Compound Semiconductors: GaAs, GaN, and SiC

Compound semiconductors are crystalline materials composed of two or more elements that exhibit semiconducting properties superior to silicon in specific applications. While silicon dominates mainstream digital logic and memory chips, compound semiconductors have become indispensable in domains where silicon reaches its physical limits: high-frequency radio communications, high-power switching, extreme-temperature operation, and optoelectronic devices. The three most commercially important compound semiconductor materials today are gallium arsenide, gallium nitride, and silicon carbide.

Gallium Arsenide (GaAs)

Gallium arsenide has been the workhorse compound semiconductor for radio frequency (RF) and microwave applications for decades. GaAs offers electron mobility approximately five times higher than silicon, enabling transistors that switch at frequencies well into the gigahertz range with low noise. This makes GaAs the material of choice for power amplifiers in mobile phones, Wi-Fi routers, satellite communications equipment, and 5G infrastructure.

Every smartphone sold today contains multiple GaAs power amplifier chips that boost the radio signal for cellular transmission. The expansion of 5G networks, which operate at higher frequencies and require more RF components per base station, is driving sustained growth in GaAs demand. GaAs is also essential for photovoltaic cells used in space applications, where its superior efficiency (over 30 percent for multi-junction cells) justifies the higher cost compared to silicon solar cells.

The mineral inputs for GaAs are gallium and arsenic. Gallium is a byproduct of aluminum refining from bauxite ore and zinc production, meaning its supply cannot be independently scaled by simply opening new mines. China produces approximately 80 percent of the world's primary gallium, a concentration that became acutely visible when China imposed export licensing requirements on gallium in July 2023. Arsenic, while less supply-constrained, is toxic and subject to strict environmental regulations that limit where processing facilities can operate.

Gallium Nitride (GaN)

Gallium nitride has emerged as one of the most transformative semiconductor materials of the 2020s. GaN's wide bandgap, high breakdown voltage, and excellent electron mobility make it superior to both silicon and GaAs for power conversion applications. GaN transistors can switch power more efficiently, at higher frequencies, and in smaller form factors than silicon alternatives, enabling more compact and efficient power supplies, chargers, and inverters.

The consumer electronics market has been an early adopter of GaN, with fast chargers for laptops and smartphones now routinely using GaN power switches instead of silicon MOSFETs. In the data center industry, GaN-based power supplies reduce energy losses in the power delivery systems that consume a significant fraction of total facility energy. Military applications include radar systems, electronic warfare equipment, and satellite communications, where GaN's ability to handle high power densities at microwave frequencies provides a decisive performance advantage.

GaN devices are fabricated by growing thin gallium nitride crystal layers on substrate wafers, typically silicon, silicon carbide, or sapphire. The gallium requirement is modest on a per-device basis, but total demand is growing rapidly as GaN adoption accelerates across consumer, industrial, automotive, and defense sectors. The same gallium supply concentration that affects GaAs applies equally to GaN, making gallium one of the most strategically sensitive minerals in the semiconductor ecosystem.

Silicon Carbide (SiC)

Silicon carbide has become the power semiconductor material of choice for electric vehicle inverters and high-power industrial applications. SiC's wide bandgap (3.26 eV compared to 1.12 eV for silicon) allows devices to operate at higher voltages, higher temperatures, and higher switching frequencies with significantly lower energy losses. Tesla's adoption of SiC MOSFETs in its Model 3 inverter in 2018 was a watershed moment that accelerated the entire automotive industry's transition to SiC power electronics.

A typical EV inverter using SiC devices is 5 to 10 percent more efficient than a silicon-based equivalent, translating directly into extended driving range from the same battery capacity. This efficiency advantage has made SiC power modules a near-universal choice for premium EVs, and the technology is rapidly moving into mainstream models. Beyond automotive applications, SiC is used in solar inverters, electric rail traction systems, industrial motor drives, and grid infrastructure.

The production of SiC wafers is exceptionally challenging. Silicon carbide crystals are grown using physical vapor transport at temperatures exceeding 2,000 degrees Celsius in a process that can take one to two weeks per boule. The resulting crystal must be sliced, polished, and processed to extremely tight tolerances. Defect density in SiC wafers remains higher than in silicon, and yields are lower, contributing to SiC devices costing several times more than silicon equivalents. Wolfspeed (formerly Cree), STMicroelectronics, Rohm, Infineon, and Onsemi are the leading SiC wafer and device producers. The raw materials, high-purity silicon and carbon, are not themselves supply-constrained, but the specialized manufacturing equipment and process expertise represent significant barriers to entry.

Indium Phosphide (InP) and Other Compound Materials

Beyond the three dominant compound semiconductors, several other materials serve critical niche applications. Indium phosphide (InP) is essential for high-speed fiber-optic communications, operating at the 1,310 nm and 1,550 nm wavelengths used in telecommunications infrastructure. As data traffic grows exponentially, InP-based lasers, detectors, and modulators become increasingly important. Indium, like gallium, is a byproduct metal, produced primarily as a byproduct of zinc refining, and faces its own supply concentration challenges.

Germanium, while technically an elemental semiconductor, is used in combination with silicon for advanced transistor architectures (SiGe) in high-frequency wireless and fiber-optic applications. Germanium also serves as a substrate for multi-junction solar cells in space applications. China produces approximately 60 percent of the world's refined germanium, and it was included alongside gallium in China's 2023 export control measures. The interconnected web of compound semiconductor materials, each dependent on one or more supply-constrained minerals, creates a fragile ecosystem where disruption to any single element can cascade through multiple technology sectors.