Discovery of Semiconductors
1791-1867 Michael Faraday [Wikipedia]
1833 The First Documented Observation of a Semiconductor
Michael Faraday

In in 1833, he was investigating the effect of temperature on silver sulfide. He found that electrical conductivity increased with increasing temperature. This was opposite of that measured in metals such as copper, of which conductivity decreases as temperature increases. This was the first observation of temperature dependence of electrical conductivity of a semiconductor.

Michael Faraday
Experimental researches in electricity. Fourth series
Philosophical Transactions of the Royal Society of London, Volume 123, pp. 507-522 (1833).

Paragraph 432
The effect of heat in increasing the conducting power of many substances, especially for electricity of high tension, is well known. I have lately met with an extraordinary case of this kind, for electricity of low tension, or that of the voltaic pile, and which is in direct contrast with the influence of heat upon metallic bodies, as observed and described by Sir Humphry Davy [1].

[1] Humphry Davy
Farther researches on the magnetic phaenomena produced by electricity:
with some new experiments on the properties of electrified bodies
in their relations to conducting powers and temperature
Philosophical Transactions of the Royal Society of London, Volume 111, pp. 425-439 (1821).
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