InAlN/AlN/GaN HEMTs With Regrown Ohmic Contacts and $f_{T}$ of 370 GHz

We report 30-nm-gate-length InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs) with a record current gain cutoff frequency
$(f_{T})$
of 370 GHz. The HEMT without back barrier exhibits an extrinsic transconductance
$(g_{\rm m.ext})$
of 650 mS/mm and an on/off current ratio of
$10^{6}$
owing to the incorporation of dielectric-free passivation and regrown ohmic contacts with a contact resistance of 0.16
$\Omega\cdot\hbox{mm}$
. Delay analysis suggests that the high
$f_{T}$
is a result of low gate–drain parasitics associated with the rectangular gate. Although it appears possible to reach 500-GHz
$f_{T}$
by further reducing the gate length, it is imperative to investigate alternative structures that offer higher mobility/velocity while keeping the best possible electrostatic control in ultrascaled geometry.