Page 39 - Chalcogenide Glasses for Infrared Optics

18 Cha pte r T w o

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silicon-arsenic-tellurium system was mapped out by Hilton and Brau.
This development led to an exploratory DARPA- ONR program at TI,
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funded from 1962 to 1965. The ultimate goal of the program was to
find infrared transmitting chalcogenide glasses with physical proper-
ties comparable to those of oxide optical glasses and a softening point
of 500°C. An attempt was made to achieve this goal by incorporating
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transition element titanium in the composition. Further work was
funded on sulfur-based glasses in 1973 to 1974. The exploratory pro-
grams resulted in eight chalcogenide glass U.S. patents. Three papers
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were published in an international journal detailing the results. As
a result of publishing the three papers, the author was invited to
present a paper at the Fourth All-Union Symposium on the Vitreous
Chalcogenide Semiconductors held in May 1967 in Leningrad (now
called St. Petersburg). While at the meeting, the author met Valentina
Kokorina, head of the Russian chalcogenide glass production facility.
Valentina Kokorina, now retired, recently published a book detailing
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the Russian effort. Representing the West also was Prof. Douglas
McKenzie of the University of California, Los Angeles, a well-known
glass scientist. From the University of Edinburgh in Scotland was
Prof. Alan Owen, head of the Electrical Engineering Department.
Another from the West at the meeting was Stanley Ovshinsky, founder
of Electron Energy Conversion Devices in Troy, Michigan, who pre-
sented his first paper advocating switching devices based on the elec-
tronic properties of chalcogenide glasses. Similar work in the United
States was reported earlier by A. David Pearson of Bell Telephone
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Laboratories. Thus started a great worldwide effort to investigate
chalcogenide glasses and their electronic properties. The purpose
was to pursue a new family of inexpensive electronic devices based
on amorphous semiconductors. The effort in this field far exceeded
the effort directed toward optical applications. Some of the results of
the efforts in the United States were reported in a symposium in
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1969 and in another symposium in 1971. Generally, the glasses
used could be made conducting with applied voltage resulting in the
formation of a crystalline filament path. Such glasses were not suit-
able for optical use and are not discussed in this book. Our discussion
concentrates on efforts in the United States to develop infrared opti-
cal materials, specifically, chalcogenide glasses from groups IVA, VA,
and VIA from the periodic table.
In 1966, the Air Force decided to fund a Research Program on
Infrared Optical Materials at Central Research Laboratories at TI.
There was a six-month delay in funding. During this time, Robert
Patterson mapped out the glass forming region for the germanium-

antimony-selenium system. A U.S. patent was granted covering the
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best composition selected, TI 1173.
When the author returned to the United States in 1967 and reported
the existence of a chalcogenide glass production facility in Russia the
Air Force decided to fund a Development Program at TI with a goal of