A scanning Kelvin probe study of charge trapping in zone-cast pentacene thin film transistors

We have used scanning Kelvin probe microscopy (SKPM) as a local probe to study charge trapping in zone-cast pentacene field effect transistors on both SiO(2) and benzocyclobutene (BCB) substrates. Annealing at 130 degrees C was found to reduce the threshold voltage, susceptibility to negative gate bias stress and trapping of positive charges within single pentacene grains. We conclude that oxygen is able to penetrate and disassociatively incorporate into crystalline pentacene, chemically creating electrically active defect states. Screening of a positive gate bias caused by electron injection from Au into pentacene was directly observed with SKPM. The rate of screening was found to change significantly after annealing of the film and depended on the choice of gate dielectric.