EFFECT OF THE DANGLING-BOND CHARGE ON THE AMBIPOLAR DIFFUSION LENGTH IN A-SI-H

The light intensity dependence of the photoconductivity (sigma-ph), of the ambipolar diffusion length (L(amb)) and of the ratio of the effective mobilities (b = mu-n*/mu-p*) has been measured on undoped a-Si:H. L(amb) and b have been measured using the steady-state photocarrier grating (SSPG) method. The kinetics of the light-induced degradation (Staebler-Wronski effect) of a typical undoped hydrogenated amorphous silicon (a-Si:H) film is presented: it illustrates that the measured value of L(amb) varies in a quite different manner with deep defect density that, sigma-ph. All these results can be explained by incorporating the effect of the dangling-bond charge into the model (used hitherto), that included only the effect of the charge trapped in the bandtails.