Internal photoemission (IPE) studies were performed on molecular diodes in which the alkanedithiol [HS(CH(2))(n)SH, n = 8, 10] molecular layer is sandwiched between Au and GaAs electrodes. The results are compared to those from Au-GaAs Schottky diodes. An exponential energy dependence in the IPE yield was observed for the molecular diodes, in contrast to the quadratic energy dependence characteristic of metal-semiconductor Schottky diodes, indicating that Au is not the source of electrons in the IPE process in the molecular diodes. From the GaAs dopant density dependence, we also can rule out GaAs being the source of these electrons. Compared with the results of cluster electronic structure calculations, we suggest that IPE is probing the occupied levels of GaAs-molecular interfacial states.
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