Persistent excited conductivity and the threshold fluence in a-Si:H under 17 MeV proton irradiation

Abstract Radiation-induced conductivity (RIC) of hydrogenated amorphous silicon (a-Si:H) has been studied under 17 MeV proton irradiation. Two kinds of a-Si:H samples were fabricated by either standard- or He-diluted glow-discharge (GD). Electric conductivity of the standard GD samples has an increase at the beginning of the proton irradiation, followed by a slower increase with further irradiation. After stopping the irradiation, the conductivity decays but remains ∼2 orders of magnitude greater than the conductivity of an unirradiated sample. This increased conductivity lasts for a long time, and is labeled persistent excited conductivity (PEC). At T =200 K, the PEC is stable over 30 h. In the He-diluted GD samples, the PEC also occurs but a threshold fluence to cause the PEC is observed. Below the threshold fluence, conductivity increases with the irradiation, but the increased conductivity decays in times less than a second after stopping the irradiation. Photoconductivity which increased in correlation with the PEC is also presented. Using the new experimental results, possible mechanisms of the PEC are discussed.