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Germanium infrared absorption chopper

Record type: Conference or Workshop Item (Paper)

The use of Pyroelectric array detectors in Infrared cameras in the 8 to 14µm region necessitates a means for area-modulation, or chopping of the infrared scene, thus generating an element of change for measurement by the detector. Currently this is achieved by mechanically chopping the image using a rotating blade, with drawbacks of high electric motor power, blurring as camera motion changes the rotational speed, and the chopper blade largely determining the camera diameter. Adequate modulation using a novel method has been achieved in the 8 to 14µm region by introducing moderate levels of excess carriers to suitably prepared Germanium. These were introduced via excitation from a diode laser source.
The process described uses inter valence band trasitions from the light-hole to heavy-hole band, requiring power densitities in the order of Watts cm from an AlGaAs 809nm laser is easily achievable. The on state transmission will then be then increased to essentially 100% by using anti-reflection coatings. We will describe the relative importance of the bulk and surface properties; high bulk purity and low surface recombination velocities being required to make an effective device, although operation is possible with lower quality material. The most suitable material for the device is low carrier density n-Germanium.
The modulator does not operate in the much-publicised intra-band transition region which involves generating a free carrier density greater than the critical density, typically requiring laser powers in the order of MW cm.

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Citation

Fairley, P.D. and Rutt, H.N. (1997) Germanium infrared absorption chopper At Semiconductor and Integrated Optoelectronics Conference (SIOE '97), United Kingdom. 24 - 26 Mar 1997.

More information

Published date: 1997
Venue - Dates: Semiconductor and Integrated Optoelectronics Conference (SIOE '97), United Kingdom, 1997-03-24 - 1997-03-26

Identifiers

Local EPrints ID: 76704
URI: http://eprints.soton.ac.uk/id/eprint/76704
PURE UUID: 5c101971-bd38-4a85-9fe5-e2deaf6e0df6

Catalogue record

Date deposited: 11 Mar 2010
Last modified: 18 Jul 2017 23:38

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Contributors

Author: P.D. Fairley
Author: H.N. Rutt

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