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oai:www.ideals.illinois.edu:2142/77421 2023-07-11 col_2142_5131 col_2142_8859 com_2142_5130 com_2142_8858 com_2142_234

Smith, Leigh Morris 2015-05-13T15:42:02Z 2015-05-13T15:42:02Z 10000-01-01 1988 1988 This thesis describes work on the thermodynamics and transport properties of photoexcited carriers in bulk and two-dimensional semiconductors. Two major topics are addressed. I. Photoluminescence experiments of excitons in unstressed silicon are presented which indicate the existence of a new non-degenerate condensed phase of plasma. This new liquid has a density one-tenth that of the ground state electron-hole liquid and is observed both above and below the liquid-gas critical point ($\approx$24.5K). A new phase diagram of excitons in silicon is presented which includes these two condensed plasmas. Consistent with the Gibbs phase rule, a triple point at 18.5 K is inferred from the luminescence data as the only temperature where the exciton gas, condensed plasma (CP) and electron-hole liquid (EHL) coexist. The low density condensed plasma persists up to a second critical point at 45 $\pm$ 5K, above which the photoexcited carriers are observed to continuously decay into a partially ionized excitonic gas. II. We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 $\mu$m spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n = 2 $\times$ 10$\sp $cm$\sp{-2}$ is found to depend upon excitation level, possibly indicating defect-limited diffusion or phonon-wind effects. Above this density the spatial profiles exhibit two distinct components with widely differing diffusivities. This remarkable behavior may be understood with consideration of the interactions of non-equilibrium phonons with the photoexcited carriers. We postulate that the slowly diffusing component represents carriers which are "thermally confined" to a phonon hot spot, while the rapidly moving component is driven by the flux of non-equilibrium phonons away from the excitation region. Made available in DSpace on 2015-05-13T15:42:02Z (GMT). No. of bitstreams: 2 license.txt: 4848 bytes, checksum: 96035ab3f5e1c23cc7138a224ce498bd (MD5) 8823253.PDF: 5404952 bytes, checksum: 658be56c13c21a08bd9d4c4e2d0584ef (MD5) Previous issue date: 1988 Embargo set by: Seth Robbins for item 78632 Lift date: Forever Reason: Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs Restricted to the U of I community idenfinitely during batch ingest of legacy ETDs U of I Only 166 p. Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988. http://hdl.handle.net/2142/77421 (UMI)AAI8823253 eng Physics, Condensed Matter I. Excitonic Phase Diagram in Silicon: Evidence for Two Condensed Phases. II. Motion of Photoexcited Carriers in Gallium-Arsenide/aluminum(x)gallium(1-X)arsenide Multiple Quantum Wells--Anomalous Confinement at High Densities text Physics Physics University of Illinois at Urbana-Champaign Dissertation Ph.D.