Demonstration of nonpolar m-plane vertical GaN-on-GaN p-n power diodes grown on free-standing GaN substrates

This work demonstrates the first nonpolar vertical GaN on GaN pn power diodes grown on m-plane free standing substrates by MOCVD. The SEM and HRXRD results showed the good crystal quality of the homoepitaxial nonpolar structure with low defect densities. The CL result confirmed the nonpolar p GaN was of high quality with considerably reduced deep level states. At forward bias, the device showed good rectifying behaviors with a turn-on voltage of 4.0 V, an on-resistance of 2.3 mohmcm2, and a high on off ratio of 1e10. At reverse bias, the current leakage and breakdown were described by the trap assisted space charge limited current conduction mechanism, where I was proportional to V power 4.5. The critical electrical field was calculated to be 2.0 MV per cm without field plates or edge termination, which is the highest value reported on nonpolar power devices. The high performance m-plane p-n diodes can serve as key building blocks to further develop nonpolar GaN power electronics and polarization-engineering-related advanced power device structures for power conversion applications.