IX. History o' Diodes

Tom Lee [mailto:tomlee@ee.stanford.edu] writes:

Sent: Wednesday, March 24, 1999 7:35 PM
To: mjc@avtechpulse.com
Subject: About ancient diodes

As far as I know, the earliest paper on asymmetrical conduction was written by Karl Ferdinand Braun in 1874 ("Ueber die Stromleitung durch Schwefelmetalle (On current flow through metallic sulfides)," Poggendorf's Annalen). He discovered that galena (lead sulfide) and copper pyrites, among others, could rectify. Of course, these experiments predated radio, so application of Braun's discoveries to wireless communication took a couple more decades. Perhaps the first to apply semiconductor diodes to the radio art was the remarkable Jagadis Chandra Bose, who applied for a patent on a galena detector in 1901 (it was finally awarded in 1904). This was used in his research work in the area of millimeter-wave RF!

G.W. Pickard worked harder than anyone else to develop point-contact detectors. He tested over 31,000 combinations of minerals and wires in a search for the "best" detector. He patented a silicon-based point-contact detector in early 1907, and it worked exceedingly well. H.H.C. Dunwoody patented a silicon carbide (carborundum) detector in late 1906, and that device also worked quite well, although a bias was essential for proper operation. In all of these point contact structures, the ohmic contact was made either by immersing the crystal specimen in a low melting-point alloy (Wood's Metal), or simply with a clamp of some sort. The rectifying contact was generally with a very thin wire, whimsically known as a catwhisker. For galena, only the lightest touch was acceptable. Progressively higher pressures were acceptable for iron pyrite (fools' gold), and for carborundum. In all cases, one had to hunt around the mineral surface in search of a suitably sensitive spot.

Galena and iron pyrites are readily available in mineral shops, so a homebrew diode is easily put together. Rusty razor blades have also been known to work, typically with a pencil lead used as catwhisker.

For more information on early point-contact diodes, I highly recommend the following two articles:

A. Douglas, "The Crystal Detector," IEEE Spectrum, April 1981, pp. 64-7.

D. Thackeray, "When Tubes Beat Crystals: Early Radio Detectors," IEEE Spectrum, March 1983, pp.64-9.

I have much more information than I've provided here, but this is probably enough for now.

Tom Lee
Asst. Prof. of Elect. Eng.
Stanford University
http://www-smirc.stanford.edu

Ralph Muha [ralph@ycrdi.com] notes that:

Antique electronics (http://www.tubesandmore.com) sells mounted galena (lead sulfide) crystals for use in crystal sets, item P-Q111 for $2.25... You can also get phosphor bronze cat's whiskers (P-H415, $2.25 for a package of 3). 

For diode history buffs, a "popular history" is available:

Crystal Fire : The Birth of the Information Age (Sloan Technology Series) by Michael Riordan, Lillian Hoddeson
Hardcover - 352 pages 1 Ed edition (August 1997)
W.W. Norton & Company; ISBN: 0393041247

For the academically oriented, I highly recommend:

Semiconductor Devices : Pioneering Papers, S.M. Sze (Editor)
Paperback (February 1991) World Scientific Pub Co; ISBN: 9810202105