Electronics

/ˌɛf iː tiː/

noun — "transistors controlled by electric fields instead of currents."

FET (Field-Effect Transistor) is a type of transistor in which the current flowing between the source and drain terminals is controlled by an electric field applied to the gate terminal. Unlike bipolar junction transistors (BJTs) that rely on carrier injection and base current, FETs modulate conductivity through voltage applied to the gate, providing high input impedance, low power consumption, and excellent signal control. They are widely used in analog and digital circuits, RF amplification, switching applications, and integrated circuits.

Technically, FETs come in several types, including Junction FETs (JFETs), Metal-Oxide-Semiconductor FETs (MOSFETs), and high-performance variants like HEMT. The gate voltage controls the width of a conductive channel between source and drain, which in turn modulates the current. In MOSFETs, an insulated gate allows almost no direct current flow into the control terminal, yielding high input resistance and low leakage. FETs are classified as depletion-mode or enhancement-mode depending on whether the default channel is naturally conductive or requires voltage to turn on.

Key characteristics of FETs include:

• Voltage-controlled: gate voltage regulates current, unlike BJTs which require input current.
• High input impedance: minimally loads preceding circuits.
• Low power consumption: ideal for energy-efficient devices.
• Scalability: fundamental to modern CMOS integrated circuits.
• Variants for speed and frequency: including HEMT for RF and microwave applications.

In practical workflows, FETs are used in switching and amplification roles. In a microcontroller circuit, MOSFETs might switch power to motors or LEDs without significant voltage drop, while in RF applications, JFETs or HEMTs provide low-noise amplification of signals. Designers choose FET type based on frequency, voltage, and power requirements.

Conceptually, a FET acts like a water faucet: the gate voltage is the handle, controlling the flow of electrons (current) through a channel (pipe) between source and drain.

Intuition anchor: FET turns voltage into precise current control, forming the backbone of modern low-power and high-speed electronics.

Related links include HEMT, MOSFET, JFET, and CMOS.

/ˌeɪtʃ iː ɛm tiː/

noun — "transistors that move electrons at lightning speed."

HEMT (High Electron Mobility Transistor) is a field-effect transistor (FET) designed for ultra-high-speed and high-frequency applications by exploiting the high mobility of electrons in a heterojunction interface. Unlike conventional FETs, which rely on doped semiconductors, HEMT devices combine layers of different semiconductor materials—typically a wide bandgap material like GaN or AlGaAs and a narrow bandgap material like GaAs—creating a two-dimensional electron gas (2DEG) at the interface. This 2DEG allows electrons to flow with minimal scattering, dramatically increasing transistor speed and reducing noise.

Technically, HEMT operation relies on the formation of a heterojunction, where the conduction band discontinuity confines electrons in a high-mobility channel. Gate voltage controls the electron density in this channel, modulating current between the source and drain. HEMTs exhibit high transconductance, low gate capacitance, and exceptional high-frequency response, making them ideal for RF amplification, satellite communications, microwave systems, and low-noise amplifiers.

Key characteristics of HEMT include:

• High electron mobility: electrons traverse the channel with minimal scattering.
• High-frequency performance: suitable for GHz and even THz applications.
• Low noise: excellent for sensitive amplification in communication systems.
• High transconductance: small voltage changes at the gate produce large changes in current.
• Material heterostructure: uses layered semiconductors to create the 2DEG.

In practical workflows, HEMTs are deployed in RF front-ends, such as satellite receivers, cellular base stations, radar systems, and millimeter-wave communication links. For example, in a low-noise amplifier for satellite signals, a HEMT boosts faint signals while adding minimal noise, preserving signal integrity for downstream processing. Designers leverage HEMTs’ speed and efficiency to achieve high gain with reduced power consumption.

Conceptually, HEMT behaves like a superhighway for electrons: instead of navigating through rough, crowded streets of conventional semiconductors, electrons flow almost frictionlessly along a dedicated, ultra-smooth channel, reaching their destination faster and cleaner.

Intuition anchor: HEMT transforms material science into velocity, enabling next-generation electronics to operate at the edge of frequency and performance limits.

Related links include GaAs, AlGaAs, GaN, and Low-Noise Amplifier.