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Invention of the Point Contact Transistor, 1954

One Way

A diode, otherwise known as a "rectifier," is a device through which electricity can flow in only one direction. The earliest diodes were made of crystal and were used in home radio kits to direct radio signals. A fine wire known as a "cat's whisker" was used to feed a weak radio signal into the crystal, and the crystal then removed the high frequency radio carrier signal. This allowed the part of the signal carrying the audio information to come through, and thus signals carrying news and music could be heard.

Crystals contain impurities, making some sections more resistant to electrical flow than others. In 1939, scientist Russell Ohl discovered that it was the boundary between sections of different purity that enabled the crystal to direct electricity in one direction. Each "side" of the boundary was a semiconductor, and some semiconductors carried electricity more easily than others. After this discovery was made, diodes were constructed with two sides, separated by a boundary. One side was made up of a semiconductor that carried electrons easily, and the other side of a semiconductor that did not carry electrons easily. Electrons jumped easily from the side that did not carry electrons easily to the side that did. Electricity was thus conducted successfully in only one direction.

The discovery of the boundary between semiconductors with different levels of conductivity made a key contribution to the development of the transistor. You can read a report on the transistor which includes information released by Bell Laboratories by clicking on the thumbnails at right.