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

Radiation-induced conductivity (RIC) of hydrogenated amorphous silicon (a-S i: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 (G D). Electric conductivity of the standard GD samples has an increase at the beginning of the proton irradiation, followed by a slower increase with fu rther irradiation. After stopping the irradiation, the conductivity decays but remains similar to 2 orders of magnitude greater than the conductivity of an unirradiated sample. This increased conductivity lasts for a long tim e, 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 f luence, conductivity increases with the irradiation, but the increased cond uctivity decays in times less than a second after stopping the irradiation. Photoconductivity which increased in correlation with the PEC is also pres ented. Using the new experimental results, possible mechanisms of the PEC a re discussed. (C) 2000 Elsevier Science B.V. All rights reserved.