The effect of the substrate on transient photodarkening in stabilized amorphous selenium

The photodarkening (PD) effect has been studied experimentally for amorphous selenium (a-Se) layers with 0.2 wt.% of arsenic (As) deposited on different substrates: glass, indium tin oxide (ITO) coated glass and polyimide-coated ITO glass. It was found that the presence of As qualitatively affects the behavior of PD: while in pure (no As) a-Se the relaxation of the PD is a fast process characterized by a short (∼ 10 s) time constant, in As-containing a-Se it has both short (same as in pure a-Se) and comparably long (∼ 80 s) components. The interface between a-Se and the substrate affects the PD qualitatively: it influences the magnitude of the effect while not changing the kinetics of the process. The buildup of the PD was more pronounced for the glass substrate (the most rigid) and was least pronounced for the polyimide-coated ITO glass (the most flexible). The difference can be attributed to a different strain at the interface.