CHEMISTRY AND ELECTRONIC-PROPERTIES OF METAL-ORGANIC SEMICONDUCTOR INTERFACES - AL, TI, IN, SN, AG, AND AU ON PTCDA

The chemistry and electronic properties of interfaces formed between t hin films of the archetype molecular organic semiconductor 3, 3, 9, 10 perylenetetracarboxylic dianhydride (PTCDA) and reactive and nonreact ive metals are investigated via synchrotron radiation photoemission sp ectroscopy. In, Al, Ti, and Sn react at room temperature with the anhy dride group of the PTCDA molecule, producing heavily oxidized interfac e metal species and thick interfacial layers with a high density of st ates in the PTCDA band gap. The penetration of the reactive metal spec ies in the PTCDA film is found to be inversely related to their first ionization energy. The noble metals Ag and Au form abrupt, unreacted i nterfaces. The chemical and structural results correlate well with the electrical properties of the interfaces that show Ohmic behavior with the reactive metal contacts and blocking characteristics with the nob le metals. The Ohmic behavior of the reactive metal contacts is ascrib ed to carrier hopping and/or tunneling through the reaction-induced in terface states.