Coalescence Growth of Dislocation-Free GaN Crystals by the Na-Flux Method

We have recently shown that dislocation-free GaN crystals could be grown on a GaN point seed by the Na-flux method. To enlarge the diameter of dislocation-free GaN crystals, we propose here the coalescence of GaN crystals grown from many isolated point seeds. In this study, we found that two GaN crystals grown from two point seeds arranged along the $a$-direction coalesced without generating dislocations at the coalescence boundary, and the $c$-axis misorientation between two crystals around the coalescence boundary gradually diminished as the growth proceeded. These results indicate that coalescence growth may become a key technique for fabricating large-diameter dislocation-free GaN crystals.