Dislocation Clustering and Luminescence Nonuniformity in Bulk GaN and Its Homoepitaxial Film

Cathodoluminescence (CL) spectroscopy and mapping techniques were used to study defect and impurity distributions in free-standing bulk GaN substrates prepared by hydride vapor-phase epitaxy. It was found that, in the bulk GaN substrates investigated, dislocation clusters appearing as dark cores in the CL map were surrounded by bright disk-like regions with higher luminescence efficiency than that of the outside areas. This large-area luminescence nonuniformity disappeared in homoepitaxial GaN grown on top of the GaN substrate. Schottky barrier diodes fabricated on the homo-epilayer exhibited low average reverse leakage current, while dislocation clusters duplicated from the original bulk GaN substrate still limited device yield.