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Proceedings Paper

Micromachined optical concentrators for IR LEDs
Author(s): Geoff R. Nash; Tim Ashley; David T. Dutton; Neil T. Gordon; T. J. Phillips
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Paper Abstract

One of the most important factors limiting the optical efficiency of LEDs is total internal reflection of generated light, where photons incident to the surface at angles greater than the critical angle are reflected back into the semiconductor and absorbed. Most semiconductors have a large refractive index and hence a small critical angle. Narrow gap semiconductors, such as InSb, have particularly large refractive indexes and corresponding smaller critical angles. Additionally, strong absorption of light in the 3-5(mu) m range means that epoxy immersion lenses, which are used for GaAs Ir LEDs, cannot be used in InSb based IR LEDs. We have therefore used a novel micromachining technique to fabricate optical concentrators inInSb and HgCdTe layers. Inductively coupled plasma (ICP) etching is used to alternatively eatch the resist mask and the semiconductor, with oxygen and methane/hydrogen respectively, producing concentrators with parabolic profiles. Continuing optimization of the process to reach the theoretical limits of optical gain is described together with some of the main issues associated with the fabrication process.

Paper Details

Date Published: 18 August 2000
PDF: 6 pages
Proc. SPIE 4179, Micromachining Technology for Micro-Optics, (18 August 2000); doi: 10.1117/12.395681
Show Author Affiliations
Geoff R. Nash, Defence Evaluation and Research Agency Malvern (United Kingdom)
Tim Ashley, Defence Evaluation and Research Agency Malvern (United Kingdom)
David T. Dutton, Defence Evaluation and Research Agency Malvern (United Kingdom)
Neil T. Gordon, Defence Evaluation and Research Agency Malvern (United Kingdom)
T. J. Phillips, Defence Evaluation and Research Agency Malvern (United Kingdom)


Published in SPIE Proceedings Vol. 4179:
Micromachining Technology for Micro-Optics
Sing H. Lee; Eric G. Johnson, Editor(s)

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