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.