Two dimensional (2D) materials are poised to revolutionize the
future of optics and electronics. The past decade saw intense research
centered around graphene. More recently, the tide has shifted to a bigger
class of two-dimensional materials including graphene but more
expansive in their capabilities. The so called ‘2D material zoo’ includes
metals, semi-metals, semiconductors, superconductors and insulators.
The possibility of mixing and matching 2D materials to fabricate
heterostructures with desirable properties is very exciting.
To make devices with superior electronic, optical and thermal
properties, we need to understand how the electrons, phonons and other
quasi particles interact with each other and exchange energy in the
femtosecond and nanosecond timescales. To measure the timescales of
energy distribution and dissipation, I used ultrafast pump-probe
spectroscopy to perform time-domain measurements of optical
absorption. This approach allows us to understand the impact of manybody
interactions on the bandstructure and carrier dynamics of 2D
materials.
After a brief introduction to femtosecond laser spectroscopy, I will
explore the transient absorption dynamics of three classes of 2D
materials: intrinsic graphene, graphene-hBN heterostructures and
Transition Metal Dichalcogenides (TMDs). We will see that using pumpprobe
measurements around the high energy M-point of intrinsicgraphene, we can extract the value of the acoustic deformation potential
which is vital in characterizing the electron-acoustic phonon
interactions. In the next part of the thesis, I will delineate the role of the
substrate in the cooling dynamics in graphene devices. We will see that
excited carriers in graphene on hBN substrates cool much faster that on
SiO2 substrates due to faster decay of the optical phonons in graphenehBN
heterostructures. These results show that graphene-hBN
heterostructures can solve the hot phonon bottleneck that plagues
graphene devices at high power densities. In the last part, I will
demonstrate the role of phonon induced bandgap renormalization in the
carrier dynamics of TMD materials and measure the timescale of
phonon decay through the generation of low-energy phonons and
transfer to the substrate. This study will help us understand carrier
recombination in TMD devices under high-bias conditions which show
great potential in opto-electronic applications such as photovoltaics,
LEDs etc.
| Identifer | oai:union.ndltd.org:arizona.edu/oai:arizona.openrepository.com:10150/626303 |
| Date | January 2017 |
| Creators | Golla, Dheeraj, Golla, Dheeraj |
| Contributors | Sandhu, Arvinder S., Sandhu, Arvinder S., LeRoy, Brian J., Schaibley, John R., Wang, Weigang |
| Publisher | The University of Arizona. |
| Source Sets | University of Arizona |
| Language | en_US |
| Detected Language | English |
| Type | text, Electronic Dissertation |
| Rights | Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. |
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