Shimakawa et al. have observed time dependent decreasing photocurrent during exposure of light in chalcogenide thin films and explained their results in terms of photo induced metastable defect creation during illumination. for explaining their respective results Shimakawa and Elliott proposed a model,defect creation is initiated due to the formation of a self trapped exciton in the form of an intimate valence alternation pairs and these are stable at low temperature.

Yes, Dr. Shikha, Shimakawa et.al. and Shimakawa and Elliott proposed a model of defect creation which is initiated due to the formation of self trapped exciton in the form of VAPs.