Engineering Epitaxial Graphene-based 2D Heterojunctions for Electronic and Optoelectronic Applications
Open Access
- Author:
- Subramanian, Shruti
- Graduate Program:
- Materials Science and Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- May 11, 2020
- Committee Members:
- Joshua Alexander Robinson, Dissertation Advisor/Co-Advisor
Joshua Alexander Robinson, Committee Chair/Co-Chair
Roman Engel-Herbert, Committee Member
John B Asbury, Committee Member
Saptarshi Das, Outside Member
Susan K. Fullerton-Shirey, Special Member
Ursula Wurstbauer, Special Member
John C Mauro, Program Head/Chair - Keywords:
- 2D materials
Heterostructures
Lateral Heterostructures
Epitaxial Graphene
MoS2
Contacts
Optoelectronics
Electronics
Intercalation
Photocurrent
nano-ARPES
Tunable - Abstract:
- Two-dimensional (2D) materials have exhibited great promise for several electronic and optoelectronic applications. Depending on the complexity of the technology, they lie on various sections of the Gartner Hype cycle. With the famous pencil and scotch tape success story, graphene was the first of this family of van der Waals materials to open up a forte of either 2D-based or 2D-enabled technologies. The combination of different 2D materials allows the construction of vertical and lateral 2D heterostructures. The work presented in this dissertation focuses on epitaxial graphene-based heterostructures for electronic and optoelectronic applications. Chapter 1 presents the motivation of the dissertation study from the key technology drivers identified from the United States Grand Challenges. Before delving into the discussion of the results presented in this dissertation, Chapter 2 lays down the necessary basics of 2D materials and devices. It ranges from explaining graphene, its physics, synthesis and intercalation to transition metal dichalcogenides (TMDs), their physics and synthesis. An introduction to the electronic devices used in this dissertation follows next along with the basics of device fabrication and ends with the fundamentals of ellipsometry. Chapter 3 gets more specific and outlines all the experimental procedures used during the course of this dissertation including the microscopy and spectroscopy techniques used to understand the complex heterostructure systems synthesized. 2D materials are finding a niche spot in high-performance and energy-efficient computing, but fundamental problems arise due to contacts, which are connections between the 2D material and the 3D world. Chapter 4 of this dissertation focuses on developing a technique to synthesize seed-free selected-area lateral heterostructures with an as-grown graphene contact to TMDs like MoS2. 2D-only or 2D-enabled architectures are finding a place in the development of photovoltaics for economical solar energy. Chapter 5 of this dissertation focuses on understanding the photocurrent generation and subsequent dissociation of charge carriers at heterostructure interfaces in large-area scalable graphene/MoS2 architectures. The in-depth understanding of optoelectronic properties of heterostructure interfaces allows for expansion to application-specific engineering of heterostructure interfaces with improved contacts and extraction of photogenerated current. Atomically thin electronic materials are finding niche applications in electronics, sensors, and transmitters, and coatings among several other technologies, furthering the next technology driver - the Internet of Things. Chapter 6 of this dissertation focuses on as-grown graphene contacts to MoS2 and utilizes a unique property of enabling electrostatic modulation of the intrinsic doping of epitaxially grown graphene on SiC from n- to p-type, providing an additional knob for tuning 2D heterojunctions. Intercalation of metals between the graphene and SiC is yet another route for tuning and an excellent platform for biosensing applications; it further allows for the exploration of novel 2D metals. Chapter 7 of this dissertation is focused on understanding the optical properties of these novel 2D metals to integrate them into functional heterostructures. An outlook is presented in Chapter 8 along with future directions that can be explored within the realm of the work presented in this dissertation. The future directions are presented in the same format as the motivation, tying the two ends of this dissertation together. The works of this dissertation were primarily funded by National Science Foundation’s CAREER (Award: 1453924). The findings and conclusions of this dissertation work does not necessarily reflect the view of the National Science Foundation.