245-GHz InAlN/GaN HEMTs With Oxygen Plasma Treatment

We report lattice-matched In
_0.17
Al
_0.83
N/GaN high-electron mobility transistors on a SiC substrate with a record current gain cutoff frequency (
fT
). The key to this performance is the use of an oxygen plasma treatment to form a thin oxide layer on the InAlN barrier and to reduce the gate leakage current by more than two orders of magnitude. In addition, the RF transconductance (
g
_m
) collapse is reduced in the O
₂
-treated devices, which results in a significant improvement in the
f
_T
. In a transistor with a gate length of 30 nm, an
f
_T
of 245 GHz is achieved, the highest value ever reported in GaN-based field-effect transistors.