GaN vs. Silicon in High-Frequency Power Transistors

Introduction

Fig. 1: Frequency versus switching loss for GaN HEMT and Si IGBT. [6] (Image source: Z. Jahan)

Silicon (Si) has long dominated digital logic because its native gate oxide enables precise, reliable transistor control, but these advantages do not extend to high-frequency power electronics where maintaining low switching energy at higher frequencies is essential. [1] Wide bandgap semiconductors such as gallium nitride (GaN) have transformed the field of power electronics by enabling devices to have significantly lower switching losses and higher efficiency than traditional silicon power transistors. [2] The following sections analyze the relevant device physics, quantify key material parameters, and highlight real-world applications that demonstrate GaN's advantages.

Why GaN Cannot Replace Silicon in Microcircuitry

For several decades, silicon has been the backbone of digital logic because it forms a native gate oxide, silicon dioxide (SiO₂), which is a thin insulating layer that allows precise control of transistor behavior. Gate oxides are essential in digital logic because they allow the gate to control channel charge without significant leakage, which are important qualities for reliable digital state switching. [1] GaN does not naturally form stable native oxides, making it unsuitable for fabricating small, densely-packed logic transistors with uniform thresholds and reliable long-term behavior. As a result, silicon continues to dominate CMOS logic, while GaN is predominantly used in power transistors where high frequency operation is crucial. [1,2]

Characteristics of Ideal Power Transistors

Power transistors, such as those used in DC-DC converters, must satisfy several fundamental requirements to achieve optimal performance. Power converters are built from power switches plus passive components like inductors. The switching frequency of the transistors determines the required size and energy storage capacity of these passive components. Specifically, when the switching frequency increases, the required inductance and capacitance values decrease, allowing much smaller passive components. [2] As a result, in order to ensure that the passive components are not too large, modern power devices rely on high-frequency operation.

However, switching a transistor has a power cost associated with the energy required to charge and discharge internal capacitances during each transition. The equation for total switching power is given as follows, where f_sw represents switching frequency and E_sw represents the energy dissipated during each transition [1]:

From the equation, it can be seen that as power converters become smaller by operating at high frequencies, switching losses grow linearly with frequency. But, if switching energy per transition is not sufficiently low, then the device will overheat or become inefficient and unreliable. [1] As a result, the ideal power transistor should be able to operate at high frequencies while maintaining a small switching energy per transition. Materials like GaN are attractive specifically because their device parameters allow for this ideal operation.

GaN Device Parameters

GaN's superiority as a power device is due to several key physical parameters, including its wide bandgap, ability to sustain high electric fields, and high electron mobility. These characteristics allow GaN devices to operate at higher voltages and frequencies with significantly lower energy loss than silicon devices, making GaN the better material for power transistors. [2] Each of these parameters are explained in-depth in the following paragraphs.

The first parameter is bandgap, which is the energy needed to free an electron in a semiconductor. Materials with larger bandgaps are therefore able to withstand higher voltages. From Table 1, it can be seen that GaN is a wide bandgap (WBG) semiconductor material with a bandgap of 3.45 eV compared to silicon's 1.12 eV. [2] GaN's wide bandgap allows it to sustain higher electric fields than Si, which leads to the second parameter: critical electric field strength.

The critical electric field strength of a material is the electric field it can tolerate before avalanche breakdown occurs. During avalanche breakdown, carriers gain enough kinetic energy from the electric field to jump into the conduction band and cause an exponential increase in current, but GaN's large bandgap raises this required energy, resulting in a high critical electric field strength. [3] From Table 1, it can be seen that GaN has roughly ten times the critical electric field strength of silicon, allowing GaN devices to have shorter drift regions, and thus lower device capacitances. [2,3] A central parameter is the output capacitance, C_oss, which stores energy given by

This energy must be dissipated during each switching event. GaN's low output capacitance relative to silicon means that its stored energy, and thus the energy required to charge and discharge the output node, is smaller, allowing faster switching to occur. Additionally, because the switching energy linearly scales with capacitance, lower capacitance directly translates to lower energy loss per switching edge. [4] In other words, GaN is capable of achieving high frequency operation at a low switching energy cost due to its wide bandgap and high critical electric field strength.

A third parameter that makes GaN the ideal material for power transistors is its high mobility. Mobility of a material is a measure of how fast its electrons are able to move. From Table 1, it can be seen that GaN's mobility is about 1.3 times higher than silicon's. [2] This higher mobility allows conduction at lower resistance, R_DS(on), for the same device size, which reduces conduction loss and switching intervals since capacitances can be charged and discharged faster. For reference of this resistance difference, a GaN metal-oxide-semiconductor field-effect transistor (MOSFET) has a R_DS(on) of 0.15 ohms at a drain-source voltage of 400 V, while a Si MOSFET has a R_DS(on) of 0.3 ohms at the same operating voltage. [5]

Overall, GaN's high bandgap energy, large critical electric field, and high electron mobility collectively reduce switching losses and enable more compact, efficient power converters. Several experiments support these results, with Fig. 1 showing the results of one experiment comparing the switching losses of Si insulated-gate bipolar transistors (IGBTs) and GaN high-electron-mobility transistors (HEMTs). In this experiment, the GaN HEMT consistently has lower switching losses than the Si IGBT, especially at higher frequencies, demonstrating the superiority of GaN power transistors. [6]

Practical Applications of GaN Power Transistors

GaN's advantageous device parameters have led to the widespread use of GaN power transistors in a variety of applications. For example, companies like Anker have used GaN FETs to build compact laptop and mobile phone chargers that operate at higher frequencies. Whereas a traditional Si MOSFET-based charger would struggle to provide 50 W of charging power, current GaN- based chargers can provide up to 120 W of charging power. [7] Additionally, GaN power transistors are increasingly being used in AI data center power supply units (PSUs), where high switching frequency and efficiency are crucial to support rising GPU power demands. In Infineon's 3.3-kW and 8- kW PSU designs, GaN devices enable converter switching frequencies up to 500 kHz and achieve power densities near 100 W/in, far above what Si MOSFETs can deliver. [8] As data center electricity consumption accelerates, these efficiency and density improvements make GaN a key technology for scalable, energy-efficient power delivery. GaN-based DC-DC converters are also being used to create mid-voltage electric vehicle (EV) chargers in order to enable faster charging with low losses and compact designs. In 400-900 V EV systems, GaN-based chargers have shown to be 30-50% more energy-efficient than silicon-based ones. [9]

Conclusion

GaN's combination of wide bandgap, high breakdown field, low capacitances, and high mobility gives it lower switching and conduction losses than silicon, enabling efficient high- frequency operation. These advantages have been leveraged in consumer and EV chargers and high-density data center supplies, where GaN devices shrink converter size while improving efficiency. Since silicon remains ideal for logic but is limited in high-frequency power applications, GaN has emerged as a useful material for creating energy-efficient power transistors.

© Zara Jahan. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.

References

[1] T. Li et al., "A Native Oxide High-κ Gate Dielectric For Two-Dimensional Dlectronics," Nat. Electron. 3, 473 (2020).

[2] A. Kumar et al., "Wide Band Gap Devices and Their Application in Power Electronics," Energies 15, 9172 (2022).

[3] O. Slobodyan et al., "Analysis of the Dependence of Critical Electric Field on Semiconductor Bandgap," J. Mater. Res. 37, 849 (2022).

[4] V. Joshi et al., "Impact of Parasitic Elements on the Power Dissipation of Si Superjunction MOSFETs, SiC MOSFETs, and GaN HEMTs," Eng. Res. Express 5, 035077 (2023).

[5] E. O. Prado et al., "An Overview About Si, Superjunction, SiC and GaN Power MOSFET Technologies in Power Electronics Applications," Energies 15, 5244 (2022).

[6] B. Wang et al., "A Comparative Study on the Switching Performance of GaN and Si Power Devices for Bipolar Complementary Modulated Converter Legs," Energies 12, 1146 (2019).

[7] F. Yu et al., "Principle, Structure, and Applications of Gallium Nitride High Electron Mobility Transistors (HEMTs)," IEEE 10281163, 2023 19th Intl. Conf. on Natural Computation, Fuzzy Systems and Knowledge Discovery, 29 Jul 23.

[8] J. Chou, "Scaling AI Data Center Power Delivery with Si, SiC, and GaN," Infineon, June 2025.

[9] R. Ponnambalam and I. Vairavasundaram, "GaN-Based DC-DC Converters for EV Fast Charging: A Review of Wide Bandgap Devices Technology," Results Eng. 28, 107548 (2025).