CHEMISTRY AND ELECTRONIC-PROPERTIES OF METAL CONTACTS ON AN ORGANIC MOLECULAR SEMICONDUCTOR

This paper gives a brief review of the electronic properties of the su rface of an organic molecular semiconductor, i.e. PTCDA, and of the ch emical and electrical properties of its contacts with to metals, i.e. Ti and Au. The combination of direct and inverse photoemission spectro scopies demonstrates that correlation effects are small in PTCDA. Sync hrotron radiation photoemission spectroscopy shows that the Ti/PTCDA i nterface is reacted and that chemistry-induced electronic states in th e PTCDA band gap lead to an Ohmic contact. The Au/PTCDA interface, on the other hand, is unreacted and abrupt and the Au/PTCDA contact is re ctifyiing. This duality, which applies also to other metal/PTCDA inter faces, suggests the overwhelming importance of chemistry in defining e lectrical properties of contacts to organic molecular thin films.