Applying bias voltage to improve rectification performance of molecular junction through side gate-group

Molecular diode is one of the most significant molecular devices for it being promised as electronic component in the molecular logic circuit. Controlling electronic transport to improve the rectification ratio of molecular diode is a crucial target for researchers. Here, based on the density functional theory and non-equilibrium Green's function method, the rectification performances of diblock co-oligomer molecules are investigated systematically. The numerical results show that, side gate-group can slightly enhance rectification ratios of diblock-molecule diodes, but it produces evident hindering effects on the electronic transports of the molecular junctions. Using electrode protrusion to contact with the side gate-group, the bias voltage is introduced to modulate the electronic transports of molecular junctions. By this strategy, the voltage at which the lowest unoccupied molecular orbital (LUMO) enters bias window is lowered evidently in the positive bias regime, which further significantly enhances the rectification ratios of the molecular diodes. The calculations additionally show that the LUMO is less delocalized under positive bias than it under negative bias, which is disadvantageous for enhancing the rectification performances of diblock co-oligomer molecular diode, thus very large rectification ratios are difficult to be achieved when one fabricates diblock co-oligomer molecular diodes in experimental fabrications.