Role of Quantum Capacitance in a Carbon Nanotube Tunneling Device

Quantum capacitance is directly linked to the electronic density of states near the Fermi level in electronic devices and imposes constraints on the vertical scaling of field-effect transistors. In tunneling devices, the quantum capacitances associated with tunnel contacts strongly influence the tunneling spectrum. Here, we investigate a direct relationship between quantum capacitance and electronic density of states in a carbon nanotube device on the basis of van der Waals tunneling spectroscopy conducted on a carbon nanotube with a single indium contact. We observe multiple tunneling conductance peaks corresponding to the van Hove singularities of subbands in the nanotube. We demonstrate that quantum capacitances at these singularities of distinct subbands directly affect the coupling strength between the applied voltages and the effective potential within the nanotube, leading to observable changes in the slopes of the conductance peak lines in a plot of conductance as a function of the bias and gate voltages. Our theoretical model based on the quantum capacitance of a nanotube agrees with the experimental observations.