  We investigated the electrical properties of a unipolar organic device with
traps that were intentionally inserted into a particular position in the
device. Depending on their inserted position, the traps significantly alter the
charge distribution and the resulting electric field as well as the charge
transport behavior in the device. In particular, as the traps are situated
closer to a charge-injection electrode, the band bending of a trap-containing
organic layer occurs more strongly so that it effectively imposes a higher
charge injection barrier. We propose an electrical model that fully accounts
for the observed change in the electrical properties of the device with respect
to the trap position.
