Optical Science and Engineering ETDs

Publication Date



Despite all of the promising properties that graphene has, there are some challenges facing graphene technology. Graphene lacks a bandgap, which limits its application in digital electronics and optoelectronics. Since the year 2010, extensive e\ufb00orts have been made to create semiconducting graphene without disrupting its exceptional transport properties. One method is to obtain bandgap through quantum con\ufb01nement in graphene nanoribbons (GNRs) and graphene nanomesh (GNM) with a critical dimension lower than 10 nm. As a part of this dissertation, interferometric lithography combined with oxygen O2 plasma treatment is demonstrated to be an e\ufb03cient method to fabricate GNMs with sub-10 nm neck widths and uniformity over a 1 cm2 area. Atomic force microscopy and Raman spectroscopy are used to characterize the neck width of GNMs. FETs with GNM channel widths of 2 mm have been fabricated to demonstrate its application in electronic devices. Transfer characteristics of the GNM-device are also studied at room and cryogenic temperatures. Another area that is explored in this dissertation is the lateral charge transport in graphene (Gr)/germanium (Ge) heterojunctions. Gr/Ge has recently shown a tremendous potential for application in graphene synthesis, analog electronics and infrared (IR) detecting [6]. Despite the increasing body of literature on graphene on Ge, the physical and electronic structure of the Gr/Ge interface is still poorly characterized, and lateral transport in this material combination is not well understood. To date, Cavallo et al. [5] have provided the only reported values of mobility and carrier concentration of Gr supported by a Ge substrate. In this work we investigate the physical and electronic structure of the Gr/Ge in terface, and how it a\ufb00ects lateral transport in graphene transferred to a Ge nanomembrane (NM). Our study includes fabrication and characterization of GFET on Ge NMs, transfer length model (TLM), and structural analysis by X-ray photoelectron spectroscopy, atomic force microscopy, transmission electron microscopy and electron energy-loss spectroscopy. We trace the position of Dirac point voltage to investigate the potential charge transfer. In addition TLM measurement was performed to extract the sheet resistance of graphene on di\ufb00erent germanium substrates namely Gr/germanium on insulator (GOI) and Gr/transferred Ge/SiO2/p+Si and then compared with the sheet resistance of Gr/SiO2/p+Si. The electrical transport parameters obtained from the experimental techniques and theoretical modeling were used to extract the key transport parameters of the Gr/Ge heterojunction.

Degree Name

Optical Science and Engineering

Level of Degree


Department Name

Optical Science and Engineering

First Advisor

Krishna, Sanjay

First Committee Member (Chair)

Brueck, Steven

Second Committee Member

Cavallo, Francesca

Third Committee Member

Habteyes, Terefe

Document Type




Available for download on Wednesday, May 16, 2018