Realization of GaN PolarMOS Using Selective-Area Regrowth by MBE and Its Breakdown Mechanisms.

GaN PolarMOS is a vertical power transistor incorporating the unique polarization-induced bulk doping scheme in III-nitrides for the body p-n junction. We report the realization of this device, wherein the vertical channel, source contact, and body contact regions are successfully formed using three steps of selective-area epitaxial regrowth, all by molecular beam epitaxy (MBE). The fabricated PolarMOS has an excellent on-current of >500 mA mm−1 and a specific on-resistance of 0.66 mΩ · cm2 . The reverse breakdown mechanisms of the PolarMOS are investigated. First, a pronounced source-drain vertical leakage is identified and attributed to the passivation of the buried p-type body, which is subsequently resolved by the sidewall activation method. With the body leakage eliminated, the breakdown voltage is found to be limited by a highly conductive path along the regrowth sidewall interface using the conductive scanning probe technique, despite the absence of apparent structural defects.