Electric conduction of electroluminescent metal chelate thin films

Electric conduction in vacuum-deposited films of electroluminescent metal-chelates, tris-(8-hydroxyquinoline) aluminum (Alq3) and zinc bis-(2-(o-hydroxypheyl)-benzoxazolate)) (ZnPBO), were studied by current (I)-voltage (V) measurement. The I-V characteristics demonstrated that the films exhibited trap-controlled conduction. For the Alq3 film, conductivity sigma was estimated to be 3.0 x 10(-15) Scm(-1) from the characteristic in ohmic current region. From the I-V characteristic in space charge limited current region, further, carrier mobility mu of the Alq3 film was estimated to be 5.0 x 10(-7) cm(2)V(-1)s(-1): this value is in good agreement with electron mobility evaluated by the time-of-fight technique. For ZnPBO, the values of sigma and mu were estimated to be 2.0 x 10(-14) Scm(-1) and 7.0 x 10(-6) cm(2)V(-1)s(-1), respectively.