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I. Introduction Computers run our everyday lives. Without computers, the idea of launching rockets into space would be unimaginable. Many of the advanced robots that run assembly plants and perform delicate surgery would not exist. Fortunately, computers do exist, and because of them, many things that would not be possible, are II. Semiconductors A semiconductor is a solid or liquid material that can conduct electricity more readily than an insulator, but less easily than a metal. Electrical conductivity, the ability to conduct electrical current under the application of voltage, has one of the widest ranges of values of any physical property of matter. Metals such as copper, silver, gold, and aluminum are excellent conductors, but insulators such as diamond, glass, and rubber are poor conductors. At a low temperature a semiconductor will act as an insulator. However, under the addition of light, heat or other impurities, the conductivity of a semiconductor, can be increased drastically, reaching conductivity levels close to those of metals. The increase in conductivity comes from an increase in the number of conduction electrons, which are the carriers of the electrical current. The common semiconductor is made of chemical elements and compounds such as silicon, germanium, selenium, gallium arsenide, zinc selenide, and lead telluride. III. Transistors A. Introduction to the Transistor The invention of the transistor in 1948 by John Bardeen, W. H. Brattain, and William Shockley of the Bell Telephone Laboratories could be considered the turning point in the history of electronics. At the time transistors looked promising, but they still had their shortcomings. They could not be produced reliably or with predictable electrical characteristics. They were noisy, and they could not operate at frequencies above a few megacycles per second. Three more years of work at the Bell South Laboratory removed most of the early doubts and objections. Transistors can now be made so that their performance is within twenty percent of specifications. B. Background Transistors are made from a crystalline semiconducting material, usually geranium. The number of atomic electrons in this material does not quite match the amount needed to create the normal crystal lattice. If there are a few extra electrons, then the extra electrons can travel through the crystal as readily as free electrons move around the empty space of a vacuum tube. If there is a shortage of electrons, then the “hole” representing the vacant electron sites also travels freely through the crystal. At barriers between areas with plenty of electrons, and areas with not enough electrons of the geranium, the flow of electrons or holes can be controlled by an applied signal.
Approximate Word count = 1638
Approximate Pages = 6.6
(250 words per page double spaced)
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