Gap-state spectroscopy in amorphous selenium

Abstract

possible to locate several of the energy levels of the charged coordination defects (D+ and D-) that constitute the chalcogenide negative-U model in the amorphous selenium bandgap. However it has also been observed that the energy position of those levels is influenced by external influences such as light soaking or annealing of the samples. The post-transit time-of-flight photocurrents that reveal those energy positions have, therefore, been systematically studied in samples with different pre-histories. The optical absorption in the samples was further examined through the constant-photocurrent method (CPM), and by photothermal deflection spectroscopy (PDS). Although the TOF results provide information on the D+ and D- levels separately, while the CPM and PDS data reflect the integral optical absorption between both centres and the bands, the results do agree. The photo-induced changes that are observed are stable at room temperature.