Initial results were reported of the use of the modulated photocurrent method, in transient mode, to study deep electron trapping in amorphous hydrogenated material. The measurements showed that the distribution of such gap states shifted monotonically to shallower thermal energies when a biasing light was applied; with a rise-time of roughly 5s up to saturation at 300K. It shifted monotonically to deeper thermal energies when the light was removed, with a recovery time of some 100s. Photoconductivity transients were also recorded, in this long-time regime, under identical conditions. It was found that there existed an intimate relationship between the movement of the modulated photocurrent peak and that of the quasi Fermi-level, as deduced from the transient photoconductivity. It was concluded that the results provided direct evidence of the effects of deep-defect relaxation upon trapping dynamics and photoconductivity decay in amorphous hydrogenated material.

J.D.Cohen, F.Zhong: Journal of Non-Crystalline Solids, 1995, 190[1-2], 123-32