Tuning optical properties of 2D semiconductors by strain and electrostatic gating
Abstract/Contents
- Abstract
- Due to their two-dimensional (2D) nature, atomically thin transition metal dichalcogenides (TMDCs) exhibit properties that are greatly distinct from their bulk counterparts. At the single layer limit, the strong light-matter interaction and transition from indirect-gap to direct-gap enable new fundamental physics and optoelectronic applications. It is of great significance that the optical properties of atomically thin TMDCs could be controlled by external tuning knobs. In the dissertation, two external knobs are presented: strain and electrostatic gating. For strain tuning, we use bendable flexible substrates to apply uniaxial tensile strain to monolayer WSe2 samples and probe them with absorption and PL measurements. We show that tensile strain around 2.1% not only reduces the optical band gap by around 100 meV, but also greatly narrows the exciton linewidth. By modeling different components to excitonic linewidth, we attribute this reduction to the suppressed intervalley exciton-phonon scattering under tensile strain. This explanation is further consolidated by measurements on monolayer WS2 and bilayer WSe2. Another external tuning knob investigated is the presence of free charge carriers in the system, which could be injected into 2D materials by electrostatic gating. A high carrier concentration (~ 1013 cm-2) is realized through the electric-double-layer gating technique with ionic solid LaF3. Doping-dependent absorption measurements on monolayer WSe2 show that excitons are dissociated due to increased Coulomb screening at high free carrier concentrations. As a result, excitonic peaks are gradually replaced by a step-function like band-to-band transition feature in absorption spectra. Distinctive effects of screening and state filling due to free carriers are also observed through the different behaviors of A/B excitonic features. The works presented in this dissertation demonstrate that strain and electrostatic gating are two powerful knobs for both probing the fundamental physics in 2D semiconductors and realizing novel optoelectronic applications.
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource. |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2022; ©2022 |
| Publication date | 2022; 2022 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Deng, Minda |
|---|---|
| Degree supervisor | Heinz, Tony F |
| Thesis advisor | Heinz, Tony F |
| Thesis advisor | Lindenberg, Aaron Michael |
| Thesis advisor | Pop, Eric |
| Degree committee member | Lindenberg, Aaron Michael |
| Degree committee member | Pop, Eric |
| Associated with | Stanford University, Department of Applied Physics |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Minda Deng. |
|---|---|
| Note | Submitted to the Department of Applied Physics. |
| Thesis | Thesis Ph.D. Stanford University 2022. |
| Location | https://purl.stanford.edu/cm920hc9421 |
Access conditions
- Copyright
- © 2022 by Minda Deng
- License
- This work is licensed under a Creative Commons Attribution Non Commercial No Derivatives 3.0 Unported license (CC BY-NC-ND).
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