  The wide bandgap, high-breakdown electric field, and high carrier mobility
makes GaN an ideal material for high-power and high-frequency electronics
applications such as wireless communication and radar systems. However, the
performance and reliability of GaN-based HEMTs are limited by the high channel
temperature induced by Joule-heating in the device channel. High thermal
conductivity substrates integrated with GaN can improve the extraction of heat
from GaN based HEMTs and lower the device operating temperature. However,
heterogeneous integration of GaN with diamond substrates is not trivial and
presents technical challenges to maximize the heat dissipation potential
brought by the diamond substrate. In this work, two modified room temperature
surface activated bonding techniques are used to bond GaN and single crystal
diamond with different interlayer thicknesses. TDTR is used to measure the
thermal properties from room temperature to 480 K. A relatively large TBC of
the GaN-diamond interfaces with a 4nm interlayer was observed and material
characterization was performed to link the structure of the interface to the
TBC. Device modeling shows that the measured GaN-diamond TBC values obtained
from bonding can enable high power GaN devices by taking the full advantage of
the high thermal conductivity of single crystal diamond and achieve excellent
cooling effect. Furthermore, the room-temperature bonding process in this work
do not induce stress problem due to different coefficient of thermal expansion
in other high temperature integration processes in previous studies. Our work
sheds light on the potential for room-temperature heterogeneous integration of
semiconductors with diamond for applications of electronics cooling especially
for GaN-on-diamond devices.
