High Electron Velocity Submicrometer AlN/GaN MOS-HEMTs on Freestanding GaN Substrates.

AlN/GaN heterostructures with 1700-\cm^2/\V\cdot\s Hall mobility have been grown by molecular beam epitaxy on freestanding GaN substrates. Submicrometer gate-length (LG) metal–oxide–semiconductor (MOS) high-electron-mobility transistors (HEMTs) fabricated from this material show excellent dc and RF performance. LG = \100\ \nm devices exhibited a drain current density of 1.5 A/mm, current gain cutoff frequency fT of 165 GHz, a maximum frequency of oscillation f\max of 171 GHz, and intrinsic average electron velocity ve of \1.5 \times \10^7\ \cm/s. The 40-GHz load-pull measurements of LG = \140\ \nm devices showed 1-W/mm output power, with a 4.6-dB gain and 17% power-added efficiency. GaN substrates provide a way of achieving high mobility, high ve, and high RF performance in AlN/GaN transistors. [ABSTRACT FROM AUTHOR]