{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/23916"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/23916","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"I. Excitonic phase diagram in Si: evidence for two condensed phases ; II. Motion of photoexcited carriers in GaAs/Alx̳Ga1̳-̳x̳As multiple quantum wells : anomalous confinement at high densities","abstract":"\"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. Excitonic Phase Diagram in Si: Evidence for Two Condensed Phases At low temperatures and sufficient densities, free excitons in Si and Ge undergo a simultaneous gas-liquid and insulator-metal transition into droplets of electron-hole liquid. Some previous theoretical and experimental studies have suggested that, under certain values of density and temperature, there may be separate metal-insulator and liquid-gas transitions. In the present paper, we examine the difficult trans-critical region for electron-hole liquid formation in unstressed Si using time-and space-resolved photoluminescence spectroscopy. Using the latest models for the luminescence of electron-hole plasma and small excitonic complexes (EC), we have succeeded in characterizing the complicated luminescence spectra both above and below the liquid-gas critical temperature (Tc(LG) ~ 24.5 K) with a relatively small number of free parameters. We find that the EHP density is remarkably independent of temperature and particle density, providing evidence for a second condensed phase of electron-hole III plasma. The new condensed liquid has a density of about one-tenth that of the ground-state electron-hole liquid (EHL), and is observed both above and below the EHL critical temperature. An excitonic phase diagram for silicon is described which includes two condensed plasmas. A triple point at 18.5 K is observed where the electron-hole liquid coexists with the lower density condensed plasma (CP) and excitonic gas. Above this temperature the CP is observed at all temperatures up to a second critical point at 45 5K. II. Motion of Photoexcited Carriers in GaAs/AlxGal-xAs Multiple Quantum Wells-Anomalous Confinement at High Densities We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 {lm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n =2 x 1011cm-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.\"","abstract_html":""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. Excitonic Phase Diagram in Si: Evidence for Two Condensed Phases At low temperatures and sufficient densities, free excitons in Si and Ge undergo a simultaneous gas-liquid and insulator-metal transition into droplets of electron-hole liquid. Some previous theoretical and experimental studies have suggested that, under certain values of density and temperature, there may be separate metal-insulator and liquid-gas transitions. In the present paper, we examine the difficult trans-critical region for electron-hole liquid formation in unstressed Si using time-and space-resolved photoluminescence spectroscopy. Using the latest models for the luminescence of electron-hole plasma and small excitonic complexes (EC), we have succeeded in characterizing the complicated luminescence spectra both above and below the liquid-gas critical temperature (Tc(LG) ~ 24.5 K) with a relatively small number of free parameters. We find that the EHP density is remarkably independent of temperature and particle density, providing evidence for a second condensed phase of electron-hole III plasma. The new condensed liquid has a density of about one-tenth that of the ground-state electron-hole liquid (EHL), and is observed both above and below the EHL critical temperature. An excitonic phase diagram for silicon is described which includes two condensed plasmas. A triple point at 18.5 K is observed where the electron-hole liquid coexists with the lower density condensed plasma (CP) and excitonic gas. Above this temperature the CP is observed at all temperatures up to a second critical point at 45 5K. II. Motion of Photoexcited Carriers in GaAs/AlxGal-xAs Multiple Quantum Wells-Anomalous Confinement at High Densities We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 {lm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n =2 x 1011cm-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."","abstract_has_math":false,"creators":["Smith, Leigh Morris"],"institution":null,"degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Physics","degree_department":null,"school":null,"contributors":["Wolfe, J.P."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2011,"date_issued":"2011-05-17T16:00:03Z","date_published":"2011-05-17T16:00:03Z","updated_at":"2026-07-22T22:25:22Z","subjects":["transport proteries","excitonic phase diagram","Si","Ge","condensed phases","motion of photoexcited carriers","GaAs","multiple quantum wells","anomalous confinement","high densities","thermodynamics"],"languages":["en"],"rights":["1988 Leigh Morris Smith"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["3502360"],"render_values":[{"text":"3502360","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/23916","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Wolfe, J.P."]},{"key":"dc:creator","label":"Author","values":["Smith, Leigh Morris"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2011-05-17T16:00:03Z","10000-01-01","1988"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation / Thesis","text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Physics"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["transport proteries","excitonic phase diagram","Si","Ge","condensed phases","motion of photoexcited carriers","GaAs","multiple quantum wells","anomalous confinement","high densities","thermodynamics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["en"]},{"key":"dc:rights","label":"Dc Rights","values":["1988 Leigh Morris Smith"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["3502360","http://hdl.handle.net/2142/23916"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["\"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. Excitonic Phase Diagram in Si: Evidence for Two Condensed Phases At low temperatures and sufficient densities, free excitons in Si and Ge undergo a simultaneous gas-liquid and insulator-metal transition into droplets of electron-hole liquid. Some previous theoretical and experimental studies have suggested that, under certain values of density and temperature, there may be separate metal-insulator and liquid-gas transitions. In the present paper, we examine the difficult trans-critical region for electron-hole liquid formation in unstressed Si using time-and space-resolved photoluminescence spectroscopy. Using the latest models for the luminescence of electron-hole plasma and small excitonic complexes (EC), we have succeeded in characterizing the complicated luminescence spectra both above and below the liquid-gas critical temperature (Tc(LG) ~ 24.5 K) with a relatively small number of free parameters. We find that the EHP density is remarkably independent of temperature and particle density, providing evidence for a second condensed phase of electron-hole III plasma. The new condensed liquid has a density of about one-tenth that of the ground-state electron-hole liquid (EHL), and is observed both above and below the EHL critical temperature. An excitonic phase diagram for silicon is described which includes two condensed plasmas. A triple point at 18.5 K is observed where the electron-hole liquid coexists with the lower density condensed plasma (CP) and excitonic gas. Above this temperature the CP is observed at all temperatures up to a second critical point at 45 5K. II. Motion of Photoexcited Carriers in GaAs/AlxGal-xAs Multiple Quantum Wells-Anomalous Confinement at High Densities We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 {lm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n =2 x 1011cm-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.\"","Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T16:00:03Z No. of bitstreams: 1 1988_smith.pdf: 5813548 bytes, checksum: 7c779f0e23a56fdbd321bb67b6485c3f (MD5)","Made available in DSpace on 2011-05-17T16:00:03Z (GMT). No. of bitstreams: 1 1988_smith.pdf: 5813548 bytes, checksum: 7c779f0e23a56fdbd321bb67b6485c3f (MD5) Previous issue date: 1988","Restriction data tranferred 2014-07-01T11:14:30-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T16:00:03Z Item is restricted indefinitely.","Thesis","U of I Only"]},{"key":"dc:title","label":"Title","values":["I. Excitonic phase diagram in Si: evidence for two condensed phases ; II. Motion of photoexcited carriers in GaAs/Alx̳Ga1̳-̳x̳As multiple quantum wells : anomalous confinement at high densities"]}]}],"canonical_facts":{"dc:contributor":["Wolfe, J.P."],"dc:creator":["Smith, Leigh Morris"],"dc:date":["2011-05-17T16:00:03Z","10000-01-01","1988"],"dc:description":["\"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. Excitonic Phase Diagram in Si: Evidence for Two Condensed Phases At low temperatures and sufficient densities, free excitons in Si and Ge undergo a simultaneous gas-liquid and insulator-metal transition into droplets of electron-hole liquid. Some previous theoretical and experimental studies have suggested that, under certain values of density and temperature, there may be separate metal-insulator and liquid-gas transitions. In the present paper, we examine the difficult trans-critical region for electron-hole liquid formation in unstressed Si using time-and space-resolved photoluminescence spectroscopy. Using the latest models for the luminescence of electron-hole plasma and small excitonic complexes (EC), we have succeeded in characterizing the complicated luminescence spectra both above and below the liquid-gas critical temperature (Tc(LG) ~ 24.5 K) with a relatively small number of free parameters. We find that the EHP density is remarkably independent of temperature and particle density, providing evidence for a second condensed phase of electron-hole III plasma. The new condensed liquid has a density of about one-tenth that of the ground-state electron-hole liquid (EHL), and is observed both above and below the EHL critical temperature. An excitonic phase diagram for silicon is described which includes two condensed plasmas. A triple point at 18.5 K is observed where the electron-hole liquid coexists with the lower density condensed plasma (CP) and excitonic gas. Above this temperature the CP is observed at all temperatures up to a second critical point at 45 5K. II. Motion of Photoexcited Carriers in GaAs/AlxGal-xAs Multiple Quantum Wells-Anomalous Confinement at High Densities We have measured the in-plane motion of photoexcited carriers in semiconductor quantum wells with 5 {lm spatial and 10 ps temporal resolution and have discovered several surprising results. The effective diffusivity of the carriers at densities below n =2 x 1011cm-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.\"","Submitted by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T16:00:03Z No. of bitstreams: 1 1988_smith.pdf: 5813548 bytes, checksum: 7c779f0e23a56fdbd321bb67b6485c3f (MD5)","Made available in DSpace on 2011-05-17T16:00:03Z (GMT). No. of bitstreams: 1 1988_smith.pdf: 5813548 bytes, checksum: 7c779f0e23a56fdbd321bb67b6485c3f (MD5) Previous issue date: 1988","Restriction data tranferred 2014-07-01T11:14:30-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: Thesis","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Carolyn Mead (cmead2@illinois.edu) on 2011-05-17T16:00:03Z Item is restricted indefinitely.","Thesis","U of I Only"],"dc:identifier":["3502360","http://hdl.handle.net/2142/23916"],"dc:language":["en"],"dc:rights":["1988 Leigh Morris Smith"],"dc:subject":["transport proteries","excitonic phase diagram","Si","Ge","condensed phases","motion of photoexcited carriers","GaAs","multiple quantum wells","anomalous confinement","high densities","thermodynamics"],"dc:title":["I. Excitonic phase diagram in Si: evidence for two condensed phases ; II. Motion of photoexcited carriers in GaAs/Alx̳Ga1̳-̳x̳As multiple quantum wells : anomalous confinement at high densities"],"dc:type":["Dissertation / Thesis","text"],"thesis:degree_discipline":["Physics"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."]},"updated_at":"2026-07-22T22:25:22Z"}