Injected Light Emission of Silicon Carbide Crystals by K. LEHOVEC, C. A. Accardo, AND E. JAMGOCHIAN

An overview of this paper from a 1998 letter to Dr. Richard Bingham by Dr. Carl Accardo
The second project in which I was associated was a series of experiments dedicated to the explanation of a "cold" light phenomena first observed in silicon carbide in 1907 (see attached abstract by H.J . Round) . This effect, which was manifested by passing current through selected crystals of silicon carbide, showed a type of light emission which remained unexplained until 1950. An attempt to explain the light had been proposed in the 1940's by a Russian researcher named O.W. Lossev. Dr. Kurt Lehovec, a Czech scientist also working at Camp Evans approached me to inquire if I would be interested in studying the effects with him and his co-worker Edward Jamgochian. Our research indicated that the light produced was due to the recombination of electrons and holes across a so-called p-n junction.
The two articles authored by Lehovec, myself and Jamgochian appeared in Physical Review magazine in 1951, and 1952 (these are attached) and also was presented at the American Physical Society in New York. The articles provided an explanation of what later became known as LED's, or light emitting diodes. Today, it is acknowledged that the papers were the pioneering ones (see attached paragraph appearing in book by C.H . Gooch, titled, Injection Electroluminescent Devices) . The search for a compound semiconductor in which detailed control of the fabrication process became possible led to Bell Laboratories development of gallium arsenide LED's which today are found in numerous applications such as display devices, fiber optic communication systems, etc.
Thanks to Dr. Carl A. Accardo for providing a copy of this paper.


Camp Evans Technical Publication The Physical Review Vol. 83, No. 3, 603-607 August 1, 1951 Page 603 - 607	Dr. Kurt Lehovec

Injected Light Emission of Silicon Carbide Crystals

K. LEHOVEC, C. A. ACCARDO, AND E. JAMGOCHIAN
Signal Corps Engineering Laboratories, Fort Monmouth, New Jersey
(Received April 5, 1951)

Recombination of carriers injected throughP-N boundaries in silicon carbide crystals may lead to light
emission ("injected light emission") . This light emission was investigated as a function of temperature
and of current through the crystal by use of a photomultiplier. The emission spectrum extends from
4500A to 6500A at room temperature and is found to be nearly independent of current from 0.1 ma to 50 ma.
The light intensity increases approximately proportionally to current (efficiency about 10-6 quanta per
electron at room temperature for a particular crystal) .


I. INTRODUCTION SOME silicon carbide crystals emit "cold" light while current passes. 1-7 Two types have been reported : (a) a bluish light and (b) a yellow light, the type emitted depending on the direction of current flow. The parts of the crystal that emit yellow light do not coincide, in general, with those emitting blue light on current reversal ; nor does the same crystal necessarily emit both types. We conclude that the mechanism of excitation differs for the two cases. Previously published data on the intensity and spectral distribution of the light are of a qualitative nature. In this paper quantitative information is pre- --------------- 1 O. Lossew, Wireless World and Radio Review 271, 93 (1924) 2 O. Lossew, Z. Fernmeldetechnik 7, 97 (1926) . 3 O. Lossew, Phil . Mag. 6, 1028 (1928) . 4 O: Lossew, Physik. Z. 30, 920 (1929) . . 5 O. Lossew, Physik. Z. 32, 692 (1931) . 6 O. Lossew, Physik. Z. 34, 397 (1933) . 7 B. Claus, Ann. Physik 11, 331 (1931) .	sented on the spectral distribution of the yellow light and its dependence on current density and temperature.

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