  Wide and ultra-wide band gap semiconductors can provide excellent performance
due to their high energy band gap, which leads to breakdown electric fields
that are more than an order of magnitude higher than conventional silicon
electronics. In materials where p-type doping is not available, achieving this
high breakdown field in a vertical diode or transistor is very challenging. We
propose and demonstrate the use of dielectric heterojunctions that use extreme
permittivity materials to achieve high breakdown field in a unipolar device. We
demonstrate the integration of a high permittivity material BaTiO3 with n-type
$\beta$-Ga2O3 to enable 5.7 MV/cm average electric field and 7 MV/cm peak
electric field at the device edge, while maintaining forward conduction with
relatively low on-resistance and voltage loss. The proposed dielectric
heterojunction could enable new design strategies to achieve theoretical device
performance limits in wide and ultra-wide band gap semiconductors where bipolar
doping is challenging.
