Conditions for ohmic electron injection at the Mg/Alq3 interface

Abstract

We show that the contacts formed by magnesium on tris (8-hydroxyquinoline) aluminum (Alq3) are intrinsically ohmic when they are fabricated and operated in ultrahigh vacuum. Under the same conditions, the injected current shows a steep increase approximately proportional to the seventh power of the applied voltage that we assign to trap filling. Only a subsequent contact with oxygen leads to an injection-limited behavior, where the observed steep current increase is caused by potential barriers at the contacts. In addition, we observe that electron injection in oxidized structures can be very well described by Fowler–Nordheim tunneling in the case when electrons are injected from the magnesium (Mg) contact evaporated onto Alq3.