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Title page for ETD etd-12152006-111833


Type of Document Dissertation
Author Liang, Di
URN etd-12152006-111833
Title High-Index-Contrast Ridge Waveguide Devices for Integrated Photonic and Optoelectronic Applications
Degree Doctor of Philosophy
Department Electrical Engineering
Advisory Committee
Advisor Name Title
Carol Tanner Committee Chair
Debdeep Jena Committee Member
Douglas Hall Committee Member
Gregory Snider Committee Member
Patrick Fay Committee Member
Keywords
  • integrated optoelectronics
  • materials processing
  • high-index-contrast
  • semiconductor waveguides
  • semiconductor lasers
Date of Defense 2006-12-01
Availability restricted
Abstract
High index contrast (HIC) optical waveguides permit a move towards very large scale integration of photonic integrated circuits (PICs), primarily because of the very small waveguide bending radius achievable. A novel self-aligned fabrication process combining conventional dry etching and a unique non-selective (i.e., Oxygen-enhanced) wet thermal oxidation technique for GaAs-based heterostructures is demonstrated in which a layer of native oxide is formed on the sidewall and base of an etch-defined mesa, largely simplifying the fabrication by simultaneously providing both electrical insulation (eliminating the need for a deposited dielectric and additional mask step) and effective optical mode confinement. Oxidation smoothing, a new technique allowing ultra-low loss HIC waveguides, is demonstrated for the first time in III-V compound semiconductor heterostructures via non-selective oxidation. Excellent device performance (low threshold current, high efficiency, stable-mode operation) is achieved for 808 nm graded-index separate confinement heterostructure (GRINSCH) HIC laser diodes in both straight and curved geometries, indicating a low surface state density at the semiconductor/oxide interface. A record small (r=10 micron) radius half-racetrack-ring resonator laser diode patterned by conventional photolithography is demonstrated. A strong lateral optical confinement factor also leads to a 1.39 micron wide aperture laser with

a nearly symmetric output beam, showing the great potential of the HIC laser structure to overcome longtime limitations in edge-emitting lasers of asymmetric beam divergence and large astigmatism. Detailed stripe width dependent studies also highlight the tremendous performance improvement due to the elimination of current spreading by the HIC structure. As the most critical factor for active devices, interface passivation is qualitatively studied by varying the native oxide thickness, comparing native oxides with conventional plasma-enhanced chemical vapor deposition (PECVD) Silicon Dioxide, and conducting an initial reliability test on an unbonded straight laser. Wet thermal oxidation is also demonstrated for the first time on 1.3 micron dilute-nitride and mid-IR quantum cascade laser (QCL) structures with Al-free active regions, with enhanced dilute-nitride laser performance achieved. Potential benefits of the oxide-confined HIC structure for high-power laser diode bars and other devices are also addressed. The simplified HIC laser fabrication process developed in this work also shows the great potential of non-selective oxidation for future high density PICs.

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