Formation of Schottky barriers at interfaces between metals and molecular semiconductors of p- and n-type conductances

In order to clarify electronic structures of molecular semiconductor/metal interfaces, a Schottky-Mott rule is examined for vacuum-sublimed films of two kinds of porphyrins, which have similar chemical structures, but opposite conductance types. The result shows that Schottky barrier heights are simply determined by the difference in work function between the porphyrin solids and metals irrespective of the conductance types of the porphyrin semiconductors, indicative of negligible influence of surface states on the Schottky barrier formation. Measurements of photocurrent generation efficiencies at these Schottky junctions indicate that a surface recombination process is not a major deactivation route for electron-hole pairs generated in the molecular semiconductors by light. (C) 1996 American Institute of Physics.