Photoinduced polarization investigations in 75 MeV oxygen ion irradiated kapton-H polyimide

The photoinduced polarization in 75 MeV oxygen ion irradiated (fluence: 1.8 × 1011, 1.8 × 1012 and 1.8 × 1013 ions/cm2) kapton-H polyimide has been investigated by analyzing charge decay characteristics for different polarizing parameters viz. electric fields (40 to 600 kV/cm), temperature (40 to 250 °C) and illumination intensity (1200 to 2800 1x). The fields induced as well as thermal ionization of excitons under illumination are the main causes which provide photopolarization. The charge decay spectra reveal the presence of both shallow and deep trapping sites in pristine and irradiated kapton-H polyimide. The variation in the photopolarization with fluence shows the occurrence of secondary radiation induced crystallinity (SRIC). The SRIC is also responsible for the increase in initial current (I0P) with intensity of illumination in low fluence irradiated samples. A decrease in I0P with intensity of illumination in high fluence irradiated samples has been associated to the conversion of trapping sites into recombination centers.