Chemistry, diffusion, and electronic properties of a metal/organic semiconductor contact: In/perylenetetracarboxylic dianhydride

We present a photoemission investigation of the interface between In and 3, 4, 9, 10 perylenetetracarboxylic dianhydride (PTCDA). The interfacial region is very wide due to an anomalously fast diffusion of In into the organic layer. In also reacts with the anhydride end groups of the molecules. The absence of metal clustering, which permits diffusion, is believed to be due to the ionization of In and ion-ion repulsion in the PTCDA matrix. Finally, the ohmicity of the In/PTCDA contact is attributed to reaction-induced electronic gap states created throughout the wide interfacial region upon formation of the interface. This study provides the first direct correlation between chemistry and electronic properties of a metal contact on an organic molecular semiconductor.