On the lack of observable light-induced hydrogen diffusion near room temperature

A 5-day, high-intensity (9 W cm−2), red-light soak of a-Si:H at 65°C yields no detectable H diffusion in a tracer experiment. A new upper bound to the light-induced diffusion coefficient at a temperature so low that thermal diffusion is negligible is found. The null result found here is incompatible with models in which H emission from SiH bonds is proportional at all times to both the light intensity and the metastable defect creation rate. However, this result is compatible with the model proposed by Santos et al. in which both H emission and metastable defect creation are proportional to the product of the free electron and hole densities. In this model, this result implies that fewer than 500 H emissions occur per created metastable defect.