GaN HEMT Knowledge Base
← Hermes pages home

Fundamentals: what a GaN HEMT is

The device stack, material advantages, and the engineering knobs that determine performance.

Last updated: 2026-05-11 · static LLM wiki

Core definition

Layer-stack picture

SourceGateDrain AlGaN barrier GaN channel Buffer / substrate AlGaN/GaN interface 2DEG electron sheet +++ positive polarization sheet charge gate controls channel density

Canonical lateral AlGaN/GaN HEMT: the 2DEG sits on the GaN side of the AlGaN/GaN interface; the gate modulates the channel through the barrier.

A GaN HEMT is a field-effect transistor built around a heterojunction, usually AlGaN/GaN, where electrons conduct in a thin sheet at the interface. The channel is called a 2DEG because carriers are confined vertically but free to move laterally from source to drain.

Unlike a silicon MOSFET, the channel is not primarily created by inversion under an oxide. In the canonical GaN HEMT, it is created by polarization charge at the heterointerface.

Typical lateral AlGaN/GaN stack

  • Substrate: Si for cost and large wafers, SiC for RF thermal performance, sapphire for some legacy/low-cost uses, bulk GaN or AlN for advanced research.
  • Transition/buffer layers: manage lattice/thermal mismatch and isolate the high-voltage device from the substrate.
  • GaN channel: hosts the 2DEG on the GaN side of the interface.
  • AlGaN barrier: supplies band offset, strain, and polarization discontinuity.
  • Optional AlN spacer/back barrier: improves confinement or reduces alloy scattering.
  • Gate: Schottky, MIS, p-GaN, recessed MIS, or cascode-controlled depending on application.
  • Field plates/passivation: shape electric field and reduce trapping/current collapse.

Why GaN beats silicon in the right regime

GaN’s wide bandgap and high critical field allow a shorter, thinner drift region for a given voltage. Its high electron saturation velocity and low gate charge enable fast switching and RF operation. Those material advantages translate into high power density and high-frequency operation — but only if packaging, thermal paths, and reliability are engineered correctly.

GaN is not automatically better everywhere. It shines at compact, high-frequency conversion and RF power. SiC usually dominates at higher voltage and rugged high-power modules; silicon remains cheaper and simpler for many low-stress designs.