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Proceedings Paper

Optical immersion of mid-infrared LEDs and photodiodes for gas-sensing applications
Author(s): Harvey R. Hardaway; C. T. Elliot; Neil T. Gordon; J. Graham Crowder
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Paper Abstract

The high gains in performance predicted for optical immersion are difficult to achieve in practice due to total internal reflection at the lens/detector interface. By reducing the air gap at this interface optical tunneling becomes possible and the predicted gains can be realized in practical devices. Using this technique we have demonstrated large performance gains by optically immersing mid-infrared heterostructure InA1Sb LEDs and photodiodes using hypershperical germanium lenses. The development of an effective method of optical immersion that gives excellent optical coupling has produced a photodiode with a peak room temperature detectivity (D*) of 5.3 x 109 cmHz½W-1 at λpeak=5.4μm and a 40° field of view. A hyperspherically immersed LED showed a f-fold improvement in the external efficiency, and a 3-fold improvement in the directionality compared with a conventional planar LED for f/2 optical systems. The incorporation of these uncooled devices in a White cell produced a NO2 gas sensing system with 2 part-per-million sensitivity, with an LED drive current of <5mA. These results represent a significant advance in the use of solid state devices for portable gas sensing systems.

Paper Details

Date Published: 11 March 2003
PDF: 7 pages
Proc. SPIE 4947, Laser Diodes, Optoelectronic Devices, and Heterogenous Integration, (11 March 2003); doi: 10.1117/12.468247
Show Author Affiliations
Harvey R. Hardaway, QinetiQ (United Kingdom)
C. T. Elliot, QinetiQ (United Kingdom)
Neil T. Gordon, QinetiQ (United Kingdom)
J. Graham Crowder, Heriot-Watt Univ. (United Kingdom)

Published in SPIE Proceedings Vol. 4947:
Laser Diodes, Optoelectronic Devices, and Heterogenous Integration
John Gerard McInerney; Alfred Driessen; Roel G. Baets; Ephraim Suhir, Editor(s)

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