Photoconduction investigations in 75 MeV oxygen ion irradiated kapton-H polyimide

摘要

Photoconduction behaviour of 75 MeV oxygen ion irradiated (Fluences: 1.8 × 10~(11), 1.8 × 10~(12)and 1.8 × 10~(13) ions/cm~2) kapton-H polyimide film in the visible region has been investigated at different temperatures ranging 400-2500 ℃ and at various electric fields ranging 40-600 kV/cm. A photoinduced exciton formation is the major source for providing charge carriers through thermolization and field-assisted dissociation processes. An attempt has been made to fit the field dependence of the steady state photocurrent to one of the several possible conduction mechanisms. In the high and low fluence (1.8 × 10~(13) and 1.8 × 10~(11) ions/cm~2) irradiated samples there exists a possibility of Poole-Frankel type of photoconduction mechanism, whereas at intermediate fluence (1.8 × 10~(12) ions/cm~2) a Schottky type photoconduction mechanism may be operative. The logI_(ps) versus 1/T plots consist of two straight lines with a knee point around 800-1000 ℃. The activation energy estimated from the slope of these lines is field dependent varying from 0.40 to 0.73 eV and 0.18 to 0.23 eV above and below the knee point, respectively. This indicates the presence of more than one type of trapping levels in irradiated kapton-H polyimide.