Perello, David
(2013)
Contact Metal-Dependent Electrical Transport in Carbon Nanotubes and Fabrication of Graphene Nanoribbons.
Doctoral Dissertation, University of Pittsburgh.
(Unpublished)
Abstract
In this thesis, we fabricate and characterize carbon nanotube (CNT) and graphene-based field effect transistor devices. The CNT-based work centers on the physics of metal contacts to CNT, particularly relating the work function of contact metals to carrier transport across the junction. The graphene work is motivated by the desire to utilize the high carrier mobility of graphene in field effect transistors.
We introduce a surface-inversion channel (SIC) model based on low temperature and electrical measurements of a distinct single-walled semiconducting CNT contacted by Hf, Cr, Ti and Pd electrodes. Anomalous barrier heights and metal-contact dependent band-to-band tunneling phenomena are utilized to show that dependent upon contact work function and gate field, transport occurs either directly between the metal and CNT channel or indirectly via injection of carriers from the metal-covered CNT region to the CNT channel. The model is consistent with previously contradictory experimental results, and the methodology is simple enough to apply in other contact-dominant systems.
We further develop a model explain Isd-Vsd tendencies in CNT FETs. Using experimental and analytical analysis, we demonstrate a relationship between the contact metal work function and electrical transport properties saturation current (Isat) and differential conductance in ambient exposed CNT. A single chemical vapor deposition (CVD)-grown 6 millimeter long semiconducting single-walled CNT is electrically contacted with a statistically significant number of Hf, Cr, Ti, Pd, and Ti, Au electrodes, respectively. The observed exponentially increasing relationship of Isat and with metal-contact work function that is explained by a theoretical model derived from thermionic field emission.
Next, a performance analysis on CNT Schottky diodes using source-drain current anisotropy is explored. An analytical model is derived based on thermionic field emission and used to correlate experimental data from Pd-Hf, Ti-Hf, Cr-Hf, Ti-Cr, and Pd-Au mixed metal devices fabricated on one single 6 mm-long CNT. Results suggest that the difference in work functions of the two contact-metals, and not a dominant Schottky contact, determines diode performance. Results are further applied and demonstrated in a reversible polarity diode.
Lastly, we investigate the effect of UV irradiation of graphene, CNT, and graphene/CNT hybrids in an oxygen environment. Samples were irradiated by 254/185 nm UV light in an oxygen environment for up to two hours. Results suggest a unique method to generate graphene nanoribbons using aligned carbon nanotubes (CNT) as a graphene etch mask. Ambient and cryogenic Gsd-Vg measurements of resulting ultra-thin graphene nanoribbons show p-type character and field effect GOn/GOff > 10^4.
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Details
| Item Type: |
University of Pittsburgh ETD
|
| Status: |
Unpublished |
| Creators/Authors: |
|
| ETD Committee: |
|
| Date: |
28 June 2013 |
| Date Type: |
Publication |
| Defense Date: |
29 March 2013 |
| Approval Date: |
28 June 2013 |
| Submission Date: |
2 April 2013 |
| Access Restriction: |
No restriction; Release the ETD for access worldwide immediately. |
| Number of Pages: |
130 |
| Institution: |
University of Pittsburgh |
| Schools and Programs: |
Swanson School of Engineering > Electrical Engineering |
| Degree: |
PhD - Doctor of Philosophy |
| Thesis Type: |
Doctoral Dissertation |
| Refereed: |
Yes |
| Uncontrolled Keywords: |
Carbon Nanotube, Schottky Barrier, Metal-Semiconductor Contact, Graphene, Electrical Transport, Growth, Graphene Growth, Graphene Nanoribbon |
| Date Deposited: |
28 Jun 2013 19:51 |
| Last Modified: |
15 Nov 2016 14:11 |
| URI: |
http://d-scholarship.pitt.edu/id/eprint/18068 |
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