Magnetic properties for metastable negative- U defects in amorphous semiconductors

Abstract

Optically induced metastable centers are studied in As 2S 3 chalcogenide glasses using the magnetic susceptibility technique for 3.5≤ T≤300 K. The temperature dependencies of the magnetic susceptibility ( χ) exhibit spin instability of both a hole center localized at a nonbonding lone pair chalcogen orbital and an electron center formed by an As p-orbital. The χ fatigue at low temperatures is shown to result from the negative- U dissociation of paramagnetic states 2D 0→D −+D + that causes also the absence of an ESR signal before illumination. Irradiation with light whose energy corresponds to the Urbach tail of the absorption edge is found to result in a growing χ signal that is due to optically induced paramagnetic states revealed also by the EPR signals: D −+D ++ hν→2D 0, whereas subsequent irradiation with infrared light in the mid-gap bleaches both the optically induced magnetic susceptibility and ESR signal to its cold dark efficiency. Metastable properties for paramagnetic states located in the gap of As 2S 3 are discussed in the framework of the negative- U reaction that is accompanied by the restoration of the PL and the fatigue of the ESR signals and the magnetic susceptibility value.