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published_or_final_version / abstract / toc / Physics / Master / Master of Philosophy

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The radiationless recombination of electron-hole pairs in semiconductors is inherently detrimental to the operation of optoelectronic technologies. Auger recombination, a prominent many-body scattering mechanism, facilitates efficient non-radiative recombination by transferring the released energy and momentum to a third carrier. In this thesis, ultrafast time-resolved two-photon photoemission is used to investigate the action of carriers subject to Auger scattering in two III-V semiconductor material systems, InGaN quantum well light-emitting diodes and bulk GaSb. In InGaN quantum wells, Auger recombination is believed to limit the radiative quantum efficiency at high carrier injection currents. Chapter 3 reports the direct observation of carrier loss from a single InGaN quantum well due to Auger recombination on the picosecond timescale. Selective excitations of the different valence sub-bands reveal that the Auger rate constant decreases by two orders of magnitude as the effective band mass decreases, confirming the critical role of momentum conservation in the Auger process. In Chapter 4, photoemission is used to directly detect Auger electrons as they scatter into high energy and momentum states of the GaSb conduction band. The Auger rate in GaSb is observed to be modulated by a coherent phonon mode at 2 THz, confirming phonon participation in momentum conservation. The commonly assumed Auger rate constant is also found to vary significantly, decreasing by four orders of magnitude as hot electrons cool by ~90 meV. These findings provide quantitative guidance in understanding Auger recombination and in designing a broader range of materials for efficient optoelectronics.

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The interactions of a model synthetic liquid fuel reactant (furan) with a model hydrodeoxygenation catalyst (clean and sulfided single crystal molybdenum) were investigated using the following UHV tools: Auger electron spectroscopy (AES), low energy electron diffraction (LEED), and temperature programed reaction spectroscopy (TPRS). In addition to furan, the reactions of hydrogen, carbon monoxide, ethylene, and propene on clean and sulfided Mo(110) were also examined. All adsorbates exposed to the extremely reactive clean or sulfided Mo(110) surface decomposed, yielding gaseous H��� and surface C. In addition, furan TPRS caused the production of gaseous CO. The presence of background hydrogen caused no major changes in the TPRS of furan or the other adsorbates. Sulfur pre-adsorption caused the chemical shifting of H��� TPRS peaks. Both sulfur and carbon pre-adsorption resulted in the Van der Waal's radius blocking of adsorption sites for all adsorbates studied. / Graduation date: 1997

Graduation date: 1997

Thesis (M. Sc.)--University of Adelaide, Dept. of Physics, 1985. / Includes bibliographical references (leaves 76-78).

Thesis--University of Oulu, 1987. / Includes bibliographical references (p. 43-46).

Thesis--University of Oulu, 1987. / Includes bibliographical references (p. 43-46).