Effect of field cycling on the ac and dc properties of Alq3 device

In this work, we have undertaken a study of the changes in the conductive properties of the ITO (Indium Tin Oxide)/Alq3 [aluminium–tris (8-hydroxyquinoline)]/Al device under successive electrical applied fields. Electrical fields up to 1.5 × 106 V/cm were applied and after each current–voltage measurement cycles a complete ac characterization was made. Current–voltage data reveals a space charge limited conduction trap dependent, with the exponent n in current decreasing with the successive applied electrical fields. This is accompanied by a decrease of dc resistance in the intermediate voltage region. In the high voltage region, the current–voltage curves reach to a limit. The impedance spectroscopy exhibits a Z∗ relaxation peak with the relaxation frequency shifting towards higher values with the successively applied fields. The Cole–Cole plot shows a successively approach to a Debye relaxation. Modeling with a parallel RC circuit (Rp and Cp) in series with a resistance (Rs), shows that the total device resistance decreases with the successive filed application while Cp remains quite constant. An attempt to interpret the data considering that the field induced structural changes that re-arrange the defect density profile giving a different location of energy levels and lowering the trap energy is made.