Atul Thakur

Gallium nitride (GaN) is a wide-bandgap semiconductor with a 3.4 eV bandgap, a high critical breakdown field, high electron mobility and high saturation velocity. Those four properties are the physical basis of its high-frequency, high-efficiency behavior, and are the reason GaN is now considered candidate hardware for 6G radio front-ends. GaN high-electron-mobility transistors and monolithic microwave integrated circuits deliver high power at mm-wave and THz frequencies, which are needed for efficient power amplifiers and RF front-ends. Substrate choice sets the practical limits. GaN-on-Si is inexpensive, scalable and compatible with complementary metal-oxide-semiconductor processing; GaN-on-SiC gives the best balance of power, efficiency and reliability at mm-wave; GaN-on-Diamond gives the highest areal power density but is not yet manufacturable in volume. Packaging and thermal management matter as much as the transistor itself. Flip-chip bonding and device-embedded printed circuit board substrates cut parasitic inductance in high-frequency modules, and monolithic integration of power devices with control circuits is the direction of travel for compact GaN integrated circuits. This review follows one chain of reasoning: GaN material properties, then device-level RF metrics, then 6G system requirements. It also sets out what still blocks deployment. The main barriers are efficiency in the THz band, thermal management, heterogeneous integration and the shortage of reliability data under RF stress.