Observation of the Mott-Gurney law in tris (8-hydroxyquinoline) aluminum films

We show that tris (8-hydroxyquinoline) aluminum (Alq(3)) thin films produced and characterized under ultrahigh vacuum conditions present a well-defined squared-law dependence of the injected current on the applied voltage at applied electric fields of the order of 0.25-1 MV/cm. From this, one derives an electric-field-independent electron mobility of the order of 10(-7) cm(2)/(V s), with a variation between different samples of about one order of magnitude. Observations of current-voltage characteristics with clear indications of trap-filling and space-charge-limited conduction at high fields in Alq(3) excludes the existence of traps with an exponential distribution of trap energies, as is commonly assumed in amorphous materials. (C) 2002 American Institute of Physics.