Date of Graduation

5-2015

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Electrical Engineering

Advisor

Samir M. El-Ghazaly

Committee Member

Hameed A. Naseem

Second Committee Member

Douglas Spearot

Keywords

Pure sciences; Applied sciences; Carbon nanotube; Contact resistance; Tera hertz

Abstract

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's 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.