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Proceedings Paper

Optimizing indium aluminum antimonide LEDs and photodiodes for gas sensing applications
Author(s): Harvey R. Hardaway; Tim Ashley; Louise Buckle; Martin T. Emeny; Graeme Masterton; Graham Pryce
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Paper Abstract

We have developed a range of un-cooled mid-IR LEDs and photodiodes for IR gas sensing applications. Varying the composition of MBE grown Indium Aluminium Antimonide (In(1-x)AlxSb) epi-layers on GaAs allows us to engineer the emission/detection wavelength for a particular gas up to λmax≈6μm. The relatively high series resistance, LED drive requirements, and the non-optimised impedance matching of the un-biased photodiodes restricts the market for these components. Sub-dividing single element devices into N smaller devices connected in series enable the LED current and voltage requirements to be tailored to match the source, and improves the photodiode impedance matching. We report the development of the necessary growth and photolithography technologies for series-connecting InAlSb diodes on GaAs substrates. We include results from multi-element Co2 (Al(x)=4.5%) and CH4 (Al(x)=8.5%) sensing LEDs and photodiodes. These impedance matched LEDs represent a 9-fold improvement in the wall-plug efficiency compared with single element LEDs with the same light output. The impedance of the multi-element photodiodes is increased significantly with respect to the series resistance, which gives up to a 5-fold improvement in sensitivity since the noise contributions from the external amplifier and series resistance are minimised. These advances have greatly improved the suitability of these components for gas sensing, and further improvements in the performance are expected through optimisation of the epi-layer design and the device geometry.

Paper Details

Date Published: 22 October 2004
PDF: 8 pages
Proc. SPIE 5564, Infrared Detector Materials and Devices, (22 October 2004); doi: 10.1117/12.560577
Show Author Affiliations
Harvey R. Hardaway, QinetiQ (United Kingdom)
Tim Ashley, QinetiQ (United Kingdom)
Louise Buckle, QinetiQ (United Kingdom)
Martin T. Emeny, QinetiQ (United Kingdom)
Graeme Masterton, QinetiQ (United Kingdom)
Graham Pryce, QinetiQ (United Kingdom)


Published in SPIE Proceedings Vol. 5564:
Infrared Detector Materials and Devices
Randolph E. Longshore; Sivalingam Sivananthan, Editor(s)

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