High-crystalline-quality AlN grown on SiC substrates by controlling growth mode

•AlN growth on SiC under various supersaturation conditions was investigated.•Cracks in AlN was generated by relaxation of compressive strain during growth.•Compressive strain relaxation in AlN was suppressed by lowering dislocation density.•High-crystalline quality AlN grown on SiC was obtained by multi-step AlN growth. We investigate the relation between growth mode and crystalline quality of AlN directly grown on an on-axis 6H-SiC(0001) substrate under various supersaturation conditions by metal-organic chemical vapor deposition. Although 500-nm-thick AlN fabricated by a two-dimensional (2D) growth mode had smooth surfaces, high threading dislocation density (TDD) and cracks were observed. In contrast, a three-dimensional (3D) growth mode produced spiral growth and crack-free AlN with low TDD. We analyze behaviors of surface morphology, TDD, and strain relaxation of AlN by the change in growth mode, revealing that TDD is correlated with crack generation due to relaxation of compressive strain during AlN growth. To obtain atomically flat AlN on 6H-SiC(0001) to suppress crack generation by the decreased TDD, we performed multi-step 3D and 2D AlN growth. We describe successful fabrication of 600-nm-thick AlN with no crack generation, low TDD, and a 500-nm-wide terrace on an on-axis 6H-SiC(0001) substrate.