Discovery of "pn Junction"In the mid 1930s, electrochemist Russell Ohl of the Bell Telephone Labs facility in Holmdel, New Jersey, started investigating the use of silicon rectifiers as radar detectors. He found that the increase in silicon crystal purity helped improve their ability to detect low voltages. On February 23, 1940 he examined some small silicon wafers, which brought strange and amazing results. The amount of current flowing through the semiconductor layer sharply increased when the crystal was exposed to bright light. He also noticed that different crystal sections had opposing electric potentials while examining the cat's whisker crystals. Russell Ohl and his colleague Jack Scaff found that the crack in the middle of the crystal wafer divides it into areas with different types of impurities. Some impurities (phosphor, for example) caused the excess of electrons in the specimen while others (boron, for example) caused a small deficit of electrons (later dubbed as "electron holes"). The researches called these areas n-types (negative) и р-types (positive); and the dividing barrier became known as the pn junction. Bright light in the junction boosts electrons to move from the n-section to the p-section producing electric current. Ohl discovered photoelectric current that led to the development of solar cells. William Shockley used the concept of the pn junction to develop a transistor in 1948. And the pn junction became one of the most common types of a ...
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