semiconductor

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.