Photo-stimulated discharge of highly insulating polymers (PTFE and PETP)

Photo-stimulated discharge (PSD) spectroscopy of polytetrafluoroethylene (PTFE) and polyethylene terephthalate (PETP) films volume- and surface-charged by either corona discharge or a monoenergetic electron beam was performed in order to investigate the mechanism(s) of charge storage and to determine trap depths. The samples were irradiated with monochromatic light from a Xenon arc lamp (photon energies of 3 - 6.2 eV) at constant temperature. Experimental results indicate that the threshold energy for the generation of a photocurrent depends on factors like film material, contact between sample and electrodes, and electrode material. Space-charge profiles determined with the piezoelectrically generated pressure-step (PPS) method show quantitative depopulation of near-surface charges. Partial detrapping of volume charge was also observed. Experimental results indicate that apparent detrapping can sometimes be attributed to photo-injection and exciton generation with subsequent charge compensation.