Evidence of the Precipitates in the V-Shaped Defects of Undoped GaN

Precipitates in undoped GaN epilayers with specular surfaces grown on sapphire substrates were imaged by super high-resolution electron microscopy (HREM) and analyzed by energy-dispersive x-ray spectrometry (EDXS). The HREM images of the precipitates appeared more or less hexagonal intersection with several ten-nanometer large, which is the same as that of the V-shape defects. The EDXS spectra of the precipitates were mainly composed of the characteristic x-rays of oxygen, carbon, and gallium elements. The results suggest that the precipitates nucleate at the pinholes of the V-shape cavities and grow as the GaN growth.