Proton radiation-induced enhancement of the dark conductivity of composite amorphous/nanocrystalline silicon thin films

While most semiconductor materials are susceptible to radiation damage, we report here an observation of enhancements in the conductivity of undoped composite amorphous/nanocrystalline silicon thin films after irradiation with high-energy protons. When a series of films for which the nanocrystal concentration is varied were irradiated with 16-MeV protons with fluences from 2×1013 to 1015protons/cm2, the dark conductivity following irradiation is increased by up to a factor of 10. Unlike the persistent photoconductivity effect observed in amorphous semiconductors, this enhancement is permanent and is not removed by annealing. Various mechanisms are tested to explain this effect, but none are able to fully account for our observations.