What is an AC/DC Power Adapter using GaN (gallium nitride)?

This page explains AC/DC Power Adapter and switching power supplies equipped with GaN (gallium nitride) ICs, known as next-generation semiconductors. They are used in USB-PD adapters developed by UNIFIVE.

Next-Generation Semiconductor: GaN-Powered AC/DC Power Adapter

What is GaN?

Recently, USB AC/DC Power Adapters equipped with GaN PD have become increasingly common in electronics retail stores. "GaN" refers to gallium nitride, a next-generation material attracting attention for bringing revolutionary changes to the field of power electronics. For decades, silicon-based MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) have played a key role in converting energy into electricity and have become indispensable in modern daily life. However, improvements in conventional silicon MOSFETs and power efficiency have theoretical limits, and current technology is approaching a level where further improvement is extremely difficult.

In recent years, as demands for higher power density and efficiency have increased, developed countries in particular have introduced various regulations to curb environmental pollution. Under this global trend emphasizing environmental responsibility, silicon faces challenges in meeting these expectations. In contrast, gallium nitride offers characteristics that meet the growing need for greater efficiency, performance, and power density in power systems, and is rapidly spreading as a key next-generation power switching technology to replace silicon.

So, what is gallium nitride?

Gallium nitride does not exist naturally as an element. Gallium is typically obtained as a byproduct when refining aluminum from bauxite ore or processing sphalerite to produce zinc, resulting in very low carbon dioxide emissions during extraction and purification. More than 300 tons of gallium are produced annually, and global reserves are estimated to exceed 1 million tons. Because it is produced as a byproduct, it is relatively inexpensive at about $300 per kilogram, which is 1/200 the price of gold at approximately $60,000 per kilogram.

In addition to its environmental benefits, it is a binary III-V direct transition semiconductor material suitable for high-power transistors that can operate correctly even at high temperatures.

The History of GaN

The melting point of pure gallium is only about 30°C, meaning it can melt in the palm of your hand at body temperature. It took another 65 years before gallium nitride was first synthesized, and single-crystal GaN films could not be grown until the 1960s. The compound GaN has a melting point of over 1,600°C, about 200°C higher than that of silicon.

In 1972, a GaN-based LED doped with magnesium was developed. This was a groundbreaking achievement. Although it was not initially bright enough for commercial use, it was the first LED capable of emitting blue-violet light.

Since the 1990s, gallium nitride has been widely used in light-emitting diodes (LEDs). GaN emits the blue light used in Blu-ray disc readers. It is also used in semiconductor power devices, RF components, lasers, and photonics. In the future, GaN is expected to be used in the field of sensor technology as well.

In 2006, production began on enhancement-mode GaN transistors (also known as GaN FETs), in which GaN thin films were grown on an AlN layer of standard silicon wafers using metal-organic chemical vapor deposition (MOCVD). The AlN layer functions as a buffer between the substrate and GaN. This new method enabled GaN transistors to be manufactured in existing silicon fabrication facilities using nearly the same processes. By utilizing established processes, low-cost production comparable to silicon became possible, reducing barriers to introducing compact, high-performance transistors. More specifically, all semiconductor materials have what is known as a bandgap, which refers to the energy range in a solid where electron states cannot exist. Simply put, the bandgap determines how well a material can conduct electricity. Silicon has a bandgap of 1.12 eV, whereas gallium nitride has a bandgap of 3.4 eV. This wider bandgap means GaN can withstand higher voltages and temperatures than silicon MOSFETs.

Thanks to this wide bandgap, GaN enables applications in high-output, high-frequency optoelectronic devices. Because it can operate at much higher temperatures and voltages than gallium arsenide (GaAs) transistors, it is considered ideal for power amplifiers in microwave and terahertz (THz) devices used in imaging and sensing applications.

Advantages of GaN

What advantages are gained by adopting GaN, a material that enables high-output and high-frequency optoelectronic devices, in AC/DC Power Adapters? Below are the main benefits of using GaN in AC/DC Power Adapters.

GaN is often compared with silicon-based materials, which are currently the standard. Silicon-based MOSFETs are widely used as power switches in applications ranging from a few dozen watts to hundreds or even thousands of watts, including AC/DC power supplies, DC/DC converters, and motor control devices. Packaging, on-resistance (RDS), rated voltage, and switching speed have continuously improved.

However, due to decades of technological advancement, the performance of silicon-based semiconductors is approaching its theoretical limit, leaving little room for further improvement. In contrast, GaN-based power devices are high-electron-mobility transistors with higher critical electric field strength than silicon. This high electron mobility means GaN can handle stronger electric fields than silicon, and under the same on-resistance and breakdown voltage conditions, GaN devices can be made smaller than silicon semiconductors.

GaN FETs feature extremely fast switching speeds and excellent reverse recovery characteristics, which are essential for low-loss and high-efficiency performance. Currently, many 600/650V-rated GaN FETs are available on the market.

The main advantages of using them in AC/DC Power Adapters can be summarized in the following three points:

Reduced Heat Generation

Due to its wide bandgap, GaN has higher thermal conductivity than silicon. This allows GaN-based devices to operate at higher temperatures and enables more efficient cooling, keeping AC adapters cooler and protecting them from heat-related damage.

Higher Power Density and Smaller Size

Because switching frequencies and operating temperatures are higher than those of silicon components, it is possible to reduce the size of heat sinks, eliminate cooling fans, and reduce magnetic components. Higher switching frequencies of GaN components also allow inductors and capacitors used in power circuits to be made smaller. As a result, the number of electronic components inside the AC/DC Power Adapter can be reduced, enabling a more compact housing.

Reduced Acoustic Noise and Wireless Power Transmission

Higher frequencies reduce acoustic noise in motor-driven applications. They also enable higher-output wireless power transmission, increasing spatial flexibility and allowing a wider air gap between transmitter and receiver. This technology is currently being researched for supplying power to electric vehicles.

GaN-Powered AC/DC Power Adapter Developed by UNIFIVE

Related content