In order to clarify the microscopic origin of the photodegradation in a-Si:II, two kinds of approaches have been done. One approach is to carry out the light soaking both at room temperature (RT) and 77 K to cause the photodegradation and to investigate the recovery by thermal annealing. The other approach is to investigate the light-induced ESR in hydrogenated amorphous silicon-nitrogen alloys (a-Si1-xNx:H) and to see the x-dependence down to x = 0. From the first approach, it is found that there is a very broad continuous distribution of annealing activation energies from a few eV through 1.4 eV. It appears less likely that such a wide distribution of annealing activation energy is related with the bond-breaking model. On the other hand, it is found from the second approach that there exist two distinct origins for the light-induced spins, the fast process and the slow process, which are likely to be the carrier capture and the bond breaking, respectively. From the continuation of the observed behavior to a-Si:H, that is, x = 0 in a-Si1-x
Nx:H, the RT photodegradation in a-Si:H appears to be the bond breaking.