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Proceedings Paper

New Leddicon target sensitive in the 1000- 2000-nm waveband and beyond
Author(s): G. P. Hopkins; D. G. Swain
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Paper Abstract

There are numerous requirements for inexpensive TV imaging systems to cover the near infra red spectrum out to 2000nm. Applications include covert surveillance, semiconductor inspection, laser and thermal imaging. At the heart of such a system is the image pick-up device: usually in the form of a vacuum tube of the Vidicon type or a solid state sensor array. Unfortunately there are very few photoemissive or photoconductive materials that can be employed as sensors for cameras across the 1000-2000nm band. Image tubes using the Si (Ag/O/Cs) photocathode work to i500nm but have poor sensitivity. Most silicon devices in the form of Vidicon targets or CCDs are not sensitive beyond iiOOnm. Only the PtSi Shottky barrier imagers cover this spectrum, but they are expensive and require cooling to reduce dark currents to tolerable levels. For over 50 years lead suiphide has been used to detect near infra red raaiation to its limit of 3300nm, but because of its low resistivity (iO iO ohm-cm) it cannot store charge information long enough to be useful a3 an imaging material. On the other hand lead oxide has a resistivity (iO ohm-cm) high enough for imaging but its long wavelength detection limit is only 650nm. In i949 Frank and Raithel (i) compromised by combining PbO and PbS in the hope of making a more viable IR photoconductive target. Their method was to evaporate first a PbO film and then subject it to sulphur vapour at elevated temperature followed by further heat treatments. Although the spectral response they obtained extended from the visible to about i800nm the sensitivity was non uniform, dark currents were high and the Image retention was severe. Later work by Heimann and Kunze (2) and Hon et. al. (3) claimed to improve the transient response or lag, but picture qualities still were deemed to be very poor. More recent developments by Kawai (4) extended the spectral limit of their Vidicon to 2700nm by using a very lengthy version of the original Frank and Raithel process. There remained however many practical problems concerned with reproducibility in the production process and the stability of target and tube performance. R Registered Trade Mark of EEV Co. for photoconductive camera tubes with lead oxide targets.

Paper Details

Date Published: 1 October 1990
PDF: 20 pages
Proc. SPIE 1320, Infrared Technology and Applications, (1 October 1990); doi: 10.1117/12.22320
Show Author Affiliations
G. P. Hopkins, EEV Co. (United Kingdom)
D. G. Swain, EEV Co. (United Kingdom)

Published in SPIE Proceedings Vol. 1320:
Infrared Technology and Applications
Alan H. Lettington, Editor(s)

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