semiconductor

Experimentation on the identification and use of semiconductors began in the late 1940s. Progress in the field enabled radios during the 1960s to lose their bulky vacuum tubes (valves) and instead use transistors. It is because silicon is an excellent semiconductor that it is now commonly used in electronic (silicon) chips.

Material with electrical conductivity intermediate between metals and insulators and used in a wide range of electronic devices. Certain crystalline materials, most notably silicon and germanium, have a small number of free electrons that have escaped from the bonds between the atoms. The atoms from which they have escaped possess vacancies, called holes, which are similarly able to move from atom to atom and can be regarded as positive charges. Current can be carried by both electrons (negative carriers) and holes (positive carriers). Such materials are known as intrinsic semiconductors.

Conductivity of a semiconductor can be enhanced by doping the material with small numbers of impurity atoms which either release free electrons (making an n-type semiconductor with more electrons than holes) or capture them (a p-type semiconductor with more holes than electrons). When p-type and n-type materials are brought together to form a p–n junction, an electrical barrier is formed that conducts current more readily in one direction than the other. This is the basis of the semiconductor diode, used for rectification, and numerous other devices including transistors, rectifiers, and integrated circuits (silicon chips).