ScAlN/GaN High-Electron-Mobility Transistors With 2.4-A/mm Current Density and 0.67-S/mm Transconductance

We report the dc and RF performance of ScAlN/GaN high-electron-mobility transistors (HEMTs). The ScAlN/GaN material was epitaxially grown onto a GaN template on a 4-in 4H-SiC substrate by molecular beam epitaxy. The sheet resistance was measured to be 236 ± 4
$\Omega /\square $
across the wafer by the transfer length measurement. Selective area regrowth of highly doped GaN was implemented to reduce contact resistance (
${R}_{C}$
) as low as 0.1
$\Omega \cdot \textsf {mm}$
. HEMT devices with
$\textsf {2}\times \textsf {150}\,\,\mu \text{m}$
gate width and 140-nm T-gate process show a maximum current density and a transconductance of 2.4 A/mm and 0.67 S/mm, respectively. The extrinsic small-signal gain was measured as a function of drain bias and gate length with extrinsic cutoff frequency and maximum oscillation frequency reported up to 88 and 91 GHz, respectively.