Characterization of light-erasable giant surface potential built up in evaporated Alq3 thin films

Abstract Recently high and persistent spontaneous buildup of a surface potential (SP) upon vacuum deposition of tris (8-hydroxyquinolinato) aluminum (III) (Alq 3 ), which is widely used for organic light emitting devices, on a gold substrate under dark condition (28 V for 560-nm-thick Alq 3 film) has been reported. The removal of the giant surface potential by visible light irradiation has also been reported. These properties of Alq 3 film suggest potential applications to various organic devices such as memory. In this study, we investigated the retention time of the giant potential and the mechanism of the light-induced depolarization in order to discuss the feasibility of the device applications. The observed decay rate of the surface potential in vacuum condition was roughly 10% loss in 10 years, which is enough for memory devices. As to the decay rate by light-irradiation, the observed rate was successfully reproduced by a theoretical simulation based on the photo-induced randomization of oriented Alq 3 molecules.