In-situ and ex-situ characterizations of PVT-grown 4H-SiC single crystals

4H silicon carbide (4H-SiC) is one of the most promising candidates in high-power and high-frequency devices, owing to its excellent properties such as wide bandgap, high electron mobility, high electric breakdown field and high thermal conductivity. The physical-vapor-transport (PVT) approach has been broadly adopted to grow 4H-SiC single-crystal boules. Because of the high-temperature growth of 4H-SiC single-crystal boules, the PVT system is a 'black-box' system, which decreases the yield and thus increases the cost of 4H-SiC single-crystals. Although advanced modern characterization tools, e.g. atomic force microscopy, x-ray topography, x-ray diffraction and Raman scattering spectroscopy, can provide deep insight into the structural and defect properties of 4H-SiC boules, it is rather limited to gain in-situ information of the growth process by these ex-situ methods. Therefore, the in-situ visualization on the evolution of structural morphologies and defects conducted by x-ray computed tomography (xCT) is of great importance for further development. In this topical review, the application of the xCT technology on the in-situ visualization of the evolution of the growth front, growth rate, defects, and the mass transport of the source material of 4H-SiC are reviewed. The ex-situ characterization of 4H-SiC single-crystal boules are also briefly introduced. This topical review provides insight into the growth process, structural morphology, and defect evolution of PVT-grown 4H-SiC single-crystal boules.