High-Performance AlN/GaN HEMTs on Sapphire Substrate With an Oxidized Gate Insulator

This letter presents transistor device results on ultrathin AlN/GaN high-electron mobility transistors grown on a sapphire substrate with high dc/RF performance, including low gate leakage and high transconductance. Devices with 80- and 180-nm T-gates are compared, which demonstrate drain-induced off -state gate leakage currents below
$\hbox{10}^{-6}\ \hbox{A/mm}$
and extrinsic transconductance
$g_{m} \sim \hbox{500}\ \hbox{mS/mm}$
by utilizing a
$\sim$
2–3 nm amorphous oxide layer formed under the T-gate during processing. In addition, excellent dc results such as
$R_{C} < \hbox{0.50}\ \Omega \cdot \hbox{mm}$
and pulsed
$I_{DS, \max} \sim \hbox{1.75}\ \hbox{A/mm}$
are reported. Small-signal RF performance using an 80-nm T-gate achieved
$f_{t} > \hbox{100} \ \hbox{GHz}$
operation, which is among the best so far reported for AlN/GaN technology.