Ultra-scaled AlN/GaN enhancement-& depletion-mode nanoribbon HEMTs

Due to its high electron density (> 1× 10
¹³
cm
^-2
) and high electron mobility (> 1000 cm
²
/V.s), AIN/GaN high-electron mobility transistors (HEMTs) present themselves as attractive candidates for high power and high speed applications. In order to continue increasing their high frequency performance, gate length (L
_g
) needs to be scaled downed below 30 nm. For ultrascaled HEMTs, the barrier thickness includes the thickness of Al(GaIn)N and a possible gate dielectric. To maintain the aspect ratio of L
_g
to barrier thickness (t
_g
) with a reasonable two-dimensional electron gas (2DEG) channel and low gate leakage, the gate length will be limited to be ~ 75 nm assuming a 2 nm AlN and a 3 nm gate dielectric. In this paper, a 3-dimensional nano-ribbon AIN/GaN HEMT structure is studied by simulations in comparison with experiments as a candidate for mitigating the short channel effects. By reducing the ribbon width, the device threshold voltage can also be continuously tuned from depletion mode to enhancement mode.