Effects of morphology during coalescence of GaN crystals on dislocation behavior in the Na-flux point seed technique
Ryotaro Sasaki, Masayuki Imanishi, Shogo Washida, Kosuke Murakami, Shigeyoshi Usami, Mihoko Maruyama, Masashi Yoshimura, Yusuke Mori
Abstract
Abstract We fabricated large-diameter, low-threading dislocation density (TDD) GaN wafers using Na-flux multi-point seed and flux-film-coated (FFC) techniques. In the FFC technique, the crystal grows repeatedly inside and outside the melt to planarize the crystal surface. However, regions where the three pyramidal crystals coalesced at regular intervals exhibited a high TDD exceeding 10 5 cm −2 . Recently, we found that the growth morphology of crystals can be controlled by varying the ratio of the growth time inside and outside the melt using the FFC technique. In this study, we discovered that the TDD above the coalescence region was reduced from 4.4 × 10 5 to 2.5 × 10 5 cm −2 by optimizing growth morphology, such as { <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>10</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mo>̅</mml:mo> </mml:mover> <mml:mn>2</mml:mn> </mml:math> } facet growth and increasing the c -plane sector boundary angle. Furthermore, based on the relationship between the dislocation propagation angle and c -plane sector boundary angle, we propose a growth model for effective TDD reduction.