Leakage mechanism in ion implantation isolated AlGaN/GaN heterostructures

We report a comprehensive analysis of the leakage current mechanism in ion implantation isolation (I/I/I) regions of GaN high electron mobility transistors. We applied a three-step high-energy low-dose N I/I/I to AlGaN/AlN/GaN heterostructures. High-quality isolation is achieved with isolation sheet resistances Rsh in the range of 1013–1015 Ω/sq. The analysis of isolated heterostructures with varied AlGaN or AlN thicknesses indicates common electron leakage paths at the surface of GaN. The electrostatics of the leakage path is determined by an interplay between the high densities of defects created by I/I/I, the net sheet polarization charges between III-nitrides, and the AlGaN surface states. We find that the activation energy of Rsh positively correlates with the energy level of the leakage path. The energy band diagram of the isolation region is constructed by correlating the activation energies of Rsh with the heteerostructure electrostatics. Moreover, our study makes a novel method to estimate the net active defect density caused by I/I/I: net active defect densities of ∼2 × 1019 and ∼2 × 1018 cm−3 are extracted in the GaN and AlGaN layers, respectively.