We use the post-transit photocurrent in a time-of-flight experiment for spectroscopic purposes. It is shown, within the multiple-trapping framework, that the post-transit current is the Laplace transform of the density of states. A simple inversion procedure is suggested and is shown to be quite adequate provided the gap-state distribution does not vary too strongly with energy. The method has been applied to hydrogenated amorphous silicon. Experimental evidence shows that the post-transit photocurrent truly reflects the release out of deeper-lying traps and is not a consequence of nonuniform, time-dependent fields, contact-related properties, or injection phenomena. The measured ${\mu }_0$${\tau }_d$ are compatible with the deconvoluted density of states. A comparative discussion of our results with other published data obtained with conventional methods like the field-effect, space-charge-limited current, and deep-level transient spectroscopy techniques is given.

• Received 14 November 1988

DOI:https://doi.org/10.1103/PhysRevB.39.10196