Semiconductors

A semiconductor is a solid whose electrical conductivity lies between that of a conductor and an insulator. Its conductivity can respond to temperature, illumination and even very small amounts of added impurity atoms. In a crystal, electrons occupy energy bands; when electrons gain enough energy to move into a conducting band, they can carry current. The empty places left behind in the lower band behave as positively charged carriers called holes. Both electrons and holes contribute to electrical conduction.

Engineers can adjust a semiconductor’s electrical behavior by adding carefully chosen dopant atoms, a process known as doping. An n-type region has electrons as its majority carriers; a p-type region has holes as its majority carriers. Where these regions meet, they form a p–n junction. The junction’s response to voltage allows current to pass much more readily in one direction than the other, a property used in diodes. More complex arrangements of semiconductor regions make transistors, which can control or amplify electrical signals.

A semiconductor device may be a single component, such as a diode, light-emitting device or sensor, or part of an integrated circuit. Integrated circuits place many interconnected components on one small piece of semiconductor material. Logic chips process information, memory chips store it, and analog chips handle continuously varying signals such as those from sensors. Other devices detect light, manage electrical power or perform a single circuit function. These different jobs mean that semiconductor technology is not one uniform kind of chip.

Silicon became the dominant material for many integrated circuits because it has useful electrical properties and forms a high-quality insulating layer of silicon dioxide. Other materials serve specialized purposes: gallium arsenide is used in some optical and radio-frequency applications, while silicon carbide and gallium nitride can be useful in power electronics that operate at high voltages or temperatures. To manufacture a chip, factories process thin semiconductor wafers through repeated steps that pattern, add, remove or modify material. Photolithography transfers circuit patterns onto wafers; testing and packaging follow fabrication. The complexity of these processes has encouraged specialization among chip designers, manufacturers and assembly and testing firms.

Early observations of unusual electrical behavior in crystals eventually led to practical semiconductor devices. The transistor, demonstrated in 1947, made it possible to amplify or switch signals using a compact solid-state component instead of larger vacuum-tube equipment. Integrated circuits then combined multiple components on a chip, enabling increasingly complex electronic systems. Today semiconductors support computing, communications, transportation, health technologies, industrial control and many other fields. Their performance depends not only on shrinking components but also on material choices, circuit design, manufacturing methods, energy use and reliable access to specialized production capacity.