TRANSIENT MODULATED PHOTOCURRENT STUDIES IN HYDROGENATED AMORPHOUS-SILICON - A NEW LOOK AT DEFECT RELAXATION DYNAMICS

The first results using the modulated photocurrent (MPC) method in a transient mode to study deep electron trapping in a-Si:H are reported. The measurements show that the distribution of such gap states shifts monotonically to shallower thermal energies after bias light is applied, with a time of roughly 5 s to saturation at 300 K. It shifts monotonically to deeper thermal energies after the light is turned off, with a recovery time of roughly 100 s. The photoconductivity transients have also been recorded in this long time regime under identical conditions. It is found that there exists an intimate relation between the motion of the MPC peak and that of the quasi-Fermi level as deduced by the transient photoconductivity. These results thus provide direct evidence for the effects of deep defect relaxation on the trapping dynamics and the photoconductivity decay in a-Si:H.