Scaled InAlN/GaN HEMT on Sapphire With fT/fmax of 190/301 GHz

In this brief, a scaled In
$_{{0}.{17}}$
Al
$_{{0}.{83}}\text{N}$
/GaN high-electron-mobility transistor (HEMT) was fabricated on sapphire substrate with 47-nm
${T}$
-gate length, 300-nm source–drain distance, and selective area regrown
$\text{n}^{+}$
-GaN. The device exhibits cutoff frequencies
${f}_{\text {T}}/{f}_{\text {max}}$
of 190/301 GHz, which gives a record sqrt (
${f}_{\text {T}} \times {f}_{\text {max}}{)}$
= 239 GHz among reported Ga-polar GaN-on-sapphire HEMTs. The device shows a maximum current density, a peak external direct current transconductance, and an
${I}_{\text {on}}/{I}_{\text {off}}$
ratio of 1.45 A/mm, 610 mS/mm, and
$2.9\times 10^{6}$
, respectively. Drain-induced barrier lowering of 75 mV/V is measured at
${I}_{\text {ds}}$
= 1 mA/mm between
${V}_{\text {ds}}$
= 1 V and 5 V. The three-terminal OFF-state breakdown voltage is 14.7 V. The effective electron velocity of the 2-D electron gas (2DEG) under the gate foot is estimated to be
$1.4\times 10^{7}$
cm/s. These characteristics of this Ga-polar millimeter wave (mm-wave) GaN-on-sapphire HEMT are comparable with those state-of-the-art counterparts on SiC substrates.