Q. What is Pure semiconductors?
Pure semiconductors, known as intrinsic semiconductors, have very few charge carriers and may hence be classified as almost insulators or very poor electrical conductors. However, by adding (through a process known as doping) tiny controlled amounts of impurities (such as boron, gallium, indium, antimony, phosphorus, or arsenic), a semiconductor can be made to contain a desired number of either holes or free electrons and is then known as extrinsic (impure) material. A p-type semiconductor contains primarily holes, whereas an n-type semiconductor contains primarily free electrons. While holes are the majority carriers in a p-type material, it is possible to inject electrons artificially into p-type material, in which case they become excess minority carriers. Minority carriers do play a vital role in certain devices. The doping substance is called an acceptor when the extrinsic semiconductor is the p-type with holes forming the majority carriers and electrons forming the minority carriers. The doping substance is known as the donor when the extrinsic semiconductor is the n-type with free electrons forming the majority carriers and holes forming the minority carriers. Both p- and n-type semiconductors are vitally important in solid-state device technology. Diodes, transistors, and other devices depend on the characteristics of a pn-junction formed when the two materials are joined together as a single crystal.