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

In this brief, a scaled In<inline-formula> <tex-math notation="LaTeX">$_{{0}.{17}}$ </tex-math></inline-formula>Al<inline-formula> <tex-math notation="LaTeX">$_{{0}.{83}}\text{N}$ </tex-math></inline-formula>/GaN high-electron-mobility transistor (HEMT) was fabricated on sapphire substrate with 47-nm <inline-formula> <tex-math notation="LaTeX">${T}$ </tex-math></inline-formula>-gate length, 300-nm source–drain distance, and selective area regrown <inline-formula> <tex-math notation="LaTeX">$\text{n}^{+}$ </tex-math></inline-formula>-GaN. The device exhibits cutoff frequencies <inline-formula> <tex-math notation="LaTeX">${f}_{\text {T}}/{f}_{\text {max}}$ </tex-math></inline-formula> of 190/301 GHz, which gives a record sqrt (<inline-formula> <tex-math notation="LaTeX">${f}_{\text {T}} \times {f}_{\text {max}}{)}$ </tex-math></inline-formula> = 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 <inline-formula> <tex-math notation="LaTeX">${I}_{\text {on}}/{I}_{\text {off}}$ </tex-math></inline-formula> ratio of 1.45 A/mm, 610 mS/mm, and <inline-formula> <tex-math notation="LaTeX">$2.9\times 10^{6}$ </tex-math></inline-formula>, respectively. Drain-induced barrier lowering of 75 mV/V is measured at <inline-formula> <tex-math notation="LaTeX">${I}_{\text {ds}}$ </tex-math></inline-formula> = 1 mA/mm between <inline-formula> <tex-math notation="LaTeX">${V}_{\text {ds}}$ </tex-math></inline-formula> = 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 <inline-formula> <tex-math notation="LaTeX">$1.4\times 10^{7}$ </tex-math></inline-formula> 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.