Research & Development Is gallium nitride (GaN) the silicon of the future?

A power struggle is underway in the world of electronics. Faster, more efficient gallium nitride semiconductors have already usurped traditional silicon MOSFETs in a variety of applications. But is GaN really ready to take the throne?

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What’s gallium nitride (GaN)?

Gallium nitride is a direct bandgap semiconductor material used to manufacture semiconductor devices such as transistors and diodes. This high-performance compound first hit the power electronics market in the 1990s as a vital component in light emitting diodes (LEDs). GaN has a particularly wide bandgap of 3.2 eV, making it capable of handling very high voltages and operating at high temperatures.

It can be used for a wide range of applications—from optoelectronic devices to high-frequency radio communications—and new uses are constantly being found for this efficient, highly powerful semiconductor material.

Current GaN applications include:

• Lasers and photonics applications such as light-emitting diodes (LEDs)

• Solar cells for photovoltaic systems

• Radiation-hardened transistors for satellites

• Radio frequency components such as RF power amplifiers

• Wireless power transmission, e.g. wireless chargers for phones, laptops, game console controllers, heart pumps and other medical applications

• DC-DC converters for datacom applications, e.g. server farms and centralized telecommunications centers

• LiDar (light detection and ranging), e.g. devices in autonomous cars that meas-ure distances using lasers

• Imaging and sensing, e.g. power amplifiers for microwave and terahertz (ThZ) devices

GaN vs. silicon

Before GaN took off, silicon had long been the most widely used material for manufacturing semiconductors. The invention of the silicon MOSFET (metal-oxide-silicon fieldeffect transistor) revolutionized computing and paved the way for the digital age. Now, after decades of dominance, it appears that silicon may have peaked. According to gallium nitride experts GaN Systems, “we are reaching the theoretical limit on how much silicon MOSFETs can be improved, how power-efficient they can be”.

A look at the properties and capabilities of the two semiconductors does suggest that the high-performance newcomer will eventually supersede silicon. When comparing GaN and silicon, the bandgap is a good place to start. GaN’s bandgap is 3.4 eV, whereas silicon has a value of just 1.12 eV. This means GaN semiconductors can sustain higher voltages and survive higher temperatures than silicon MOSFETs. The current can travel faster through GaN semiconductors, ensuring greater efficiency and fewer switching losses when they are used in hardswitching applications. They have less capacitance than silicon MOSFETs, which means that less power is lost when devices are charged and discharged. GaN semiconductors also take up less space on circuit boards, making it possible to manufacture ever-smaller electronic appliances.

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Cost is another key factor. It is possible to grow gallium nitride crystals on top of silicon, so they can be produced in existing silicon manufacturing facilities and do not require costly specialized production sites. Although gallium nitride crystals are currently still more expensive to produce than silicon, GaN semiconductors lower a system’s overall production costs by reducing the size and cost of other components.

GaN semiconductors’ superior speed and efficiency also make them better suited to meeting the environmental pollution regulations that are required to mitigate climate change.

Is there anything GaN can’t do?

As far as semiconductor devices go, GaN appears to tick all the boxes. Yet despite its widespread use in a variety of industries, there are still several applications that it has yet to master.

While GaN semiconductor devices have become indispensable for optoelectronic and high-frequency applications, for example, GaN transistors are not yet as versatile as silicon MOSFETs. The problem lies in the fact that most GaN transistors are depletion-mode or “normally-on” transistors. According to Power Electronics magazine, “deple-tion-mode transistors are inconvenient because at start-up of a power converter, a negative bias must first be applied to the power devices or a short circuit will result”. There is also the fact that electronic circuitry typically requires both depletion-mode and enhancement-mode transistors. However, workarounds for this issue have already been developed and it is surely only a matter of time before GaN semiconductors will appear in even more products and industries.

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