Dynamic on Resistance GAN
# GaN Dynamic On-Resistance
A GaN HEMT's on-resistance measured with a simple DC curve tracer looks excellent — that's the number on the datasheet, and it's genuinely what the device achieves under static conditions. Put the same device into a real switching circuit, and its actual on-resistance right after a high-voltage blocking period can be measurably higher than that DC number, sometimes by a large margin, before gradually relaxing back down over microseconds to milliseconds. That gap between static and just-switched on-resistance is dynamic Ron, also called current collapse, and it's one of the defining reliability and design challenges specific to GaN power devices.
Electron trapping in the GaN buffer layer underneath the conducting channel is the physical mechanism, and it's directly triggered by the high-voltage off-state the device just came from. While a GaN HEMT blocks a high drain voltage in its off state, the strong electric field across the device pushes electrons into trap states within the buffer layer beneath the two-dimensional electron gas that normally carries current. Those trapped electrons create a localized negative charge that partially depletes the channel directly above them — even after the device switches back on and gate voltage says the channel should be fully conducting, the trapped charge is still there, still constricting part of the current path, and on-resistance measures higher than the trap-free DC value until those trapped electrons slowly de-trap and the channel recovers.
Dynamic Ron directly costs real conduction loss in any circuit switching the device at high frequency, which is exactly the application GaN was adopted for in the first place. GaN's whole value proposition in power conversion is enabling much higher switching frequencies than silicon can manage efficiently, letting designers shrink passive components and boost power density — but higher switching frequency means the device spends more of its total conduction time in the just-switched, still-elevated-Ron state rather than fully recovered at the DC value, directly eating into the efficiency gain GaN was supposed to deliver. A device with severe dynamic Ron degradation can lose much of its theoretical efficiency advantage in exactly the high-frequency applications it was chosen for, which is why dynamic Ron characterization under realistic switching conditions, not just a static DC measurement, is now a standard qualification requirement for GaN power devices.
Buffer and epitaxial engineering, not circuit-level fixes, are where the real mitigation happens, since the trapping mechanism itself lives in the material stack. Carbon-doped buffer layers, a common technique for achieving high breakdown voltage in GaN-on-silicon devices, unfortunately also introduce deep trap states that worsen dynamic Ron — a direct material tradeoff between breakdown voltage and current-collapse severity that device designers have to balance rather than optimize independently. Field-plate design, which shapes the electric field distribution across the device specifically to reduce peak field at the trap-prone regions, and buffer-layer composition and doping profile tuning both target the trapping mechanism directly at the epitaxial-growth level, since no amount of downstream circuit design can fully compensate for a device whose own semiconductor material is trapping charge during every switching cycle.
The earlier GaN HEMT material in this session's existing coverage establishes the 2DEG structure and the normally-on gate challenge as GaN's basic device physics. Dynamic on-resistance is what happens to that same 2DEG channel under real operating stress — the reliability and performance gap between a GaN device's best-case datasheet number and what it actually delivers switching at speed in a real power converter.