Antimonide-based mid-infrared light-emitting diodes for low-power optical gas sensors

Meriggi, Laura (2015) Antimonide-based mid-infrared light-emitting diodes for low-power optical gas sensors. PhD thesis, University of Glasgow.

Due to Embargo and/or Third Party Copyright restrictions, this thesis is not available in this service.

Abstract

The 3-5 μm mid-infrared spectral region is of great interest as it contains the fundamental
molecular fingerprints of a number of pollutants and toxic gases, which require
remote real-time monitoring in a variety of applications. Consequently, the development
of efficient optoelectronic devices operating in this wavelength range is a very fascinating
and pertinent research. In recent years, there has been a rapid development of optical
technologies for the detection of carbon dioxide (CO2), where the detected optical intensity
at the specific gas absorption wavelength of 4.26 μm is a direct indication of the gas
concentration, the main applications being in indoor air quality control and ventilation
systems. The replacement of conventional infrared thermal components with high performance semiconductor light-emitting diodes (LEDs) and photodiodes in the 3-5 μm
range allows to obtain sensors with similar sensitivity, but with an intrinsic wavelength
selectivity, reduced power consumption and faster response. Gas Sensing Solutions Ltd.
has developed a commercial CO2 optical gas sensor equipped with an AlInSb-based
LED and photodiode pair, which has demonstrated a significant reduction in the energy
consumption per measurement.

The aim of this Ph.D. project, supported by an EPSRC Industrial CASE Studentship,
was to improve the performance of mid-infrared AlInSb LEDs. This was achieved
through the optimisation of the layer structure and the device design, and the application
of different techniques to overcome the poor extraction efficiency (~ 1 %) which
limits the LED performance, as a consequence of total-internal reflection and Fresnel
reflection. A key understanding was gained on the electrical and optical properties of
AlInSb LEDs through the characterisation of the epi-grown material and the fabrication
of prototype devices. Improved LED performance, with a lower series resistance and
stronger light emission, was achieved thanks to the analysis of a number of LED design
parameters, including the doping concentration of the contact layers, the LED lateral
dimensions and the electrode contact geometry. A Resonant-Cavity LED structure was
designed, with the integration of an epitaxially-grown distributed Bragg reflector between
the substrate and the LED active region. The advantage of this design is twofold,
as it both redirects the light emitted towards the substrate in the direction of the top
LED surface and adds a resonant effect to the structure, resulting in a three-times
higher extraction efficiency at the target wavelength of 4.26 μm, spectral narrowing and
improved temperature stability. Finally, 2D-periodic metallic hole array patterns were
integrated on AlInSb LEDs, showing potential advantages for spectral filtering and enhanced
extraction of light emitted above the critical angle.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: mid-infrared, light-emitting diodes, antimonides, resonant-cavity, optical gas sensing
Subjects: T Technology > T Technology (General)
T Technology > TK Electrical engineering. Electronics Nuclear engineering
Colleges/Schools: College of Science and Engineering > School of Engineering > Electronics and Nanoscale Engineering
Supervisor's Name: Sorel, Professor Marc
Date of Award: 2015
Embargo Date: 9 October 2018
Depositing User: Laura Meriggi
Unique ID: glathesis:2015-6691
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 09 Oct 2015 09:08
Last Modified: 09 Oct 2017 08:16
URI: http://theses.gla.ac.uk/id/eprint/6691

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