Investigations of Performances in RF GaN MIS-HEMTs and T-gate Schottky HEMTs with Leakage Current Analysis Using Emission Microscopy

Traditionally, Schottky HEMT structures are commonly used in Gallium Nitride (GaN) devices, but Metal-Insulator-Semiconductor (MIS)-HEMT structures have gained attention for their ability to decrease gate leakage current. In this work, we produced AIGaN/GaN
$\mathbf{MIS}-{\mathbf{HEMTs}}$
and Schottky HEMTs with a 15-nm in-situ SiN layer. The gate leakage current was effectively suppressed with the assistance of the insulator beneath the gate metal, and the
$\mathbf{MIS}-{\mathbf{HEMTs}}$
exhibit improved RF performances
$\left(\mathbf{f_{ T } / f _{\text {MAX }}}=\mathbf{89.95 / 144.95 GHz} \right)$
compared to Schottky HEMTs
$\left(\mathbf{f_{ T } / f _{ MAX }}=\mathbf{45.75 / 135.3 GHz} \right)$
. However, an unexpected increase in device leakage current was observed during off-state drain breakdown analysis. Through emission microscopy (EMMI), we confirmed the presence of surface leakage between the gate-to-drain region via the in-situ SiN layer, which served as the leakage path and caused high leakage current under high drain voltage bias.