The Difficulty of Gate Control in Molecular Transistors

TL;DR

This paper investigates how electrostatic gating influences molecular transistors using DFT and NEGF, revealing challenges in gate control during the turn-on process due to minimal energy level shifts near the Fermi energy.

Contribution

It demonstrates the limitations of gate control in molecular transistors, especially when molecular energy levels approach the Fermi energy, highlighting a fundamental challenge for device implementation.

Findings

Energy levels shift linearly when away from Fermi energy.

Near the Fermi energy, shifts become negligible during turn-on.

Gate control of conductance is limited in the 'ON' state.

Abstract

The electrostatic gating effects on molecular transistors are investigated using the density functional theory (DFT) combined with the nonequilibrium Green's function (NEGF) method. When molecular energy levels are away from the Fermi energy they can be linearly shifted by the gate voltage, which is consistent with recent experimental observations [Nature 462, 1039 (2009)]. However, when they move near to the Fermi energy (turn-on process), the shifts become extremely small and almost independent of the gate voltage. The fact that the conductance may be beyond the gate control in the "ON" state will challenge the implementation of molecular transistors.