Gallium arsenide (GaAs) is a compound semiconductor material composed of gallium and arsenic. Unlike silicon, which is a single-element semiconductor, GaAs is a member of the III-V group of materials. This unique structure grants it two primary properties that differentiate it from silicon for specialized applications. Its direct bandgap allows it to convert electrical energy directly into light very efficiently, making it the preferred material for optical devices. Furthermore, its significantly higher electron mobility means electrons move much faster than in silicon. This speed makes GaAs indispensable for devices that operate at extremely high frequencies.
High-Speed Wireless and Microwave Devices
The high electron mobility of gallium arsenide makes it the material of choice for high-frequency electronic circuits, particularly in the microwave and millimeter-wave spectrum. GaAs is widely used to manufacture Monolithic Microwave Integrated Circuits (MMICs), which combine active components like transistors and passive components onto a single chip. These MMICs are essential in wireless communication systems that demand high speed and low noise performance.
A large portion of wireless infrastructure and consumer electronics rely on GaAs-based power amplifiers (PAs). PAs are essential for boosting the radio frequency signal transmitted by devices like cell phones and Wi-Fi routers before it is sent to an antenna. While Gallium Nitride (GaN) is emerging for very high-power applications, GaAs remains dominant in the high-volume, low-to-medium power segment of the consumer market.
Beyond consumer devices, GaAs is crucial for specialized systems requiring effective function at high frequencies. Radar installations and electronic warfare equipment frequently incorporate GaAs components for signal processing and transmission at microwave frequencies, often exceeding 30 gigahertz. The technology is also essential for satellite communication systems (SATCOM), where it maintains signal integrity and high data throughput over vast distances.
Optoelectronic Components
Gallium arsenide’s direct bandgap enables its extensive use in optoelectronics, which involves the interaction between light and electrical energy. Due to this structure, an electron can drop directly from the conduction band to the valence band, releasing a photon in the process. This efficient conversion is difficult to achieve with silicon, which has an indirect bandgap structure.
This capability is exploited in the manufacturing of semiconductor lasers and light-emitting diodes (LEDs). Simple GaAs LEDs emit light in the near-infrared region, making them suitable for applications like remote controls and optical sensors. More complex structures, such as Vertical-Cavity Surface-Emitting Lasers (VCSELs) and edge-emitting lasers, are also built on GaAs substrates.
These lasers are a foundation of modern data transmission, powering the fiber optic communication networks that form the backbone of the internet. A GaAs laser rapidly converts electrical data signals into light pulses, which are then converted back into electrical signals by GaAs-based photodetectors. GaAs lasers are also found in optical storage drives, including CD, DVD, and Blu-ray players, where they precisely read and write data.
Specialized Photovoltaic Applications
While standard terrestrial solar panels use inexpensive silicon, gallium arsenide is employed in specialized, high-performance solar cells where efficiency and durability are paramount. Its direct bandgap allows GaAs to absorb sunlight and convert it into electricity with much higher efficiency than silicon. This performance is maximized in multi-junction solar cells, where layers of GaAs and related compounds are stacked to capture a wider range of the solar spectrum.
These multi-junction cells are the preferred power source for spacecraft, including satellites and Mars rovers, where maximizing energy output per area is critical due to weight and size constraints. The material also resists damage caused by high-energy particle radiation in space, ensuring a longer operational lifespan.
On Earth, GaAs cells are used in Concentrated Photovoltaic (CPV) systems. CPV systems use lenses or mirrors to focus sunlight onto small GaAs cells, sometimes concentrating the light hundreds of times. This technique makes the expensive GaAs material more cost-effective. The high efficiency and superior performance of GaAs solar cells at elevated operating temperatures make them well-suited for these high-concentration, high-heat environments.