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In 1876, a German scientist, Ferdinand Braun, discovered that the behaviour of galena (lead sulfide), depended on the nature of the connection made to it. Large area connections behaved very differently from those made using a fine point contact. Braun found that with a point contact the resistance of the junction depended on which way round the battery was connected. We call this property rectification and the device he created is called a diode.

Galena is a semiconductor with a small bandgap of about 0.4 eV which found use in early wireless communication systems. For example, it was used as the crystal in crystal radio sets, in which it was used as a point-contact diode to detect the radio signals. The galena crystal was used with a safety pin or similar sharp wire, which was known as a "cat’s whisker". Making such wireless sets was a popular home hobby in Britain and other European countries during the 1930s. (en.wikipedia.org/wiki/Galena)


"The sulfides galena, chalcopyrite, and pyrite are semiconductors whose electrical resistivity and type are controlled by deviations from stoichiometry and impurity content, and hence by their geochemical environment.

Spurious thermoelectric voltages on polished surfaces of galena, due to the polishing process, have been documented by Granvilleand Hogarth (1951).

Tauc (1953) suggested that these were due to electrically charged mechanical damage in a surface layer." (from: The electrical resistivity of galena, pyrite, and chalcopyrite", Doneln F. Pnlorrronr eNn RnlpH T. Suurv

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from Electrochemical, photoresistive and photomagnetic properties of semiconductors, released July 29, 2014

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