A synchrotron X-ray topography study of crystallographic defects in ScAlMgO4 single crystals

Abstract

ScAlMgO4 is a promising material that can be used to fabricate lattice-matched substrates for the epitaxial growth of GaN and InGaN. To improve its crystal quality, we used synchrotron X-ray topography to study the dislocations in a 50.8-mm-diameter ScAlMgO4 single crystal grown via the Czochralski method. Dislocation character was analyzed in terms of Burgers vectors by comparing dislocation contrasts recorded using six g-vectors that represented the m+c, a+c, and c-type crystal planes. The central area of the substrate, which corresponded to the portion grown vertically under the seed crystal, was characterized by millimeter-sized domains bound by mixed-type dislocation arrays with both in-plane and c-axis Burgers vectors. Basal plane dislocations (BPDs) typically formed an arrow-like shape with three branches. Growth striations with alternating high- and low-dislocation-density areas were observed in the diameter-expanding area and high-dislocation-density areas were covered with tangled BPD networks. The mechanisms of dislocation generation, multiplication, and reaction are discussed based on their line directions and dislocation character.