Cooperative effects in molecular conduction II: The semiconductor-metal molecular junction.

Our recent calculation of the effect of intermolecular interactions on molecular conduction (J. Comput. Theor. Nanosci. 2008, 5, 535) is generalized to molecules adsorbed on a model semiconductor surface and in a metal-molecule-semiconductor junction. The metal and semiconductor electrodes are represented by cubic lattices within generic tight binding models, where the semiconductor two-band structure is described by using a simple site-alteration property. A physically motivated choice of parameters for the molecule(s) and the electrodes completes the model definition. The model encompasses direct intermolecular interactions as well as through-metal interactions and can be solved exactly to yield spectral properties (surface density of states) and transport characteristics (transmission coefficients and current-voltage behavior) for single-molecule junctions and molecular layers. The model is applied to analyzing the effect of intermolecular interactions on the predicted negative differential resistance in metal-molecule-semiconductor junctions (recently observed in scanning tunneling microscopy studies of adsorbates on Si(100)).