Preparation of a freestanding GaN substrate in the Na-flux method by laser-assisted separation

Abstract We have fabricated large-diameter, high-quality gallium nitride (GaN) substrates by the multipoint seed (MPS) technique in the Na-flux method. To obtain crack-free freestanding GaN crystals, in this study we employed laser-assisted separation (LAS) as a new technique to separate GaN from a sapphire substrate. In LAS, the GaN crystal around the GaN-sapphire interface is partially decomposed by irradiating a laser onto the seed substrate before growth. Since this technique reduces the contact area between the sapphire and GaN, separation occurs spontaneously during the cooling process after growth. We found an appropriate LAS processing pattern for separation and successfully obtained freestanding GaN crystal without cracks. By combining LAS with the MPS method, we succeeded in growing crack-free crystals even in film thicknesses in which cracks occur in conventional MPS substrates.