Growth of bulk GaN crystal by Na flux method

Abstract

With current technologies, dislocation-free bulk shape GaN crystals with centimeter-size can be grown from small seed crystals. This technique can be realized by putting a sapphire plate with a small hole (0.5~1.5 mm in diameter) on a GaN plate seed. Centimeter-sized bulk GaN single crystals with large dislocation-free areas could be fabricated by this technique. Cathodoluminescence measurement at the interface between the seed and the grown crystal has revealed that almost all dislocations propagated from the GaN seed were bent and terminated at the initial growth stage. To enlarge the diameter of bulk shape GaN crystals, we have developed the coalescence of GaN crystals from many isolated small seeds. As a first step, we grew two GaN point seeds and coalesced them. Two GaN point seeds were established by mounting a sapphire plate with two small holes. We have found the two GaN crystals grown from two separate seed area coalesced without generating dislocations at a coalescence boundary. The grown GaN crystal can remove from substrate easily during the growth. This phenomenon is effective to reduce the stress in the grown GaN crystal. 2-inch GaN crystals by the coalescence technique. Some of the crystals have very large curvature radius (~100 m).