Inside every electronic device, the flow of electricity is controlled by a switch called a transistor. For decades, these switches were made from silicon. More recently, engineers have turned to a material called gallium nitride (GaN), which enables small, efficient devices like smartphone chargers.
However, at very high voltages, electric fields inside these transistors can concentrate at specific points, causing them to fail prematurely. As a result, today's GaN devices still struggle to perform at the highest voltage levels achieved by silicon.
To overcome this limitation, researchers in the Power and Wide-band-gap Electronics Research Lab ( POWERlab ) in EPFL's School of Engineering have introduced a new class of GaN transistor: the intrinsic polarization superjunction, or iPSJ. The chip-sized device, made from layers of gallium nitride on a low-cost silicon base, can withstand nearly 4 kilovolts (kV) before breaking down, a record for this type of technology. At the same time, it maintains low resistance, helping to reduce energy losses that would otherwise be released as heat.
The combination of high-voltage capability and low resistance is essential for efficient power conversion in AI data centers and renewable energy systems. "We achieve this by exploiting a natural polarization effect that is unique to GaN," explains POWERlab head Elison Matioli. "Our work could enable robust, efficient, high-voltage power electronics at much more compact scales."
Engineering a natural phenomenon
Thanks to gallium nitride's crystal structure, internal electric forces gather mobile electrons into thin sheets that carry current. However, in conventional GaN transistors, these electron sheets are also an Achilles heel: when the device turns off, negatively charged electrons are pushed out of the current pathway, leaving behind positive charge with no matching negative charge. This imbalance concentrates voltage at a single spot in the device, producing an intense electric field that can trigger breakdown.
The POWERlab's new work, published in Nature Electronics, shows how to prevent this charge imbalance. They engineered the transistor's GaN layers so that a second sheet of positive charge forms naturally alongside the electron sheet, creating matched positive and negative charges. By carefully tuning the material thickness, the team ensures that the two charge sheets balance each other throughout the device. As a result, when the device turns off, excess charge does not accumulate, allowing the voltage to spread out evenly along the transistor's length—much like lying down distributes your weight on thin ice—rather than piling up dangerously.
Toward next-generation power electronics
The innovative balanced design allows the POWERlab's transistor to withstand more than five times the voltage of commercial GaN power devices, which break down around 600–650 V. "Our device can hold high voltage across a wide temperature range, making it suitable for EVs or industrial power systems, where electronics must operate reliably under high temperatures and electrical stress," says PhD student and co-first author Luca Mazzone.
PhD student and co-first author Yuan Zong adds that another major advantage of the approach is that it eliminates the need for chemical doping, which is used to control charge in conventional devices. "Doping-based charge balancing in GaN can be highly temperature sensitive. Our doping-free design is key to the robustness of our device."
In complementary work , the POWERlab has shown how adding multiple conduction channels to power-electronics components distributes current to reduce resistance and overheating, like adding more lanes to a highway allows traffic to flow more smoothly and prevent traffic jams. "Our next goal is to combine these two approaches to address the twin challenges facing next-generation power electronics: handling very high voltages safely, while minimizing electrical resistance and the resulting energy loss," Matioli summarizes.
