TCAD-Based Analysis on the Impact of AlN Interlayer in Normally-off AlGaN_GaN MISHEMTs with Buried p-Region

With the growing demand for more efficient power conversion and silicon reaching
its theoretical limit, wide bandgap semiconductor devices are emerging as a potential
solution. For instance, Gallium Nitride (GaN)-based high-electron-mobility transistors
(HEMTs) are getting more attention, and several structures for the normally off operation
have been proposed. Adding an AlN interlayer in conventional AlGaN/GaN normally on
HEMT structures is known to enhance the current density. In this work, the effect of an
AlN interlayer in the normally off AlGaN/GaN MISHEMT with a buried p-region was
investigated using a TCAD simulation from Silvaco. The added AlN interlayer increases
the two-dimensional electron gas density, requiring a higher p-doping concentration to
achieve the same threshold voltage. The simulation results show that the overall effect
is a reduction in the device’s current density and peak transconductance by 21.83% and
44.4%, respectively. Further analysis of the current profile shows that because of the buried
p-region and at high gate voltages, the current flows near the AlGaN/GaN interface and
along the insulator/AlGaN interface. Adding an AlN interface blocks the migration of
channel electrons to the insulator/AlGaN interface, resulting in a lower current density.