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There is considerable current interest in using molecular materials to influence the surface potential of semiconductor devices for nanoelectronic and sensing applications. We present experimental capacitance-voltage results showing that systematic Schottky barrier height modulation can be achieved using dipolar molecular layers in gold-molecule-silicon devices. A computational methodology that combines quantum chemistry and traditional electrostatic calculations is used to explore various physical effects that can influence barrier heights in such systems. Nonidealities such as silicon surface states can influence both the potential profile within the device and the validity of the extracted barrier height. Our devices exhibit low surface state densities, but the magnitude of surface potential modulation is modest due to molecular depolarization from the gold contact.

Metal-molecule-silicon (MMSi) devices have been fabricated, electrically characterized, and analyzed. Molecular layers were grafted to n and p+ silicon by electrochemical reduction of para-substituted aryl-diazonium salts and characterized using standard surface analysis techniques; MMSi devices were then fabricated using traditional silicon (Si) processing methods combined with this surface modification. The measured current-voltage characteristics were strongly dependent on both substrate type and molecular head group. The device behavior was analyzed using a qualitative model considering semiconductor depletion effects and molecular dipole moments and frontier orbital energies.