Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2002. / Includes bibliographical references (p. 180-188). / This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections. / Monolithic optoelectronic integration on silicon-based integrated circuits has to date been limited to date by the large material differences between silicon (Si) and the direct-bandgap GaAs compounds from which optoelectronic components are fabricated. Graded Ge/GeSi buffer layers grown on standard Si substrates have been shown to produce near-lattice matched virtual substrates for GaAs integration on Si. This study investigated the crystal growth conditions and device fabrication techniques necessary for successful GaAs-based laser integration on Ge/GeSi buffer layers on Si substrates. The nucleation conditions for GaAs on Ge/GeSi/Si substrates have been comprehensively examined. High-temperature ( 2 700⁰ C) initiation with properly chosen V/III gas flow ratio yields high-quality, stacking fault-free GaAs films on Ge/GeSi/Si substrates, but also encourages the vapor-phase transport of Ge from the substrate into the active regions of integrated GaAs devices. A new two-step GaAs nucleation process was developed that enabled the first demonstration of high-quality Ge-free GaAs light-emitting diodes on Ge/GeSi/Si substrates. The large thermal expansion mismatch between Si, Ge, and GaAs introduces additional strain to integrated device layers on Ge/GeSi/Si substrates grown at high temperatures. This study conclusively demonstrated the link between thermal mismatch strain and increased misfit dislocation formation in InxGa(lx)As/GaAs quantum well structures integrated on Ge/GeSi/Si substrates. / (cont.) The thermal mismatch strain was successfully countered by the introduction of compressive InGaAs graded buffer layers above the Ge/GeSi/Si substrate surface, and strain-free GaAs layers at growth temperatures suitable for laser integration have been demonstrated. The integration of edge-emitting heterostructure lasers on Ge/GeSi/Si substrates introduces additional waveguide design issues addressed by this study. Low-index Alo.6Gao.4As cladding layers, along with a graded-index separate confinement heterostructure, were introduced to reduce photon losses. Interfacial roughness transmitted from the Ge/GeSi/Si substrate was reduced with a pre-growth chemical-mechanical polishing step, and smooth mirror facets on integrated devices were fabricated by cleaving thinned lasers parallel to the substrate offcut direction. Continuously operating edge-emitting GaAs/AlGaAs quantum well lasers on Ge/GeSi/Si substrates were demonstrated at room temperature with an operating wavelength of 858 nm. Series resistance heating in early devices was reduced by the introduction of a top-contact geometry and optimized cladding layer structure, and improved laser diodes had a differential quantum efficiency of 40%, a threshold current density of 269 A/cm2, and a characteristic temperature of 129 K. Identical devices fabricated on GaAs substrates had similar performance characteristics. Lasers on Ge/GeSi/Si substrates fell below threshold after 4 hours of continuous operation-a dramatic improvement over early measured lifetimes of less than 20 minutes ... / by Michael Edward Groenert. / Ph.D.
| Identifer | oai:union.ndltd.org:MIT/oai:dspace.mit.edu:1721.1/16876 |
| Date | January 2002 |
| Creators | Groenert, Michael |
| Contributors | Eugene A. Fitzgerald., Massachusetts Institute of Technology. Dept. of Materials Science and Engineering., Massachusetts Institute of Technology. Dept. of Materials Science and Engineering. |
| Publisher | Massachusetts Institute of Technology |
| Source Sets | M.I.T. Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 188 p., 2629996 bytes, 2629752 bytes, application/pdf, application/pdf, application/pdf |
| Rights | M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission., http://dspace.mit.edu/handle/1721.1/7582 |
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