-S, and Ge-As-S glasses have been investigated by ESR spectroscopy. For the Ge-S system, a well-known paramagnetic defect species showing a single absorption at g{}2.01 was reexamined by detecting and analyzing ⁷³Ge (I=9/2) hyperfine structure (hfs). The structure of the Ge-associated defect was estimated from the spin density measurement on a germanium atom (0.28) to be a germanium atom with three neighboring sulfur atoms in which the unpaired electron occupies a nonbonding sp³-like orbital. The first observation of the formation of arsenic-associated paramagnetic defect in an as-prepared glass has been accomplished by selecting the Ge-As-S system. The spin density on the arsenic 4p orbital was calculated to be about 1.00 from the detection and analysis of hfs due to ⁷⁵As. The structure of the As-associated defect was estimated to be arsenic with two neighboring sulfur atoms in which the unpaired electron occupies the nearly isolated 4p orbital of arsenic. From an observation of formation of neutral defects in the pseudobinary system As₂{S}₃$:${Ge}₂S₃, the formation process of neutral defects was proposed on the basis of the nature of chemical bonds involved in the system. The importance of the ``weak'' intermolecular force was stressed as the definitive factor for the defect formation, especially in the ``kinetic'' process of solidification.