Electron transport in tris(8-hydroxyquinoline) aluminum (${\mathrm{A}\mathrm{l}\mathrm{q}}_3$) is investigated by impedance spectroscopy under conditions of space-charge limited conduction (SCLC). Existing SCLC models are extended to include the field dependence of the charge carrier mobility and energetically distributed trap states. The dipersive nature of electron transport is revealed by a frequency-dependent mobility with a dispersion parameter $\alpha$ in the range 0.4–0.5, independent of temperature. This indicates that positional rather than energetic disorder is the dominant mechanism for the dispersive transport of electrons in ${\mathrm{A}\mathrm{l}\mathrm{q}}_3$.

• Received 10 June 2002

DOI:https://doi.org/10.1103/PhysRevLett.89.286601