HIGH-FIELD TRANSPORT IN DISORDERED MATERIALS

Recent experiments on a variety of polymeric and other disordered organic semiconductors indicate an apparent anomaly in the field dependence of the carrier mobility, anomaly in the sense that conventional high field hopping theory does not appear to account for the apparently universally observed exp{γF 1 2} law. Various explanations suggesting polaronic and Poole-Frenkel type effects have been put forward in the literature. Similar effects had been observed some years ago in low mobility dielectrics. We re-examine non-equilibrium hopping transport in the high field limit and conclude that the anomaly is due to a density of states effect. The latter may or may not include electronic correlation effects. This depends on the system and type of disorder. © 1990.