What Is Gallium Arsenide?

Gallium arsenide (GaAs) is a III-V compound semiconductor formed from gallium and arsenic, two elements drawn from the third and fifth columns of the periodic table. It crystallizes in the zinc blende structure and possesses a direct bandgap of approximately 1.42 eV at room temperature, a property that distinguishes it sharply from silicon and enables efficient light emission. GaAs has been central to high-frequency electronics, optoelectronics, and photovoltaics since the 1960s, and it remains one of the most studied and widely deployed compound semiconductors in electrical engineering.

The material's commercial importance rests on two physical advantages over silicon. Electron mobility in GaAs is roughly six times higher than in silicon, reaching approximately 8,500 cm²/V·s, which allows devices to switch at higher speeds and operate efficiently at microwave and millimeter-wave frequencies. Its direct bandgap also means that electrons can recombine with holes and emit photons without requiring a phonon to conserve momentum, making GaAs a natural substrate for light-emitting diodes and laser diodes. These properties, along with the material's semi-insulating substrate capability, made it the preferred platform for monolithic microwave integrated circuits (MMICs) throughout the 1980s and 1990s.

Semiconductor Material Properties

GaAs exhibits a bandgap, breakdown voltage, and thermal characteristics that collectively suit it to high-power, high-frequency, and optical applications that silicon struggles to serve. The material's breakdown voltage exceeds that of comparably doped silicon devices, supporting higher operating voltages in power amplifiers. Semi-insulating GaAs substrates, produced by doping with chromium or grown under specific conditions to pin the Fermi level near midgap, minimize parasitic capacitance between adjacent circuit elements. This substrate property is critical in microwave integrated circuits where inter-device coupling degrades gain and phase noise. As documented in GaAs photovoltaic research on IEEE Xplore, the combination of direct bandgap and high optical absorption coefficient also makes GaAs a high-efficiency solar cell material, with single-junction efficiencies exceeding 28 percent under concentrated illumination.

AlGaAs/GaAs Heterojunction Bipolar Transistors

The introduction of aluminum gallium arsenide (AlGaAs) as a wider-bandgap emitter material over a GaAs base gave rise to the AlGaAs/GaAs heterojunction bipolar transistor (HBT), one of the most significant device architectures in RF power electronics. By exploiting the bandgap discontinuity at the AlGaAs/GaAs interface, HBT designers can inject electrons into the base with high efficiency while keeping base resistance low, producing transistors with simultaneous current gain, high power density, and excellent linearity. Studies of AlGaAs/GaAs HBT device and IC technology show that these devices achieve transition frequencies in the 20-40 GHz range with DC current gains of 50 to 100, well-suited to cellular power amplifiers and phased-array radar front ends. The bipolar vertical transport structure of the HBT also offers better wafer-area utilization than field-effect alternatives, contributing to the compact die sizes required in mobile handsets. AlGaAs/GaAs HBTs dominated the power amplifier market for 2G and 3G cellular phones and continue to appear in RF modules where their linearity advantage matters.

Applications

Gallium arsenide has applications in a wide range of fields, including:

• RF and microwave power amplifiers for cellular handsets and base stations
• Phased-array radar front-end modules
• Satellite communications transponders and low-noise amplifiers
• High-efficiency single-junction and multi-junction photovoltaic cells for space and concentrated solar
• Laser diodes and GaAs-based microwave diodes for optical communications and sensing
• Monolithic microwave integrated circuits (MMICs) for defense and commercial wireless systems