Surface state charge dynamics in hydrazone-doped polyesters

Electronic properties of surface states in hydrazone-doped polyesters (HDPs) have been investigated using a series of thin-film Au/HDP/Al diode structures. Controlled space-charge-limited hole injection from the Au ohmic electrode under forward-bias was used to charge surface states in the vicinity of the Al blocking electrode. Subsequent reverse-biasing of the diodes to extract the remaining surface charge after suitable delay intervals permitted the occupation dynamics of holes trapped in the surface states to be determined. The decay times for trapped holes are found to depend upon the level of hydrazone doping in the films and also the initial trap occupancy following forward-bias charging. A simple surface-leakage model in which the leakage mobility is dependent upon the local surface electric field is found to provide a good description of the experimental data. The leakage model suggests that the minimum density of surface states is 4 x 10(12) cm(-2) and that these states lie within about 17 of the film surface.