Investigation of Hetero-and Homo-charges in Pristine and Iodine Doped Polymethylmethacrylate

Open circuit thermally stimulated current (TSC) and surface charge decay measurements have been carried out on the 30 urn thickness samples of pristine and iodine doped polymethylmethacrylate (PMMA) to understand the nature of decaying charge. The samples are thermally charged at different temperatures with different polarizing fields. Both types of charges, hetero-and homo-charges are present in iodine doped PMMA samples, however, only hetero-charges are observed in pristine PMMA samples. A double charge reversal from hetero-to homo-charges and homo-to hetero-charges is observed in few cases of iodine doped PMMA samples. A single anomalous TSC peak is appeared in iodine doped PMMA when polarized at high field and temperature. The appearance of anomalous current in the high temperature region is in agreement with the double charge reversals (i.e., hetero-to homo-charges and homo-to hetero-charges) observed in surface charge decay study and TSC rneasurments. This could be explained on the basis of high return rate of the charge carriers released from the traps. However, this behaviour of TSC is inherent in pristine PMMA samples. The observed behaviour of surface charge decay and TSC have been explained in terms of the existence of hetero-charge due to dipole orientation and ionic space charge drift, together with an injection of charge carriers from an electrode and subsequent localization in surface and bulk trap.