![]() ![]() The junction and the different regions of impurity also allowed it to respond to light. ![]() The area where this region joined the rest of the silicon formed a “junction.” This junction had something to do with the diode action of the device. Eventually, however, they determined that the sample, which had been cut from a larger piece of silicon, had a region that contained high levels of a certain kind of impurity. He had invented a new type of diode that was also an efficient solar energy converter or “cell.” The reason it worked either as a diode or as a solar cell was a mystery to the researchers. Russell Ohl, a Bell Labs metallurgist working with silicon samples discovered that one of his samples acted like a diode and-even more remarkable-produced electricity in response to light. During the war years, thousands were manufactured, and in the course of research on semiconductors, Bell Laboratories scientists stumbled on a new type of diode. For these reasons the use of cat’s whisker diodes declined, although their ability to work at very high frequencies made them valuable during World War II when they were used in radar receivers. ![]() They required careful adjustment and could easily be knocked out of alignment. In the early 1900s, cat’s whisker diodes were widely used in radio receivers, as they were an improvement over electron tubes. The crystal then acts as a one-way valve for electrical current and can be used to separate a radio signal from its carrier wave. A fine piece of wire-the “cat’s whisker”-is touched on the surface until the “sweet spot” is located. Part of a 1920s cat’s whisker diode that uses a small crystal of the semiconductor galena. Dunwoody patented a version of it that used a material called carborundum. This type of “cat’s whisker” diode (so-named because of the fine wire used in it) became more popular after American H. By placing a silicon crystal between a metal base and a carefully placed fine wire, Pickard created a valve that could also be used to detect radio waves. Pickard based his design on the earlier discovery that electricity can flow in only one direction through certain types of mineral crystals, such as silicon. It came into use for radio transmission and soon became the basis of Lee De Forest’s Audion electron tube, which he invented in 1906.Īlso around 1906, American engineer Greenleaf W. The Fleming valve is remembered as the first true electronic device. In the early 1900s, for example, English engineer John Ambrose Fleming used this one-way electrical “valve,” to convert radio waves into a flow of current that could be measured by a galvanometer. Others found another use for this device. Thomson (1856~1940) announced the discovery of the electron in April 1897 and explained the Edison effect where current travels just one way through a vacuum tube. He was not sure what to do with this discovery, and moved on to other projects. Thomas Edison discovered that including an extra electrode in a light bulb and connecting it to the positive side of a battery resulted in a current flowing from the filament through the empty space. The first diode was a modified light bulb. Both were invented early in the 20th century. The other type uses semiconductors, like the transistor. One is an electron tube similar to the triode. This is useful in converting AC to DC, processing high frequency signals, regulating voltages, and in other applications. Used in all sorts of electrical and electronic systems, the diode functions as a one-way valve for electric current-it only allows current to flow in one direction. ![]() The diode is one of the oldest and most important electronic devices, although it is not as famous as its cousin, the transistor. ![]()
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