What Are Semiconductor Devices?

Semiconductor devices are electronic components fabricated from materials whose electrical conductivity falls between that of conductors and insulators and can be controlled through chemical doping, applied electric fields, or illumination. They form the foundational building blocks of modern electronics, providing functions including signal amplification, switching, rectification, and light emission. Silicon is the dominant semiconductor material because of its abundance, its well-understood oxide interface chemistry, and the mature manufacturing infrastructure built around it, but germanium, gallium arsenide, silicon carbide, and gallium nitride are used in specialized applications requiring properties that silicon cannot provide.

The discipline began in earnest with the invention of the point-contact transistor at Bell Laboratories in 1947 by William Shockley, John Bardeen, and Walter Brattain. That discovery initiated five decades of exponential scaling, described by Gordon Moore's 1965 observation that transistor counts on a chip double roughly every two years, driving MOSFET gate lengths from tens of micrometers to below five nanometers.

MOSFETs and FETs

The metal-oxide-semiconductor field-effect transistor (MOSFET) is the most widely manufactured electronic device in history, serving as the switching element in essentially all digital integrated circuits. In a MOSFET, a voltage applied to the gate terminal controls the conductivity of a channel between source and drain by modulating the charge density in the semiconductor beneath a thin gate dielectric. CMOS (complementary MOS) technology combines n-channel and p-channel MOSFETs to build logic gates that draw current only during switching transitions, enabling the low static power consumption that has made dense integration practical. Field-effect transistors more broadly, including junction FETs (JFETs), high-electron-mobility transistors (HEMTs), and thin-film transistors (TFTs), share the principle of voltage-controlled conductivity through a gate field. The IRDS (International Roadmap for Devices and Systems) published through IEEE tracks the technology nodes and device structures expected to sustain scaling over the coming decade.

BJTs and Analog Mixed-Signal Devices

Bipolar junction transistors (BJTs) are three-terminal devices in which a small base current controls a much larger collector current through minority carrier injection across p-n junctions. BJTs provide higher transconductance than comparable MOSFETs at a given bias current, making them preferred for certain high-frequency amplifier and precision analog circuit applications. Heterojunction bipolar transistors (HBTs), fabricated in III-V compound semiconductors or silicon-germanium, achieve transition frequencies exceeding several hundred gigahertz and are used in RF front-ends for cellular handsets and millimeter-wave communications. Analog mixed-signal devices combine analog amplifiers, voltage references, digital-to-analog converters, and analog-to-digital converters on a single chip, serving as the interface between the continuous physical world and the discrete digital domain in applications from data acquisition systems to wireless transceivers.

Power Semiconductor Devices and IGBTs

Power semiconductor devices are designed to control the flow of electrical energy at voltages and currents far beyond what signal-level devices can handle. The insulated gate bipolar transistor (IGBT) combines the voltage-controlled gate of a MOSFET with the bipolar conduction mechanism that provides low on-state voltage drop at high current densities, making it the dominant switching device in motor drives, inverters for renewable energy systems, and traction systems for electric vehicles and rail. Power MOSFETs are preferred at lower voltages (below approximately 200 V) because of their faster switching speed. Thyristors (SCRs) and gate turn-off thyristors (GTOs) handle the highest power levels in high-voltage direct current (HVDC) transmission. The IEEE Power Electronics Society supports the research and standards community that develops power device technology.

Wide-Bandgap Semiconductors

Wide-bandgap semiconductors, principally silicon carbide (SiC) and gallium nitride (GaN), have bandgap energies of roughly 3.3 eV and 3.4 eV respectively, compared to silicon's 1.1 eV. The wider bandgap translates to higher breakdown field strength, allowing thinner drift regions for a given blocking voltage, lower on-resistance, and operation at junction temperatures up to 200 degrees C or beyond. SiC Schottky diodes and MOSFETs are now mainstream in electric vehicle inverters and solar power converters. GaN transistors dominate in compact, high-frequency power supplies and RF power amplifiers for base stations. Research on wide-bandgap device reliability and packaging is published in IEEE Transactions on Power Electronics.

Applications

Semiconductor devices have applications in a wide range of fields, including:

• Consumer electronics, including smartphones, computers, and televisions
• Power conversion and motor control in industrial drives and electric vehicles
• Wireless communications, from cellular base stations to satellite transponders
• Medical electronics, including implantable devices and diagnostic imaging systems
• Renewable energy systems, in photovoltaic inverters and wind turbine converters
• Defense and aerospace, in radar, electronic warfare, and avionics systems