  In this article, we investigate through numerical simulation the reduction of
self-heating effects (SHEs) in GaN HEMT via the integration of hexagonal boron
nitride (h-BN) as a passivation layer and as a release layer to transfer GaN
HEMT to diamond substrate. The obtained devices exhibit improved thermal
performance compared to SiO2/GaN/sapphire HEMT. The lattice temperature was
reduced from 507 K in SiO2/GaN/sapphire to 372 K in h-BN/GaN/diamond HEMT. The
temperature decrease enhances the drain current and transconductance to 900
mA/mm and 250 mS/mm, corresponding to a 47 % improvement. In addition, the
total thermal resistance Rth is reduced by a factor of 5 from 27 K.mm/W in
GaN/sapphire HEMT to 5.5 K.mm/W in GaN/diamond HEMT. This study indicates that
h-BN integration in GaN HEMT as a top heat spreader and a release layer for
transfer to diamond substrate can be a promising solution to reduce
self-heating effects and extend the device lifetime and reliability.
