This paper reviews how high‑electron‑mobility transistors (HEMTs) made from III‑nitride materials behave at high temperatures. The authors focus mainly on gallium nitride (GaN) devices and on how heat changes their materials, transistor designs, and circuit performance. They identify which parts of the device help it survive heat and which parts are most likely to fail. They also point out a clear gap: very few devices have been shown to run for long periods at temperatures above about 400–500 °C.

HEMTs use a thin conducting sheet called a two‑dimensional electron gas, or 2DEG, that forms where two different semiconductor layers meet. That 2DEG gives high current and low leakage even at high temperature because it does not depend on dopants that break down with heat. The review examines different device styles, including normally‑on (depletion‑mode) devices and normally‑off (enhancement‑mode) designs, and several approaches to make normally‑off transistors, such as adding a p‑GaN gate layer, etching a recessed gate, implanting fluorine to add fixed negative charge, or putting an insulator under the gate (MISHEMT).

The authors summarize how specific materials and layer choices affect thermal stability. Common barrier layers include aluminum‑gallium nitride (AlxGa1−xN), indium‑aluminum nitride (InxAl1−xN), scandium‑aluminum nitride (ScxAl1−xN), and aluminum nitride (AlN). AlGaN is widely used but shows thermal instability above roughly 400 °C, with faster loss of drain current and higher resistance from strain relaxation and dislocations. InAlN can be grown to match GaN and so avoids some strain‑related failures, while ScAlN can give very strong polarization but can suffer decomposition or mismatch at higher Sc content. The review also notes practical design limits, such as keeping Al0.25Ga0.75N below about 30 nm to preserve strain during growth.