Role of the hydrogen in the light-induced defects in undoped hydrogenated amorphous silicon

We have investigated the effect of the deposition temperature (i.e. the hydrogen content) on the light-induced effects in undoped hydrogenated amorphous silicon (a-Si:H). Combined junction capacitance-temperature (C-T), ESR and IR absorption measurements are carried out in both the dark annealed state (A) and the saturated light-soaked state (B), as well as after partial annealing of the samples, starting from state B. The experimental results indicate that the films deposited at the highest substrate temperature (i.e. the lowest H content) exhibit a completely different behaviour from those deposited at lower substrate temperature (i.e. with higher H concentration), when the samples are left for long times at room temperature in the dark after partial annealing. These results are discussed in detail in relation to the different models proposed to explain the light-induced effects in a-Si:H.