Coalescence overgrowth of GaN nano-columns with metalorganic chemical vapor deposition

The authors demonstrate the coalescence overgrowth of GaN nano-columns on a (111) Si substrate with metalorganic chemical vapor deposition to show high-quality optical properties in the overgrown film. Plan-view scanning electron microscopy (SEM) shows coalesced surface morphology, although hexagonal structures are still visible in the images. The cross-section cathodoluminescence (CL) image shows more efficient emission in the overgrowth layer than from the nano-column layer. The plan-view CL image demonstrates that the emitted light is mainly from the hexagonal structures. The photoluminescence measurement result indicates that the emission efficiency of the overgrown layer is even higher than that of an undoped GaN thin film of high quality. The presence of hexagonal structures correlates to surface roughness values in the range of several nanometres.