Semiconductor device

A semiconductor device is an electronic component that exploits the distinctive electrical properties of semiconductor materials. These properties, found in materials such as silicon, germanium and gallium arsenide, allow conductivity to be precisely controlled by doping, electric and magnetic fields, temperature changes or exposure to light. As a result, semiconductor devices form the foundation of modern electronics, having replaced vacuum tubes almost entirely. They are manufactured either as discrete components or as integrated circuits containing hundreds to billions of interconnected devices fabricated on a single wafer substrate.

Structure and Behaviour

The electrical behaviour of semiconductor devices derives from the movement of charge carriers—electrons and holes—within a crystalline lattice. Doping introduces controlled quantities of impurities to alter carrier concentration. p-type semiconductors contain excess holes created by trivalent dopants such as boron or gallium, while n-type semiconductors contain excess electrons produced by pentavalent dopants such as phosphorus or arsenic.
Current conduction depends on the interplay between these carriers. When p-type and n-type regions are brought together, they form a p–n junction, characterised by a depletion region in which mobile carriers recombine and leave behind fixed ions. This region supports an internal electric field, which determines the direction and magnitude of current flow when an external voltage is applied. Semiconductor devices rely on these controlled junctions to achieve functions such as rectification, amplification and switching. The ability to modify conductivity using external fields or stimuli also enables semiconductors to serve as highly sensitive sensors.
Manufacturing processes carefully regulate dopant concentration and spatial distribution to achieve precise electrical characteristics. To produce predictable device performance, the location of p-type and n-type zones must be controlled at microscopic scales, often with nanometre precision.

Main Types of Semiconductor Devices

Semiconductor devices fall broadly into diodes, transistors and various specialised components.
DiodesA diode is typically constructed from a single p–n junction. Under forward bias, the internal barrier of the junction decreases, enabling a substantial current to flow. Under reverse bias, the depletion region expands and conduction is heavily restricted. Variants of the basic diode include:• Photodiodes, designed to generate charge carriers when exposed to light;• Light-emitting diodes (LEDs) and laser diodes, which produce light when electrons recombine with holes in suitable compound semiconductors.
Bipolar Junction Transistors (BJTs)BJTs comprise two p–n junctions arranged in either npn or pnp formation. They include three terminals: the emitter, base and collector. A small current injected into the base–emitter junction modulates the current through the base–collector junction, allowing the transistor to amplify signals. This property made BJTs central to early solid-state electronics.
Field-Effect Transistors (FETs)FETs operate by controlling carrier flow using an electric field rather than by direct current injection. In a junction FET (JFET), a reverse-biased junction modulates the width of a conducting channel. The more widely used MOSFET (metal–oxide–semiconductor field-effect transistor) employs an insulated gate electrode to induce an inversion layer, forming a conductive path between the source and drain terminals. MOSFETs may be n-channel or p-channel, depending on the carrier type. Their scalability, low power consumption and compatibility with integrated circuit fabrication make them the most prevalent semiconductor devices today. More than sextillions of MOSFETs have been produced since their invention, with billions manufactured each day.
Other Device CategoriesSemiconductor devices come in additional forms:• Two-terminal devices such as rectifiers and LEDs;• Three-terminal devices including insulated-gate bipolar transistors (IGBTs);• Four-terminal devices such as magnetic field sensors and optocouplers.Each device exploits the versatility of semiconductor behaviour to perform functions ranging from sensing to high-power switching.

Materials

Semiconductor device technology relies overwhelmingly on silicon, which offers an optimal balance of availability, mechanical strength, manageable processing techniques and thermal stability. Silicon is grown into large-diameter monocrystalline boules that can be sliced into wafers, enabling high-volume production.
Other materials include:• Germanium, historically important and now commonly alloyed with silicon for high-speed applications;• Gallium arsenide (GaAs), advantageous for high-frequency and optoelectronic devices but costly to produce at large wafer sizes;• Gallium nitride (GaN), valued for its wide band gap and high electron mobility, increasingly used in power electronics and LEDs;• Silicon carbide (SiC), suited to high-temperature, high-voltage and radiation-intensive environments;• Indium compounds, including indium arsenide and indium phosphide, used widely in solid-state lasers and infrared devices;• Organic semiconductors, commonly applied in organic LEDs and flexible electronics.
Each material offers a distinct set of electrical, optical and thermal properties, informing its suitability for particular technological applications.

Applications

Semiconductor devices are fundamental to all modern electronic systems. Digital circuits, which form the basis of microprocessors, memory chips and programmable logic, rely on transistors acting as on–off switches. MOSFETs, in particular, determine logic states according to gate voltage, permitting the creation of logic gates and complex computational architectures.
In analogue circuits, transistors handle continuously varying signals, enabling them to function as amplifiers, oscillators and modulators. Devices that interface between analogue and digital domains, such as analogue-to-digital converters, also use semiconductor components.
Diodes and other optoelectronic devices are indispensable in laser systems, photodetection, solar energy conversion and lighting technologies. High-power semiconductor switches support energy distribution networks, electric vehicles and industrial automation. Sensors based on semiconductors convert physical phenomena—including light, pressure and magnetic fields—into measurable electronic signals.

Manufacturing and Integration

Integrated circuits bring together vast numbers of semiconductor devices on a single slice of silicon or another material. Advances in semiconductor fabrication have enabled the miniaturisation and performance improvements that underpin contemporary computing and communications. The semiconductor industry has experienced sustained growth since the late twentieth century, with annual device production reaching trillions.