Braun is better known for his development of the cathode ray tube (CRT) oscilloscope in 1897, known as the “Braun tube” (Braunsche Röhre in German). The common descriptive name “cat’s-whisker” detector is derived from the fine metallic probe used to make electrical contact with the crystal surface. He had discovered the rectification effect at the point of contact between metals and certain crystal materials.īraun demonstrated this semiconductor device to an audience at Leipzig on November 14, 1876, but it found no useful application until the advent of radio in the early 1900s when it was used as the signal detector in a “crystal radio” set. When he probed a galena crystal (lead sulfide) with the point of a thin metal wire, Braun noted that current flowed freely in one direction only. In 1874, the German physicist Ferdinand Braun (see the nearby portrait), a 24-year old graduate of the University of Berlin, studied the characteristics of electrolytes and crystals that conduct electricity at Würzburg University. He also found that the effect was not due to temperature variation.įerdinand Braun discovered the rectification effect at the point of contact between metals and certain crystal materials. But when the cover was removed, the conductivity increased. When glasses of various colors were placed in the way of light, the resistance varied according to the amount of light passing through the glass. When the selenium bars were put inside a box with the sliding cover closed, the resistance was the highest. Then Smith discovered that the resistance actually depended on the intensity of incident light. Various experimenters measured the resistance of selenium bars, but the resistance as measured by them under different conditions did not agree at all. He set into experiments with selenium for its high resistance, which appeared suitable for his submarine telegraphy. He was initially working with submarine cables. In 1873, the English electrical engineer Willoughby Smith (1828-1891) (see the nearby portrait) arrived at the discovery of photoconductivity of selenium. Willoughby Smith discovered that resistance actually depended on the intensity of incident light. Photovoltage was generated at the Ag/AgCl metal semiconductor contact. Illumination of the electrode generated photovoltage that altered the EMF produced by the cell, in fact, it produced a reductive (cathodic) photocurrent at the AgCl coated electrode this was the first reported photovoltaic device. In his experiment, a AgCl coated platinum electrode was immersed in an aqueous nitric acid electrolyte solution.
In 1839, he reported the observation of photovoltage in the silver chloride coated platinum electrodes. The next significant contributor to semiconductor field is the French experimental physicist Edmond Becquerel. Quick Facts Created DecemCreator William Shockley, John Bardeen, Walter Brattain Original Use To amplify or switch electronic signals Cost $1 in 1960 – about $8 today Braun discovered that current flowed freely in just one direction at the contact between a metal point and a galena crystal. Karl Braun found and described the first semiconductor diode effect in 1874. The electrical resistance of silver sulfide decreases with temperature, according to Faraday. Michael Faraday was the first to notice a semiconductor effect.
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