Characterization of hexagonal defects in gallium nitride on sapphire

Hexagonal pits on the surface of GaN grown by an HVPE technique were characterized by SEM, CL-imaging, and micro-Raman scattering techniques. From the CL-imaging, there was seen to be a bright ring around the hexagonal pits, thereby implying disuniformities in the crystal surrounding the hexagonal pits. Then, micro-Raman techniques were employed for detailed analysis both inside and outside the hexagonal pits. E₂² phonons were monitored in order to characterize the strain. The film became more tensile by 0.13 GPa when the laser beam was scanned from the outside of the bright ring shown in the CL-imaging to the center of the hexagonal pit.