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

While most semiconductor devices are susceptible to radiation damage, we report here observations of an enhancement of the conductivity of undoped composite hydrogenated amorphous silicon thin films containing silicon nanocrystalline inclusions (a/nc-Si:H) following irradiation with high-energy protons. A series of films with varying nc content, synthesized in a unique dual-chamber co-deposition system, were irradiated with 16 MeV protons from a superconducting linear accelerator for fluences ranging from 2 x 10^13 cm^-2 to 10^15 cm^-2. For the highest irradiation doses, the dark conductivity is enhanced by over an order of magnitude. Unlike the persistent photoconductivity effect observed in amorphous semiconductors, the radiation-induced enhancement is permanent and is not removed by annealing, remaining unchanged at least eight months after irradiation. Various mechanisms are tested to explain the irradiation-induced conductivity enhancement, but none are found to be able to fully account for our observations.