Transport mechanisms in 8-tris-hydroxyquinoline aluminium (Alq3) electronic layers: a study by photodipolar absorption

André Moliton (1) , Bruno Lucas (2) , Sebastien Berthon (3) , Wassim Rammal (1) , Roger Clive Hiorns (3)

1 MINACOM
2 C2S2
3 IPREM - Institut des sciences analytiques et de physico-chimie pour l'environnement et les materiaux

This paper describes the role of traps in the electronic conductivity of 8-tris-hydroxyquinoline aluminium in a conventional sandwich structure with indium tin oxide and aluminium electrodes. New results obtained by photodipolar absorption techniques and impedance spectroscopy are presented. The former method acts as a probe to highlight the role of traps. It is shown that optical pumping of electrons to trap levels gives a clear increase in dielectric absorption due to the reorientation of dipoles associated with trapped charges. The trap depth is estimated to be around E_t= 0.19 eV, a value in good agreement with theoretical calculations and thermoluminescence measurements. The latter method permits a representation of the sample in terms of a circuit composed of a parallel capacitor (C_p) and resistor (R_p) both in series with a resistor R_s≈ 50 Ωlocated on the anode side. A logarithmic plot of R_p as a function of the dc bias voltage gives a linear law that is recognized, for the first time, to be a consequence of a trapped charge limited (TCL) current. The linearity can be improved by the introduction of a field-dependent mobility.

Mots clés: Physical Sciences

Domaines: Electronique

André Moliton, Bruno Lucas, Sebastien Berthon, Wassim Rammal, Roger Clive Hiorns. Transport mechanisms in 8-tris-hydroxyquinoline aluminium (Alq3) electronic layers: a study by photodipolar absorption. Philosophical Magazine, 2006, 86 (19), pp.2847-2863. ⟨10.1080/14786430600636351⟩. ⟨hal-01003839⟩