A solid substance that allows heat or electricity to pass through it or along it in particular conditions

Asemiconductormaterial has anelectrical conductivityvalue falling between that of aconductor, such as metallic copper, and aninsulator, such as glass. Itsresistancedecreases as its temperature increases, which is behaviour opposite to that of a metal. Its conducting properties may be altered in useful ways by the deliberate, controlled introduction of impurities ("doping") into thecrystal structure. Where two differently-doped regions exist in the same crystal, asemiconductor junctionis created. The behavior ofcharge carrierswhich includeelectrons,ionsandelectron holesat these junctions is the basis ofdiodes,transistorsand all modernelectronics. Some examples of semiconductors aresilicon,germanium,gallium arsenide, and elements near the so-called "metalloid staircase" on the periodic table. After silicon, gallium arsenide is the second most common semiconductor[citation needed]and is used in laser diodes, solar cells, microwave-frequency integrated circuits and others. Silicon is a critical element for fabricating most electronic circuits.

Semiconductor devicescan display a range of useful properties such as passing current more easily in one direction than the other, showing variable resistance, and sensitivity to light or heat. Because the electrical properties of a semiconductor material can be modified by doping, or by the application of electrical fields or light, devices made from semiconductors can be used for amplification, switching, andenergy conversion.

The conductivity of silicon is increased by adding a small amount (of the order of 1 in 108) of pentavalent (antimony,phosphorus, orarsenic) or trivalent (boron,gallium,indium) atoms. This process is known as doping and resulting semiconductors are known as doped or extrinsic semiconductors. Apart from doping, the conductivity of a semiconductor can equally be improved by increasing its temperature. This is contrary to the behaviour of a metal in which conductivity decreases with increase in temperature.

The modern understanding of the properties of a semiconductor relies onquantum physicsto explain the movement of charge carriers in acrystal lattice.[1]Doping greatly increases the number of charge carriers within the crystal. When a doped semiconductor contains mostly free holes it is called "p-type", and when it contains mostly free electrons it is known as "n-type". The semiconductor materials used in electronic devices are doped under precise conditions to control the concentration and regions of p- and n-type dopants. A single semiconductor crystal can have many p- and n-type regions; thep–n junctionsbetween these regions are responsible for the useful electronic behavior.

Some of the properties of semiconductor materials were observed throughout the mid 19th and first decades of the 20th century. The first practical application of semiconductors in electronics was the 1904 development of thecat's-whisker detector, a primitive semiconductor diode used in early radio receivers. Developments in quantum physics in turn allowed the development of thetransistorin 1947,[2]theintegrated circuitin 1958, and theMOSFET(metal–oxide–semiconductorfield-effect transistor) in 1959.

solid substance that allows heat or electricity to pass through it or along it in particular conditions

अर्धचालक (विशिष्‍ट दशाओं में ताप या विद्युत का चालन करने वाला एक ठोस पदार्थ); सेमिकंडक्‍टर