  Owing to the large breakdown electric field, wide bandgap semiconductors such
as SiC, GaN, Ga2O3 and diamond based power devices are the focus for next
generation power switching applications. The unipolar trade-off relationship
between the area specific-on resistance and breakdown voltage is often employed
to compare the performance limitation among various materials. The GaN material
system has a unique advantage due to its prominent spontaneous and
piezoelectric polarization effects in GaN, AlN, InN, AlxInyGaN alloys and
flexibility in inserting appropriate heterojunctions thus dramatically broaden
the device design space.
