Time-of-Flight Photocurrents in Amorphous Semiconductors under Nonequilibrium Trap States

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Abstract
Characteristic changes in time-of-flight photocurrents induced with photoelectric bias excitation have been studied in amorphous \asse, Se and Si:H films. If \asse films are exposed to bias illumination under electric fields, the transit time of dispersive carriers increases by a factor of ∼2. In Se and Si:H films, bias excitation makes nondispersive photocurrent signals featureless. In all the materials, bias excitation increases the number of collected carriers. These effects observed in photoelectrically biased amorphous semiconductors have been analyzed on the basis of a multiple-trapping model. The result suggests that bias excitation yields two effects: a density increase in shallow trap states and a modification of electric fields.