Interaction of non-equilibrium phonons with electron-hole plasmas in germanium
Kirch, Steven James
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https://hdl.handle.net/2142/25290
Description
Title
Interaction of non-equilibrium phonons with electron-hole plasmas in germanium
Author(s)
Kirch, Steven James
Issue Date
1985
Director of Research (if dissertation) or Advisor (if thesis)
Wolfe, J.P.
Department of Study
Physics
Discipline
Physics
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
non-equilibrium phonons
electron-hole plasmas
germanium
electron-hole liquid (EHL)
electron-hole plasma (EHP)
Language
en
Abstract
"This thesis presents results of experiments on the interaction of phonons and photo-excited electron-hole plasmas in Ge at low
temperature. The first two studies involve the low temperature fluid phase known as the electron-hole liquid (EHL). The third study involves a wider range of temperatures and includes the higher temperature electron-hole plasma (EHP).
In the first experiment, presented in Chapter 2, superconduct1ng tunnel junctions are used to produce quasi-monochromatic phonons, which
propagate through the EHL. The magnitude of the absorption of these non-equilibrium phonons gives a direct measure of the coupling
constant, the deformation potential. A full Boltzmann equation solution including carrier-carrier scattering is necessary to explain the results. Uniaxial stress is used to tune the Fenni energy of the EHL along certain directions and the corresponding restriction on the
allowed scattering (the 2kf-cutoff) is observed..
In the second exper1ment, presented in Chapter 3, the non-equilibrium phonons are generated by laser excitation of a metal film. An unusual sample geanetry allows examination of the EHL-phonon interaction near the EHL excitation surface. This coupling is examined
for both cw and pulsed EHL excitation. The long tail associated with the signal from a high-energy phonon excitation pulse is seen to be due to bulk scattering.
In the third experiment, presented in Chapter 4, the phonons are byproducts of the photo-excited carrier thermalization. The spatial, spectral and. temporal dependence of the recanb1nation luminescence is examined. A ""phonon wind"" force is observed to daninate the transport properties of the EHL and. the EHP. These carriers are never observed to move faster than the phonon velocity even during the laser pulse. In Chapter 5 it is shown that these spectra can be fit with lineshapes associated with a Fermi fluid, free excitons and. excitonic molecules. Evidence is found that the EHP undergoes an additional first order phase transition to free excitons above the established liquid-gas critical temperature."
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