Cathodoluminescence study of nonuniformity in hydride vapor phase epitaxy-grown thick GaN films

The nonuniformity in hydride vapor phase epitaxy (HVPE)-grown thick GaN was studied using cathodoluminescence (CL) technique. It was found that the nonuniform luminescence feature originated from pit-type defects. Two kinds of pit-type defects were distinguished by their morphology: one was hexagonal V-pit surrounded by 10-11 facets and the other was U-pit with 10-11 facets and the blunt bottom. The 10-11 facets of both pits with N-polarity show the strong CL emission due to the oxygen incorporation, while the matrix with Ga-polarity appeared dark in the CL image. The dim CL contrast was observed in the blunt bottom with the mixed polarities. The blunt bottom suggests the filling of pits during the growth, which may be the key to eliminate pit-type defects in free-standing GaN wafer.