MIT Libraries logoDSpace@MIT

MIT
View Item 
  • DSpace@MIT Home
  • MIT Libraries
  • MIT Theses
  • Doctoral Theses
  • View Item
  • DSpace@MIT Home
  • MIT Libraries
  • MIT Theses
  • Doctoral Theses
  • View Item
JavaScript is disabled for your browser. Some features of this site may not work without it.

Phonon and electron transport through interfaces and disordered structures

Author(s)
Song, Qichen
Thumbnail
DownloadThesis PDF (11.91Mb)
Advisor
Chen, Gang
Henry, Asegun
Terms of use
In Copyright - Educational Use Permitted Copyright MIT http://rightsstatements.org/page/InC-EDU/1.0/
Metadata
Show full item record
Abstract
Understanding phonon and electron transport is of great significance for designing efficient solid-state devices such as transistors, laser diodes and thermoelectric energy converters. The structural randomness is inevitable in solid-state devices, and it is often regarded as the undesirable scattering source for phonons and electrons. This thesis studies manipulating phonon and electron flow using structural randomness via mode-resolved Green’s function calculations and pump-probe optical characterizations. Interface roughness is a common type of randomness in heterostructures, which strongly affects electron and phonon transport across interfaces. We find that atomically rough interfaces can scatter short-wavelength electrons and assist the transmission between mismatched valleys. The contact resistance is reduced by over an order of magnitude. Our study provides new insights on the conventional wisdom to improve the interfacial transport using graded interfaces. We also use the atomistic Green’s function to simulate phonon transport across rough interfaces to show that the basic assumption that phonons lose memories in the often-used diffuse phonon scattering model is questionable. The coherent backscattering of waves in disordered structures can lead to Anderson localization, where the waves are spatially localized and cannot propagate. Anderson localization has been observed in electronic, photonic and acoustic systems. However, observing its impact on heat conduction is challenging due to the broadband nature and three-dimensional transport of phonons. We use the aperiodicity as a type of randomness to enhance phonon Anderson localization. Our calculation predicts that aperiodic Si/Si0.2Ge0.8 superlattice can induce coherent backscattering for low-frequency phonons and limit the contribution to transport of high-frequency phonons. The interferences among scattered low-frequency phonons lead to a peak in the thermal conductivity versus length curve, a characteristic feature of phonon Anderson localization. Using frequency-domain thermoreflectance, we validate our theoretical predictions and find that the phonon Anderson localization exists up to 200 K. Our findings provide an efficient approach to localize phonons at moderate temperatures using randomness.
Date issued
2022-02
URI
https://hdl.handle.net/1721.1/143341
Department
Massachusetts Institute of Technology. Department of Mechanical Engineering
Publisher
Massachusetts Institute of Technology

Collections
  • Doctoral Theses

Browse

All of DSpaceCommunities & CollectionsBy Issue DateAuthorsTitlesSubjectsThis CollectionBy Issue DateAuthorsTitlesSubjects

My Account

Login

Statistics

OA StatisticsStatistics by CountryStatistics by Department
MIT Libraries
PrivacyPermissionsAccessibilityContact us
MIT
Content created by the MIT Libraries, CC BY-NC unless otherwise noted. Notify us about copyright concerns.