Field and temperature effects on the electronic mobility in Alq3 structures

Tris(8-hydroxyquinoline) aluminium (Alq3) inserted in the structure ITO/Alq3/Al is used to show how dielectric spectroscopy and a $\log \varepsilon '' ={\rm f}(\log \omega)$ representation can separate dielectric conductivity by bound charges from $\gamma _{0 }$ conductivity due to residual pseudo free charges. Coupled with the I(V) characteristic, the $\log \varepsilon '' ={\rm f}(\log \omega)$ representation allow to study the mobility of these carriers as a function of the applied bias voltage V; then the mobility was estimated to be $\mu \approx 2 \times 10^{-6}$ cm2 V−1 s−1 (with V = 0), and we demonstrate that $\mu $ approximately follows a Poole-Frenkel like law. Consequently, these results show that mobility determined by field effects is generally overestimated by around one order of magnitude for an electric field at around 1 MV cm−1. More precisely, we demonstrate that pseudo free charges exhibit a field and weakly temperature dependent mobility, which is in contrast to carriers involved in the trap–charge limited current regime which exhibit a temperature dependent and field independent mobility