High-quality coalescence of laterally overgrown GaN stripes on GaN/sapphire seed layers

We have characterized GaN stripes grown by lateral epitaxial overgrowth on large-area (2 in.) $SiO2/GaN/Al2O3$ wafers by low-pressure metalorganic chemical vapor deposition before and after coalescence. Using scanning electron microscopy, x-ray diffraction (XRD), transmission electron microscopy (TEM), and atomic force microscope (AFM), it is shown that by first obtaining “wings” (laterally overgrown material) with low tilt relative to the “seed” (underlying) GaN, very few extended defects are formed when wings from neighboring stripes coalesce. After wings with a tilt of ∼0.1° are coalesced and an additional ∼10 μm of GaN is grown, it is found with XRD that peak splitting due to tilt is no longer detectable. TEM and AFM results show that few dislocations (with a linear density $<4×103 cm−1)$ are formed at coalescence fronts.