Can advanced semiconductors reduce greenhouse gas emissions sufficiently to play a role in the fight against climate change? The answer is affirmative. Such a transformation is, in fact, proceeding in an orderly manner.

Since around 2001, the compound semiconductor gallium nitride (GaN) has sparked a lighting revolution, which, in some respects, is the fastest technological change in human history. According to a study by the International Energy Agency, within just two decades, the share of GaN-based light-emitting diodes (LEDs) in the global lighting market has grown from zero to over 50%. Research firm Mordor Intelligence recently predicted that, globally, LED lighting will reduce electricity consumption for lighting by 30% to 40% over the next seven years. According to data from the United Nations Environment Programme, lighting accounts for approximately 20% of global electricity consumption and 6% of carbon dioxide emissions.

Each wafer contains hundreds of the most advanced power transistors.

This revolution is far from over. Indeed, it is about to leap to a higher level. The semiconductor technology that has transformed the lighting industry, gallium nitride (GaN), is also part of the power electronics revolution, which is on the cusp of taking off. This is because one of the compound semiconductors—silicon carbide (SiC)—has already begun to replace silicon-based electronic products in the vast and important field of power electronics.

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GaN and SiC devices have better performance and higher efficiency than the silicon components they are replacing. With billions of such devices worldwide, many of which operate for several hours a day, the energy savings will be enormous. Compared to the replacement of incandescent lights and other traditional lighting by GaN LEDs, the rise of GaN and SiC power electronic products will ultimately have a greater positive impact on the Earth's climate.

Wasted power will be reduced in almost all places that need to convert alternating current (AC) to direct current (DC) or convert DC to DC. This conversion occurs in wall chargers for mobile phones or laptops, larger chargers and inverters for powering electric vehicles, and elsewhere. As other silicon strongholds also fall to the new semiconductors, similar savings will be achieved. Wireless base station amplifiers are one of the growing applications where these emerging semiconductors clearly have an advantage. In the effort to slow down climate change, eliminating power consumption waste is a low-hanging fruit, and these semiconductors are the way we harvest it.

This is a new example of a common pattern in the history of technology: two competing innovations achieve results at the same time. How will all of this play out? In which application areas will SiC dominate, and in which will GaN dominate? A serious look at the relative advantages of these two semiconductors can provide us with some reliable clues.

Why Power Conversion Matters in Climate Calculations

Before we delve into the semiconductors themselves, let's first consider why we need them. First of all: power conversion is everywhere. It goes far beyond the small wall chargers that power our smartphones, tablets, laptops, and countless other gadgets.

Power conversion is the process of transforming electricity from a form available to a form required for a product to perform its function. Some energy is always lost in this conversion, and since some of these products operate continuously, a significant amount of energy can be saved. Recall: despite a surge in California's economic output, the state's electricity consumption has remained essentially flat since 1980. One of the most important reasons for the steady demand is the significant improvement in the efficiency of refrigerators and air conditioners during this period. The most important factor in this improvement is the use of variable speed drives based on insulated gate bipolar transistors (IGBTs) and other power electronic devices, which greatly improve efficiency.Gallium Nitride and Silicon Carbide: Their Competitive Fields

In the high-voltage power transistor market, gallium nitride (GaN) devices dominate applications below around 400 volts, while silicon carbide (SiC) now has an advantage in applications of 800 volts and above (the market for above 2000 volts is relatively small). As GaN devices improve, the important battlefield between 400 and 1000V will change. For example, with the launch of 1200V GaN transistors (expected to be launched around 2025), the most important market of electric vehicle inverters will join this battle.

SiC and GaN will greatly reduce emissions. According to an analysis of public data by Transphorm, a GaN device company founded in 2007, by 2041, technology based solely on GaN could reduce greenhouse gas emissions by more than 1 billion tons in the United States and India. The data comes from sources such as the International Energy Agency, Statista, and others. The same analysis indicates that 1,400 terawatt-hours of energy could be saved, which is 10% to 15% of the expected energy consumption of the two countries that year.

Advantages of Wide Bandgap

Like ordinary transistors, power transistors can act as amplifiers or switches. An important example of amplification is a wireless base station, which amplifies signals for transmission to smartphones. Around the world, the semiconductors used to manufacture the transistors in these amplifiers are shifting from silicon technology called Laterally Diffused Metal Oxide Semiconductor (LDMOS) to GaN. The new technology has many advantages, including an increase in energy efficiency of 10% or more, depending on the frequency. On the other hand, in power conversion applications, transistors act as switches rather than amplifiers. The standard technique is called pulse-width modulation. For example, in a common type of motor controller, DC pulses are fed into the coil installed on the motor rotor. These pulses create a magnetic field that interacts with the magnetic field of the motor stator, causing the rotor to rotate. The speed of this rotation is controlled by changing the length of the pulses: the shape of these pulses is a square wave, the longer the pulse is "on" rather than "off", the more speed and torque the motor provides. Power transistors complete the switching.

Pulse-width modulation is also used in switching power supplies, which is one of the most common examples of power conversion. Switching power supplies are the type that supplies power to almost all personal computers, mobile devices, and appliances that operate on direct current. Essentially, the input AC voltage is converted to DC, and then this DC is "chopped" into a high-frequency AC square wave. This chopping is done by power transistors, which generate a square wave by turning on and off the DC. The square wave is applied to the transformer, which changes the amplitude of the wave to produce the required output voltage. To obtain a stable DC output, the voltage from the transformer is rectified and filtered.

The focus here is that the characteristics of power transistors almost entirely determine the circuit's ability to perform pulse-width modulation, and thus also determine the efficiency with which the controller regulates voltage. The ideal power transistor completely blocks the current when it is off, even when the applied voltage is high. This characteristic is called a high breakdown field strength, which indicates how much voltage the semiconductor can withstand. On the other hand, when it is in the conductive state, this ideal transistor has very little resistance to the flow of current. This feature stems from the very high mobility of charge (electrons and holes) within the semiconductor lattice. Consider the breakdown field strength and charge mobility as the yin and yang of power semiconductors.

Compared to the silicon semiconductors they replace, GaN and SiC are closer to this ideal state. First, consider the breakdown field strength. Both GaN and SiC belong to the wide bandgap semiconductors. The bandgap of a semiconductor is defined as the energy required for electrons in the semiconductor lattice to transition from the valence band to the conduction band, measured in electron volts. Electrons in the valence band participate in the bonding of atoms within the lattice, while electrons in the conduction band can move freely within the lattice and conduct electricity.

In semiconductors with a wide bandgap, the bonds between atoms are very strong, so the material can generally withstand relatively high voltages before the bonds break, it is said that the transistor will be damaged. Compared to GaN's 3.40eV, the bandgap of silicon is 1.12 electron volts. For the most common type of SiC, the bandgap is 3.26eV. [See the table below, "Bandgap Menagerie"]

Operating speed and the ability to block high voltage are the two most important characteristics of power transistors. These two qualities are determined by the key physical parameters of the semiconductor material used to manufacture the transistors. Speed depends on the mobility and velocity of charge in the semiconductor, while voltage blocking depends on the material's bandgap and electric breakdown field.Now let's take a look at mobility, which is measured in square centimeters per volt-second (cm²/V·s). The product of mobility and the electric field generates the velocity of electrons, and the higher the velocity, the greater the current carried for a given amount of mobile charge. For silicon, this number is 1,450; for SiC, it is about 950; for GaN, it is approximately 2,000. The exceptionally high value of GaN is the reason why it can be used not only for power conversion applications but also for microwave amplifiers. GaN transistors can amplify signals up to 100 GHz in frequency—far higher than the 3 to 4 GHz typically considered the maximum for silicon LDMOS. For reference, the highest millimeter wave frequency for 5G can reach up to 52.6 GHz. This top 5G band has not yet been widely used, but frequencies up to 75 GHz are being deployed in dish-to-dish communication, and researchers are now using frequencies up to 140 GHz for indoor communication. The demand for bandwidth is insatiable.

These performance data are important, but they are not the only criteria for comparing GaN and SiC for any specific application. Other key factors include the ease of use and cost of the devices and their integrated systems. In summary, these factors explain where and why each of these semiconductors begins to replace silicon—and how their future competition may break free from the dilemma.

SiC leads GaN in today's power conversion field

Cree (now Wolfspeed) launched the first commercially viable SiC transistor that outperforms silicon in 2011. It can block 1,200 volts and has a relatively low resistance of 80 milliohms when conducting current. There are currently three types of SiC transistors on the market. Rohm has a trench MOSFET (metal-oxide-semiconductor field-effect transistor); Infineon Technologies, ON Semiconductor Corp., STMicroelectronics, Wolfspeed, and others have DMOS (double-diffused MOS); and Qorvo has a vertical junction field-effect transistor.

A significant advantage of SiC MOSFETs is their similarity to traditional silicon MOSFETs—even the packaging is the same. SiC MOSFETs operate essentially the same way as regular silicon MOSFETs. They have a source, gate, and drain. When the device is turned on, electrons flow from the heavily doped n-type source through the lightly doped body region and then "exhaust" through the conductive substrate. This similarity means that engineers have a minimal learning curve when transitioning to SiC.

Compared to GaN, SiC has other advantages. SiC MOSFETs are inherently "fail-open" devices, which means that if the control circuit fails for any reason, the transistor will stop conducting current. This is an important feature because it largely eliminates the possibility that a fault could lead to a short circuit and fires or explosions. (However, the price paid for this feature is a lower electron mobility, which increases the resistance when the device is turned on.)

But GaN is gaining new attention

GaN brings its own unique advantages. This semiconductor was first commercialized in the market for light-emitting diodes and semiconductor lasers in 2000. It was the first to reliably emit bright green, blue, purple, and ultraviolet light. But well before the commercial breakthrough in optoelectronics, researchers had demonstrated the potential of GaN in high-power electronics. GaN LEDs quickly became popular because they filled the gap for efficient lighting. But GaN for electronic products had to prove itself superior to existing technologies: specifically, Infineon's silicon CoolMOS transistors for power electronics and silicon LDMOS and gallium arsenide transistors for RF electronics.

GaN's main advantage is its extremely high electron mobility. Current, the flow of charge, is equal to the concentration of charge multiplied by their velocity. Therefore, you can achieve high current due to a high concentration or high velocity or some combination of both. GaN transistors are unusual because most of the current flowing through the device is due to electron velocity rather than charge concentration. This means that, in practice, fewer charges must flow into the device to turn it on or off compared to Si or SiC. This, in turn, reduces the energy required for each switching cycle and helps improve efficiency.

One of the two main types of gallium nitride transistors is called an enhancement-mode device. It uses a gate control circuit operating around 6 volts to control the main switching circuit, which can block 600 volts or higher when the control circuit is off. When the device is on (when the gate applies a 6V voltage), electrons flow from the drain to the source in a flat region called a two-dimensional electron gas. In this area, electrons are highly mobile—a factor that helps achieve very high switching speeds—and are confined beneath a barrier of aluminum gallium nitride. When the device is off, the area under the gate depletes of electrons, disconnecting the circuit beneath the gate and stopping the flow of current.At the same time, the high electron mobility of GaN allows switching speeds to reach 50 volts per nanosecond. This characteristic means that power converters based on GaN transistors can operate efficiently at frequencies in the hundreds of kilohertz, while power converters made of silicon or SiC operate at frequencies of about 100 kilohertz.

Overall, high efficiency and high frequency make power converters based on GaN devices very small and light: high efficiency means smaller heat sinks, and operation at high frequencies means that inductors and capacitors can also be very small.

One disadvantage of GaN semiconductors is that they do not yet have reliable insulating technology. This makes the design of fail-safe devices complicated. In other words, if the control circuit fails, the fault opens.

There are two options to achieve this normally closed characteristic. One method is to equip the transistor with a gate that removes the charge in the channel when no voltage is applied to the gate, and only conducts current when a positive voltage is applied to the gate. These are called enhancement mode devices. For example, they are provided by EPC, GaN Systems, Infineon, Innosience, and Navitas. [See illustration, "Enhancement-mode GaN transistor"]

Another option is called the cascode solution. It uses an independent low-loss silicon field-effect transistor to provide fail-safe functionality for the GaN transistor. Power Integrations, Texas Instruments, and Transphorm have used this cascode solution. [See illustration, "Cascode depletion-mode GaN transistor"]

For safety, when the control circuit of the power transistor fails, it must fail into an open-circuit state with no current flow. This is a challenge for gallium nitride devices because they lack a reliable gate insulating material in both high-voltage blocking and conductive states. A solution called the cascode depletion mode uses a low-voltage signal on a silicon field-effect transistor (FET) to control a much larger voltage on a gallium nitride high-electron-mobility transistor [upper right]. If the control circuit fails, the voltage on the FET gate will drop to zero and stop conducting current. As the FET no longer conducts current, the gallium nitride transistor also stops conducting because there is no longer a closed circuit between the drain and source of the combined device.

Any semiconductor comparison is incomplete without considering cost. A rough rule of thumb is that the smaller the die size, the lower the cost, and the die size is the physical area of the integrated circuit that contains the device.

SiC devices now generally have smaller chips than GaN devices. However, the substrate and manufacturing costs of SiC are higher than those of GaN, and in general, the final device costs for power applications of 5 kilowatts and higher are now comparable. However, future trends may favor GaN. I believe this is based on the relative simplicity of GaN devices, which means that production costs are low enough to overcome the larger die size.

That being said, for GaN to be suitable for many high-power applications that also require high voltage, it must have cost-effective high-performance devices rated at 1,200V. After all, SiC transistors are already available at this voltage. Currently, the closest commercial GaN transistors are rated at 900V. Recently, Transphorm also demonstrated 1,200-V devices manufactured on sapphire substrates, with electrical and thermal performance comparable to SiC devices.

Research firm Omdia's forecast for 1,200-V SiC MOSFETs shows a price of 16 cents per ampere in 2025. I estimate that the price of the first generation of 1,200-V GaN transistors in 2025 will be lower than their SiC counterparts due to the lower cost of GaN substrates. Of course, this is just my opinion; we all know exactly what will change in a few years.GaN vs. SiC Competition

Taking into account these relative strengths and weaknesses, let's consider each application one by one and clarify how things might develop.

Electric Vehicle Inverters and Converters

Tesla adopted SiC for its Model 3's onboard or traction inverter in 2017, marking an early significant victory for the semiconductor. In electric vehicles, the traction inverter converts the battery's direct current (DC) to the motor's alternating current (AC). The inverter also controls the motor's speed by changing the frequency of the AC. According to news reports, Mercedes-Benz and Lucid Motors are now also using SiC in their inverters, and other electric vehicle manufacturers are planning to use SiC in their upcoming models. SiC devices are supplied by Infineon, OnSemi, Rohm, Wolfspeed, and others. The power range of EV traction inverters typically ranges from about 35kW for small EVs to 100kW to around 400kW for large vehicles.

However, it is too early to call this competition for SiC. As I pointed out, to break into this market, GaN suppliers must provide 1,200-V devices. Electric vehicle electrical systems currently operate at only 400-volt voltage, but the Porsche Taycan has an 800-volt system, as do Audi, Hyundai, and Kia electric vehicles. Other automakers are expected to follow suit in the coming years. (The Lucid Air has a 900-V system.) I hope to see the first commercial 1,200-V GaN transistors in 2025. These devices will not only be used in vehicles but also in high-speed public EV chargers.

The higher switching speed that GaN may achieve will be a strong advantage for EV inverters, as these switches use the so-called hard-switching technology. Here, the approach to improving performance is to switch very quickly from on to off to minimize the time the device maintains high voltage and passes through high current.

In addition to inverters, electric vehicles are usually also equipped with onboard chargers, which can charge the vehicle by converting AC to DC, utilizing wall (mains) current. Here, GaN is once again very attractive for the same reasons that make it an ideal choice for inverters.

Power Grid Applications

At least for the next decade, ultra-high voltage power conversion for devices rated at 3kV or higher will remain the domain of SiC. These applications include systems that help stabilize the power grid, convert AC to DC, and convert it back at transmission-level voltages, among other uses.

Mobile Phone, Tablet, and Laptop ChargersStarting from 2019, companies such as GaN Systems, Innosilicon, Navitas, Power Integrations, and Transphorm began selling wall chargers based on gallium nitride (GaN) technology.

The high switching speed of GaN and its generally lower cost have made it the dominant player in the low-power market (25 to 500W), where these factors, along with small size and a robust supply chain, are crucial. These early GaN power converters have switching frequencies up to 300 kHz and efficiencies exceeding 92%. They have set power density records, with figures as high as 30W per cubic inch (1.83W/cm³) — about twice the density of the silicon-based chargers they are replacing.

Automated probe systems apply high voltage to stress test power transistors on wafers. Automated systems can test each of about 500 dies in just a few minutes.

Solar Microinverters

In recent years, solar power has achieved success in both utility-scale and distributed (home) applications. For each installation, an inverter is needed to convert the direct current from solar panels into alternating current to power homes or release energy into the grid. Today, utility-scale photovoltaic inverters are the domain of silicon IGBTs and SiC MOSFETs. However, GaN is set to enter the distributed solar market, particularly.

Traditionally, in these distributed installations, all solar panels have an inverter box. But an increasing number of installers prefer systems where each panel has a separate microinverter, and the alternating current is combined before powering the home or the grid. Such a setup means the system can monitor the operation of each panel to optimize the performance of the entire array.

Microinverters or traditional inverter systems are crucial for modern data centers. Coupled with batteries, they create an uninterrupted power supply to prevent outages. Additionally, all data centers use power factor correction circuits, adjusting the AC waveform of the power to improve efficiency and eliminate characteristics that could damage equipment. For these, GaN offers a low-loss and economical solution that is slowly replacing silicon.

5G and 6G Base Stations

GaN's exceptional speed and high power density will enable it to win and ultimately dominate applications in the microwave field, especially 5G and 6G wireless, as well as commercial and military radar. The main competition here is the silicon LDMOS device array, which is cheaper but has lower performance. In fact, GaN has no real competition above 4GHz frequencies.

For 5G and 6G wireless, the key parameter is bandwidth, as it determines how much information the hardware can effectively transmit. Next-generation 5G systems will have a bandwidth of nearly 1GHz, enabling ultra-fast video and other applications.The microwave communication system using Silicon-on-Insulator (SOI) technology offers a 5G+ solution that utilizes high-frequency silicon devices, where the low output power of each device is overcome by a large array. GaN and silicon will coexist in this field for a period of time. The winner for specific applications will depend on the trade-offs between system architecture, cost, and performance.

Radar

The U.S. military is deploying many ground-based radar systems based on GaN electronic devices. This includes the Ground/Air Task-Oriented Radar (G/ATOR) and the active electronically scanned array (AESA) radar built by Northrup-Grumman for the U.S. Marine Corps. Raytheon's SPY6 radar has been delivered to the U.S. Navy and underwent its first sea trial in December 2022. This system significantly expands the range and sensitivity of shipborne radar.

The battle of wide-bandgap materials has just begun

Today, SiC dominates in EV inverters and is generally used where voltage blocking capability and power handling capability are crucial and the frequency is low. GaN is the preferred technology when high-frequency performance is crucial, such as 5G and 6G base stations, as well as radar and high-frequency power conversion applications, such as wall plug adapters, microinverters, and power supplies.

However, the tug-of-war between GaN and SiC has just begun. Regardless of the competition, application by application, market by market, we can be sure that the Earth's environment will be the winner. As this new cycle of technological renewal and revival moves forward irresistibly, tens of billions of tons of greenhouse gas emissions will be avoided in the coming years.