Design and characterization of semiconductor laser structures for hydrogen sensing applications

As gas prices continue to rise and fossil fuels pollute our environment, various alternative fuel sources are being actively pursued. Hydrogen shows considerable promise due to its virtually unlimited supply, energy conversion efficiency, and potentially neutral impact on the environment. However, due to the flammability of hydrogen gas in concentrations as low as 4% in air, reliable sensors capable of detecting small concentrations of hydrogen with quick response times are a necessity. Photonic-based gas sensors have a wide assortment of advantages over other sensing mechanisms due to their high sensitivity and quick response time. Therefore, several platforms in which semiconductor lasers can be functionalized to detect hydrogen concentrations below the lower explosive limit have been developed. The laser structures were chosen such that there already exist well-established fabrication technologies, and the functionalization method was designed to be easy, practical, and inexpensive so that these devices can be mass produced using existing technologies. Four different types of hydrogen sensors utilizing thin films of palladium integrated within the structures of semiconductor lasers have been studied. This study includes the design, simulation, fabrication, characterization, and optimization of the devices. The palladium catalyst layer is well known to react to hydrogen gas, forming palladium hydride with optical properties dependent on the hydrogen concentration. This reaction yields a change in complex refractive index and thus also the laser’s output power and peak wavelength. The advantages of these sensors are their small size, high sensitivity, wide dynamic range, inline integration, and scalability to arrays. This thesis is organized into four sections. First, a brief analysis of the rising importance of hydrogen energy sources is presented, followed by an overview of the current state of hydrogen sensing technologies discussing the advantages and disadvantages of each method. Then, a description of the testing setup and procedure common to all device types is presented. Afterward, an in-depth overview is presented of each of the sensors in terms of the device designs, simulation methods and results, fabrication processes, and experimental measurement results. Finally, comparisons of these device designs are offered and conclusions are made.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2013

Author dc:creator

• Griffin, Benjamin G.

Contributors dc:contributor

• Goddard, Lynford L.
• Choquette, Kent D.
• Carney, Paul S.
• Liu, Gang Logan

• Lasers
• Laser Sensing
• Laser Fabrication
• Hydrogen Sensing
• Palladium
• Photonic Crystals
• Vertical Cavity Surface Emitting Lasers (VCSELs)
• Vertical-Cavity Lasers
• Distributed Bragg Reflector (DBR) Lasers
• Distributed Feedback (DFB) Lasers

Statement dc:rights

• Copyright 2013 Benjamin Griffin

Language dc:language

en

Handle dc:identifier

http://hdl.handle.net/2142/44428

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/44428