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|Title:||Interaction of Nonequilibrium Phonons With Electron-Hole Plasmas in Germanium (Liquid, Excitons, Phase Diagram)|
|Author(s):||Kirch, Steven James|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|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, superconducting 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 Fermi energy of the EHL along certain directions and the corresponding restriction on the allowed scattering (the 2k(,F)-cutoff) is observed.
In the second experiment, presented in Chapter 3, the non-equilibrium phonons are generated by laser excitation of a metal film. An unusual sample geometry 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 recombination luminescence is examined. A "phonon wind" force is observed to dominate 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.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1985.
|Date Available in IDEALS:||2015-05-13|