A systematic study of the regrown interface impurities in unintentionally doped Ga-polar c-plane GaN and methods to reduce the same

Abstract

Vertical gallium nitride (GaN) devices are strong candidates for next generation power electronics. Such vertical devices almost always require epitaxial regrowth of GaN. However, impurities present at the regrowth interfaces result in device degradation such as higher leakage current and lower breakdown voltage limiting its performance. While significant interface impurity concentration has been previously detected in the doped samples as well as in the etched-then-regrown samples, the origin of such interface impurity is still not well-understood. In this work, we perform a detailed characterization of the regrowth interface impurities of unintentionally doped (UID) Ga-polar GaN on c-plane sapphire substrate under various growth interruptions. This process (without any doping and without etch-then-regrowth) allows us to probe the relatively pristine regrown interface and thus better understand the origin of regrowth interface impurity. In the metal organic chemical vapor deposition (MOCVD) grown samples, we uncover a significant presence of silicon (Si) impurity concentration at the regrowth interface of an UID GaN for exposure both in air and in glovebox, with ~88% higher impurity concentration for air exposure. This confirms an inevitable incorporation of Si impurities in the regrowth process originating from air, residual impurities in MOCVD environment and a further adsorption of impurities from the MOCVD chamber. We then demonstrate an ultraviolet (UV) ozone-based cleaning technique to reduce the concentration of Si impurities at the regrown interface. Using an iterative UV-ozone cleaning and wet etching treatment, we realize up to ~61% reduction in the peak Si impurity concentrations therefore paving the way to-wards high performance vertical GaN devices.