views updated May 29 2018

semiconductor Substance with electrical conductivity between that of a conductor and an insulator. The conductivity increases as temperature increases. A semiconductor consists of elements, such as germanium and silicon, or compounds, such as aluminium phosphide, with a crystalline structure. At normal temperatures, some electrons break free and give rise to n-type (negative) conductivity with the electrons as the main carriers of the electric current. The holes (electron deficiencies) left by these electrons give rise to p-type (positive) conductivity with the holes as the main carriers. Impurities are usually added to the semiconductor material in controlled amounts to add more free electrons or create more holes. A semiconductor junction forms when there is an abrupt change along the length of the crystal from one type of impurity to the other. Such a p-n junction acts as a very efficient rectifier, converting alternating current (AC) into direct current (DC), and is the basis of the semiconductor diode. Semiconductors are also used in transistors and photoelectric cells.


views updated May 14 2018

semiconductor A material, such as silicon or germanium, whose electrical conductivity increases with temperature and is intermediate between metals and insulators. In pure semiconductors this effect is due to the thermal generation of equal numbers of negative charge carriers (electrons) and positive charge carriers (holes). These materials are called intrinsic or i-type semiconductors.

The introduction of specific types of impurity atoms into a pure semiconductor can significantly increase its conductivity: donor impurities, which belong to group 5 of the periodic table, greatly increase the number of conduction electrons and produce an n-type semiconductor; acceptor impurities, which belong to group 3, greatly increase the number of holes and produce a p-type semiconductor. These materials are called extrinsic semiconductors. The conductivity of an extrinsic semiconductor depends on the type and the amount (or doping level) of impurity present.

Semiconductors of different conductivity – n-type, p-type, highly doped n- and p-type, i-type – can be brought together to form a variety of junctions, which are the basis of semiconductor devices used as electronic components. The term semiconductor is frequently applied to the devices themselves.


views updated Jun 11 2018

sem·i·con·duc·tor / ˈsemēkənˌdəktər; ˈsemˌī-/ • n. a solid substance that has a conductivity between that of an insulator and that of most metals, either due to the addition of an impurity or because of temperature effects. Devices made of semiconductors, notably silicon, are essential components of most electronic circuits.