ASYMMETRIC DEGRADATION OF ELECTRON AND HOLE MU-TAU-PRODUCTS IN A-SI-H/A-SIC-H MULTILAYERS UNDER ILLUMINATION

In a series of a-Si:H/a-SiC:H multilayers with different well layer thicknesses d(Si) we have determined the electron and hole transport properties before and after a 24 hour exposure to AM1 light. Both the well layer thickness dependence in the initial state and the degradation behaviour show an asymmetry between electrons and holes. For the annealed samples the mu-tau-product of electrons, (mu-tau)e decreases rapidly with decreasing d(Si) whereas (mu-tau)h (derived from the steady-state photocarrier grating method) changes only slightly. During light soaking (mu-tau)e changes little for small d(Si), whereas for (mu-tau)h this is true for large d(Si). A qualitative explanation is given by the analytical dependence of (mu-tau)e and (mu-tau)h on the density of dangling bond defects. Since the samples cover a large range of sublayer thicknesses we can estimate the degradation of bulk and interface regions separately.