Theoretical investigation of the electronic structure of theAlq3/Mg interface

Abstract

We have studied the atomic geometries and the electronic properties of the tris-(8-hydroxyquinoline)aluminum (Alq3)/Mg interface by using density functional theoretical calculations. Wehave found that the chemical bond is formed between the O atoms ofAlq3 and the substrate Mg atoms, and the stability of the interface structures depends on the number ofO–Mg bonds. In the up configurations, where two or three O–Mg chemical bonds are formed and theAlq3 molecular dipoles are oriented up to the vacuum side, the work function is decreased by as much as1.1 eV or more. The interface dipole is dominated by the orientation of the molecular dipoles ofAlq3. The interface gap state reported from experiments is ascribed to the highest occupiedmolecular orbital (HOMO) levels of the down configurations, which may coexist with thedominant up configurations.