  The junctions formed between gate contact and III-nitride are crucial
components of GaN-based electronics and optoelectronics. In this work,
solution-processed inorganic Ti3C2Tx MXene films were spray coated on the
AlGaN/GaN epitaxial wafer as the gate contact. The workfounction of MXene films
was effectively enhanced by partial oxidization process, and accordingly, the
gate leakage current and off-state drain current were significantly suppressed.
The van der Waals heterojunction between MXene films and III-nitride without
direct chemical bonding retained the pristine atomically flat native oxides of
III-nitride, record high Ion/Ioff current ratio of 1013, and near ideal
subthreshold swing of 61 mV/dec was achieved in the Schottky-Type gate GaN
HEMTs. In addition, the MXene gate GaN HEMTs display superior electron mobility
and transcoductance, high uniformity with 20 measured transistors. The
unprecedented performance can be correlated to the damage-free interface
between MXene and III-nitride, negligible atomic diffusion of MXene into the
semiconductor layer, and excellent adhesion between MXene and III-nitride. This
work provides an alternative method to create contact not only in GaN HEMTs but
also in other electronic and optoelectronic devices which uniquely features
cost-effective, non-vacuum, high deposition rate, and damage-free properties.
