Theory of Current Rectification, Switching, and a Role of Defects in Molecular Electronic Devices
Devices for nano- and molecular size electronics may allow for an efficient current rectification and switching. A few molecular scale devices are reviewed here on the basis of first-principles and model approaches. Current rectification by molecular quantum dots can produce the rectification ratio ≲100. Current switching due to conformational changes in the molecules is slow, on the order of a few kHz. Fast switching (~1 THz) may be achieved, at least in principle, in a molecular quantum dot with strong coupling with vibrational excitations. Defects in molecular films result in spurious peaks in conductance, apparent negative differential resistance, and may also lead to unusual temperature and bias dependence of current. The observed switching in most cases is extrinsic, caused by changes in molecule-electrode geometry, molecule reconfiguration, metallic filament formation through the film, etc.