DEPENDENCE OF THE LIGHT-INDUCED DEGRADATION KINETICS OF PHOTOCONDUCTIVITY AND AMBIPOLAR DIFFUSION LENGTH AS A FUNCTION OF DOPING LEVEL IN A-SI-H

Variation of both photoconductivity sigma(ph) and ambipolar diffusion length L(amb) have been measured during exposure to light on a series of lightly p- and n-doped a-Si:H samples. The observed decay of the ph otoconductivity with time of exposure has been fitted by a power-law f unction. The power-law exponent observed strongly depends on doping. O n the other hand, ambipolar diffusion length generally remains constan t during the observed part of the degradation process, except for a sl ightly boron-doped sample with the Fermi-level near midgap. In the lat ter, L(amb) decreases in accordance with sigma(ph). The experimental o bservations can be qualitatively explained taking into account danglin g bonds with their three charge states(D+,D-0,D-) as main recombinatio n centers.