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Phononic Amorphous Silicon: Theory, Material, and Devices

Published online by Cambridge University Press:  01 February 2011

Samrat Chawda
Affiliation:
schawda@ic.sunysb.edu, SUNY at Stony Brook, Materials Science and Engineering, Old Engineering Building,Department of Materials Science and Engineering, Stony Brook, NY, 11794, United States, 631-632-8513
Jose Mawyin
Affiliation:
jose.mawyin@gmail.com, SUNY at Stony Brook, Materials Science and Engineering, Stony Brook, NY, 11794, United States
Harv Mahan
Affiliation:
harv_mahan@nrel.gov, National Renewable Energy Laboratory, 1617 Cole Blvd.,, Golden, CO, 80401, United States
Charles Fortmann
Affiliation:
fortmann@ams.sunysb.edu, SUNY at Stony Brook, Applied Mathematics and Statistics, Stony Brook, NY, 11794, United States
Gary Halada
Affiliation:
ghalada@ms.cc.sunysb.edu, SUNY at Stony Brook, Materials Science and Engineering, Stony Brook, NY, 11794, United States
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Abstract

The field of phononic-engineered amorphous silicon is introduced. Specifically the construction of devices and waveguides for information conveyance and manipulation via phonons are considered. Typically the phononic properties of a given material are immutable and the phonons have such a limited diffusion length (nanometers) as to be unsuitable for engineering purposes. Crystalline silicon on the other hand has a reasonably large thermal conductivity and phonon diffusion length at sufficiently low temperatures. Phonon diffusion lengths can measure up to centimeters (e.g., crystalline SiO2) at temperature less than 10K but drop to sub microns at room temperature. Amorphous silicon, owing to the inherent scattering structures and owing to localization (of at least some phonon bands), has an anomalously large phonon lifetime [1]. This lifetime maybe indicative of a large phonon diffusion length and/or a fast phonon hop rate from one domain to the next and/or an indication that more than the typical three phonons (umklapp process) are involved in phonon scattering (e.g., see [1]&[2]). Techniques involving small-scaled devices and phonon bands to control umklapp phonon-phonon scattering are described. The potential to exploit inherent amorphous silicon structure as well as the engineering (post film deposition) of di-hydride distributions to induce phonon forbidden bands for significantly reduced multi-phonon scattering is explored. The indirect optical band gap of small domain (and possibly amorphous) silicon [3] provides the physical basis for the transduction of phonon and optical energies. Experimental methods for the post-deposition introduction of phonon scattering structure, the transduction of phononic information to optical information, and experimental approaches including the use of micro-Raman to probe phonon spectra and transport are described. The prospects of a fully integrated phononic, photonic, electronic amorphous silicon technology have been described.

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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