semiconductor

semiconductor solid material whose electrical conductivity at room temperature is between that of a conductor and that of an insulator (see conduction ; insulation ). At high temperatures its conductivity approaches that of a metal, and at low temperatures it acts as an insulator. In a semiconductor there is a limited movement of electrons, depending upon the crystal structure of the material used. The substances first used for semiconductors were the elements germanium, silicon, and gray tin. It was found that the incorporation of certain impurities in them enhances their conductive properties. The impurities either add free electrons or create holes (electron deficiencies) in the crystal structures of the host substances by attracting electrons. Thus there are two types of semiconductor: the N-type (negative), in which the current carriers (electrons) are negative, and the P-type (positive), in which the positively charged holes move and carry the current. The process of adding these impurities is called doping; the impurities themselves are called dopants. Dopants that contribute mobile electrons are called donor impurities; those that cause holes to form are acceptor impurities. Undoped semiconductor material is called intrinsic semiconductor material. Certain chemical compounds, including gallium arsenide, indium antimonide, and aluminum phosphide are semiconductors. Semiconductors are used to produce such electronic devices as diodes , transistors , and computer memory devices. The field of solid-state physics includes the study of semiconductors. See also integrated circuit .

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.