Dielectric studies of Alq3 and transport mechanisms

From dielectric measurements in the 20 Hz-1 MHz frequency range and between 150 and 320 K, we deduced a relaxation energy we attribute to the depth of traps filled with remaining electrons. The mean activation energy is around 0.20 eV, value in good agreement with previous determinations by other techniques. This value seems independent of the Alq3 sample preparation. The proof of the level existence around 0.20 eV confirms the transport mechanism scheme by way of these intermediate levels. Nevertheless, the experimental measurements are disturbed by other phenomena, in particular, by electrical contacts. The intensification by UV light of the dielectric absorption, that is to say the photodipolar effect, becomes hidden by the photoconductivity component. (C) 2002 Elsevier Science B.V. All rights reserved.