Schottky-barrier double-walled carbon-nanotube field-effect transistors

We investigate electronic transport properties of Schottky-barrier field-effect transistors (FETs) based on double-walled carbon nanotubes (DWCNTs) with a semiconducting outer shell and a metallic inner one. This kind of DWCNT-FETs shows asymmetries of the $I\text{−}V$ characteristics and threshold voltages due to the electron-hole asymmetry of the Schottky barrier. The presence of the metallic inner shell induces a large effective band gap, which is one order of magnitude larger than that due to the semiconducting shell alone of a single-walled carbon-nanotube FET.

Figure 1

(Color online) (a) Schematic experimental setup of a DWCNT-FET. A DWCNT is connected with source and drain contacts. A gate is insulated from the DWCNT by a dielectric material with dielectric constant $ϵ$. (b) A theoretical model describing the setup in (a). The FET consists of a DWCNT with a semiconducting outer shell and a metallic inner one. Only the outer shell is end bonded to the source and drain contacts and the inner one is insulated from both leads. A cylindrical gate is deposited on the dielectric material surrounding the DWCNT.

Figure 2

(Color online) (a) Calculated zero temperature $I\text{−}{V}_{sd}$ characteristics of a DWCNT-FET with different gate voltages: $V_g=0\mathrm{V}$ (dashed line), $V_g=0.4\mathrm{V}$ (solid line), and $V_g=0.8\mathrm{V}$ (dot-dashed line). The DWCNT has an outer shell with radius $R_o=1.34\mathrm{nm}$ and an inner one with radius $R_i=1\mathrm{nm}$. Its length is $L=200\mathrm{nm}$. The inner shell potential is $V_i=0\mathrm{V}$. [(b) and (c)] Band diagrams of the conduction and valence band edges of the semiconducting outer shell in two configurations indicated by two crosses in (a). The dot-dashed line denotes the chemical potential in the outer shell. The two short thin solid lines show the chemical potentials in source (left) and drain (right) leads, respectively.

Figure 3

(Color online) Transfer characteristics of a DWCNT-FET with a constant bias voltage $V_{sd}=0.05\mathrm{V}$ but different inner shell potentials: $V_i=0\mathrm{V}$ (solid line) and $V_i=-0.04\mathrm{V}$ (dashed line). The remaining parameters are the same as those in Fig. 2. Inset: Transfer characteristics of a SWCNT-FET with radius $R=1.34\mathrm{nm}$, which is the same as the outer shell radius of the DWCNT.