Smith, Mark John (1989) Low temperature phonon-drag thermoelectric power calculations in GaAs/GaAlAs heterojunctions and Si MOSFETs. PhD thesis, University of Warwick.

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Abstract

The effect on the electron transport of the confinement of the electrons to a narrow
channel in GaAs/GaAlAs heterojunctions and Si MOSFETs is reflected in quantities like
the thermopower (S) which is sensitive to the transport of both heat and charge. The
calculations described here confirm that in these systems S is dominated by phonondrag
(Sg) at temperatures (T) around 1-10K and reveals more sensitivity than previously
imagined.
Simple models and the Boltzmann transport formalism have been investigated. The
formalism enhances the predictions of the simple models and reproduces the simple S.
formulae in appropriate limits. Amplification of S9 in quasi-2D arises from the loss of the
momentum conservation constraint across the channel at small widths b.
Earlier calculations were numerically inaccurate and greatly overestimate -S9 by ignoring
screening. An effective multi-subband screening dielectric function is defined which
reduces to the single subband approximation at small b and low electron density (n). Nondegeneracy
has also been included. It is an important consideration despite the low temperatures
of most of the data. The treatment of electron confinement has been improved
and the temperature dependence of the polarizability investigated. It is unimportant in
the current experimental systems but significant at lower n and higher T.
The piezoelectric scattering mechanism has been introduced and dominates S. in the
heterojunction for T <1K. A dominant 2D wavevector component has been defined for
the phonon population at given T which is very helpful in understanding S9. A correction
for the energy dependence of the electron relaxation-time is necessary and demonstrates
the dependence of S. upon the dominant electron scattering mechanism.
The calculations of S. in the quantum-limit and boundary scattering regime now explain
the measured S in heterojunctions and peaks in -Sg/T3 in the MOSFET up to an
accuracy better than 10% without adjustable parameters.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QC Physics
Library of Congress Subject Headings (LCSH):	Phonons, Conduction electrons, Thermoelectricity, Electron gas, Heterojunctions
Official Date:	September 1989
Dates:	Date Event September 1989 Submitted
Institution:	University of Warwick
Theses Department:	Department of Physics
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Butcher, Paul N.
Extent:	134 leaves
Language:	eng
URI:	http://wrap.warwick.ac.uk/id/eprint/4163

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