Origin of leakage current in vertical GaN devices with nonplanar regrown p-GaN

Abstract

This work demonstrates large-area vertical GaN-on-GaN Schottky barrier diodes (SBDs) with different p-GaN terminations fabricated by the p-GaN regrowth on planar and nonplanar n-GaN structures and studies the leakage current in these regrown p-GaN terminations. The SBDs with planar p-GaN terminations demonstrate a higher breakdown voltage than the non-terminated SBDs. In contrast, the SBDs with nonplanar regrown terminations exhibit a significantly higher leakage current, which agrees with the tunneling behavior. The microscopic current mapping and local current-voltage (I-V) spectra are acquired using conductive atomic force microscopy (C-AFM) in the nonplanar regrown junction region. The local leakage currents and conduction types are derived from the I-V characteristics of the Schottky barrier between the metalized C-AFM tip and GaN. The dominant leakage path is revealed to be the tunneling across the Schottky barrier to the regrowth sidewall assisted by high-concentration interfacial impurities, followed by current flow along the regrowth sidewall. An ∼0.7 μm-wide n-type compensation layer is found next to the non-polar regrowth sidewall, which does not directly induce a major leakage path but moves the p-GaN away from the regrowth interface, thus weakening the p-GaN depletion of the sidewall interfacial impurities as well as facilitating the formation of a crowded electric field and tunneling at the Schottky contact to the regrowth region.