Каширский 434-2004

better conductors as their temperature rose. Ferdinand Braun discovered that the contact between a metal wire and the mineral galena was rectifying - it would conduct electricity in one direction. Braun also discovered the tuned electrical circuit, which makes it possible to receive a single radio wave. The name of this invention was the Cat's Whisker detector. Semiconductor research really took off in the 20th century when in 1947 John Bardeen. Walter Brattain, and William Shockley of Bell invented the bipolar junction transistor. Semiconductor research has now sparked a revolution in the electronics industry. Semiconductors create cheaper, smaller, faster, and more reliable circuits, and consume less power. Early transistors were produced using germanium because germanium purification was the best developed. In 1958. Jack Kilby of Texas Instruments Incorporated invented the integrated circuit. Also, at the same time but independently from Jack Kilby, Robert Noyce and Jean Hoerni invented the integrated circuit.

There are many different types of semiconductors that exist. Semiconducting materials have a crystal structure. The simplest is the elemental semiconductor, such as Silicon and other group IV elements. In a silicon crystal the atoms are covalently and tetrahedrally bonded and look like this: Semiconductor can also be made of binary compounds, and can also be formed from elements from groups III and V, such as GaAs, from groups II and VI, such as ZnS, or even groups I and VII, such as CuCl. Typical semiconductors, such as silicon, have a symmetrical structure. In nature, two tetrahedra are arranged in a diamond lattice where the base triangles are rotated by 60 degrees, so the top and bottom triangles are staggered. Silicon is very hard and has a high melting point. Without any direct excitation Silicon is a very poor conductor, but acts as an insulator. That's the great thing about semiconductors; they can do both. In order to conduct electricity in silicon there has to be a current; therefore there must be a free electron or a hole able to move around the crystal. There are basically two categories of semiconductors: intrinsic

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Состав semiconductors and extrinsic semiconductors. Elemental semiconductors fall into the intrinsic semiconductor category. An intrinsic semiconductor has no dopants and no lattice defects. It is a "pure" semiconductor. Electrons are thermally excited into a different energy levels, creating electron flow and also current. Electrical current flow results from the net movement of charged carriers. In semiconductors, a completely filled valence band at О К is separated from a completely unfilled conduction band by the band gap. An extrinsic semiconductor contains lattice defects. It is an impure semiconductor. Current is created by "doping" the semiconductor with impurities. Doping semiconductors will change the number of electrons in the crystal. In the case of Silicon, dopants come from group III (В, Al, Ga,...) or group V (P, As, Sb,...). Group III elements will produce a hole because group III elements have one less electron than silicon, these are also known as p-type semiconductors. This hole or acceptor is able to "move" around like a positively charged particle. A new level is created called an acceptor level, which lies close to the valence band (Ea in the picture below). Group V elements will create an extra, free electron because group V elements have one more electron than silicon. The extra electron is called a donor. New levels are also created in this situation called donor levels (Ed in picture below). The free electron moves freely through the crystal and it produces a negative charge. These are called n-type semiconductors. Doped semiconductors still will not conduct current at room temperature.

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