What Is Gallium Nitride?

Gallium nitride (GaN) is a wide-bandgap compound semiconductor formed from gallium and nitrogen, with a bandgap of approximately 3.4 eV, more than three times that of silicon. It crystallizes primarily in the wurtzite structure and exhibits a combination of high electron mobility, high breakdown electric field, and good thermal stability that silicon cannot match in the same device geometry. GaN emerged in the 1990s as the foundation for blue and ultraviolet LEDs and later for high-power, high-frequency transistors. It now sits at the center of two major technology shifts: the move to wide-bandgap power electronics and the deployment of solid-state RF amplifiers in 5G infrastructure and radar systems.

The material's electronic properties derive directly from its crystal structure and polarization characteristics. At the GaN heterojunction interface, spontaneous and piezoelectric polarization fields induce a high-density two-dimensional electron gas (2DEG) without intentional doping, a physical effect that underpins the high-electron-mobility transistor (HEMT) architecture.

Material Properties and Crystal Structure

GaN's wurtzite crystal structure produces strong internal polarization fields at heterointerfaces, particularly when grown on aluminum nitride (AlN) or aluminum gallium nitride (AlGaN) layers. The breakdown electric field of GaN is roughly 3.3 MV/cm, about ten times that of silicon, which allows devices to be physically smaller while sustaining the same operating voltage. This combination of high breakdown field and fast electron saturation velocity enables power devices that switch at frequencies of hundreds of kilohertz to several megahertz with on-resistance far below equivalent silicon devices at the same voltage rating. As reviewed in gallium nitride power device research on IEEE Xplore, GaN-on-silicon substrates are now mature enough for volume power electronics manufacturing, which has brought device costs down substantially since 2015.

High-Electron-Mobility Transistors

The dominant GaN device architecture for both power and RF applications is the HEMT, in which an AlGaN layer grown on a GaN buffer generates a 2DEG at the interface with sheet carrier densities exceeding 10¹³ cm⁻². Because the electrons in the 2DEG are confined but not scattered by dopant atoms, they move at high velocity with low resistance, yielding transistors that can operate efficiently at frequencies from audio to millimeter-wave. For power electronics, enhancement-mode (normally-off) GaN HEMTs have replaced silicon MOSFETs in compact chargers, data center power supplies, and inverters where smaller size and higher switching frequency reduce the mass of passive components. NASA's body of knowledge for GaN power electronics reliability documents qualification requirements for these devices in aerospace power systems.

RF and High-Frequency Electronics

GaN HEMTs have become the preferred active device for solid-state RF power amplifiers in frequency bands from L-band through millimeter-wave. Their high power density, typically 4 to 10 W/mm of gate width, exceeds gallium arsenide devices by a factor of five to ten, enabling compact, high-power transmitter modules for 5G base stations, military radar, and electronic warfare systems. The physical reasons for this advantage are the large bandgap and resulting high breakdown voltage, which permit operation at drain voltages of 28 to 50 V where GaAs amplifiers would fail. IEEE Spectrum's coverage of gallium nitride for power-hungry electronics details how these properties translate into system-level gains in base station power efficiency.

Applications

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

• High-power solid-state RF amplifiers for 5G base stations and millimeter-wave communications
• Phased-array radar transmitters for defense and weather sensing
• Compact USB power adapters and data center power supplies
• Motor drives and inverters in electric vehicles and industrial automation
• Blue and ultraviolet LEDs for solid-state lighting and sterilization
• Satellite and space power conversion systems