Single-Walled Carbon Nanotube Arrays for High Frequency Applications

This dissertation presents a thorough analysis of semiconducting Single-Walled Carbon Nanotube-based devices, followed by a test structure fabrication and measurements. The analysis starts by developing an individual nanotube model, which is then generalized for many nanotubes and adding the parasitic elements. The parasitic elements appear when forming the device electrodes degrade the overall performance. The continuum model of an individual nanotube is developed. A unique potential function is presented to effectively describe the electron distribution in the carbon nanotube subsequently facilitating solving Schrödinger\u27s equation to obtain the energy levels, and to generalize the model for many nanotubes. It is shown that the overall energy band gap is inversely proportional to the number of nanotubes due to the coupling between the nanotubes. The coupling is then enhanced by applying an external transverse electric field, which controls the energy band gap. The electric field is represented as a function of the number of nanotubes per device showing that the higher the number of nanotubes, the lower the value of the electric field needed to alter the energy band gap. An electromagnetic model is developed for the contact where a detailed parametric study of the length, thickness, and conductivity of the contact area is presented. The overlap length between the nanotube and the metal of the contact appears to be the dominating factor.There is a clear inverse proportionality between overlap length and contact resistance to reach a minimum value after an effective overlap length. An equation is developed to describe the conductance as a function of the number of nanotubes per device. A four-electrode test structure is fabricated using both photolithography and electron-beam-lithography. The carbon nanotubes are deposited using the dielectrophoresis method for many devices simultaneously to provide a sheet resistance as low as 10 K/. The I-V characteristics are measured with and without change in the transverse electric field. It shows a change in the current reflecting the changes in the energy band gap discussed earlier. There are many applications for the results presented in this dissertation such as optimizing devices operating in the THz frequency range

Energy Band Gap Study of Semiconducting Single Walled Carbon Nanotube Bundle

The electronic properties of multiple semiconducting single walled carbon nanotubes (s-SWCNTs) considering various distribution inside a bundle are studied. The model derived from the proposed analytical potential function of the electron density for an individual s-SWCNT is general and can be easily applied to multiple nanotubes. This work demonstrates that regardless the number of carbon nanotubes, the strong coupling occurring between the closest neighbours reduces the energy band gap of the bundle by 10%. As expected, the coupling is strongly dependent on the distance separating the s-SWCNTs. In addition, based on the developed model, it is proposed to enhance this coupling effect by applying an electric field across the bundle to significantly reduce the energy band gap of the bundle by 20%