Gate-tunable step-like current through a single-molecule junction

Using the kinetic approach, analytical expressions are obtained for the sequential and direct tunneling components of the current in a molecular junction, where the molecule acts as a mediator for interelectrode electron transfer. Within the framework of the modified HOMO-LUMO model, it is shown that the current components are not independent even with weak interaction of the molecule with the electrodes but are interrelated kinetically through processes that lead to the occupation of the electronic states of a charged and neutral molecule. As an application of the theory, the critical voltages determining the ranges of resonant steplike electron transfer through a junction with a planar ZnPc molecule are estimated. The values of the gate voltages at which the junction is capable of performing the functions of photoemitter are presented.