Silicon carbide (SiC) is a promising wide-bandgap semiconductor for applications such as high-power devices, high-voltage switches, high-temperature electronics and microwave components. The prospect of using this material is a large driving force for improving the material growth which is still quite immature in comparison with established semiconductor materials (e.g. silicon). There is an increasing number of reports in growth of large area boules and epilayers, but the fundamental growth issues are often not discussed (or not known) which holds back the advancement in the growth technology.

Chemical vapor deposition (CVD) is the technique which has achieved epitaxial layers with low residual doping (<10¹⁵cm^-3) and smooth surface morphology, two requirements for device quality material. The drawback of CVD is the low growth rate (<5 μm/hr). Since material cost is one limitation for industrial applications, increased growth rates would be preferred.

Two epitaxial techniques which yield high growth rates (several tens or hundreds of μm/hr) are liquid phase epitaxy and sublimation epitaxy, both of which have been investigated within the present work. The first method is appealing since growth from the liquid phase is a growth technique under near equilibrium conditions thus providing a base for growth of high-quality material. In paper I a SiC liquid phase epitaxy technique is described. The growth process and the quality of the grown material are investigated to gain understanding of this high growth rate technique. Several factors affect the quality of the grown material. One important parameter is the quality of the interface at the growing crystal surface. This is studied in paper II for liquid phase growth where the SiC/solvent interfacial properties are investigated. The results are used for estimating the surface free energy of 4H-SiC. In liquid phase epitaxy the influence of gravity induced convection is more pronounced than in vapor phase growth. This effect was studied in paper III where comparisons in growth rate, doping incorporation and structural quality of layers grown on-ground and for the first time for SiC layers grown under microgravity conditions were made.

In liquid phase epitaxy with high growth rates, a smooth surface morphology is difficult to achieve due to increased step heights (up to 1 μm) caused by pronounced stepbunching. For further understanding of SiC epitaxial growth with high growth rates, the sublimation epitaxy growth technique was studied in paper IV. It is shown that growth rates up to 2 mm/hr are achieved and the surface is smooth without observation of macrosteps using optical microscopy. The limitations in growth conditions for morphological stable growth are investigated for 6H and 4H-SiC. Studies of the kinetics show that the growth rate limiting process is sublimation of the SiC source material.

Defects are often observed on as-grown surfaces but for deeper understanding of the formation mechanisms involved, cross-sections of epitaxial layers are important to study. Application of cross-sectional cleavages for investigating SiC epitaxial layers has been investigated in paper V. The preferred cleavage planes are related to the crystal structure of SiC. Appearance of defects and other polytypes than given by the substrate is a difficult matter in the growth process. Fundamentals in formation of these imperfections have been investigated in paper VI for growth using on-axis and offoriented substrates. These issues are more crucial in bulk growth where improper growth behaviour may lead to morphologically unstable growth and a phase transition from 4H-SiC polytype to 6H-SiC during the first millimeters of growth. The initial stages of crystal formation in seeded sublimation bulk growth are studied in paper VII and single 4H-SiC boules without polytype conversion were grown.

The structural quality of the grown material is a fundamental property in growth. In paper VIII structural improvement, as compared with the substrates used, is demonstrated for sublimation epitaxy. Different misoriented domains in the substrate merge into one with one major orientation. A mechanism for this process is proposed. The as-grown surfaces are free of morphological defects which typically appear in SiC epitaxy. It is also shown that the improvement in structural quality is maintained when growth is performed on substrates containing a layer grown by liquid phase epitaxy. This is a technique for reducing micropipe densities in the substrates. Even though starting from a LPE layer surface showing steps, smooth surfaces were achieved using sublimation epitaxy. This finding may have an important practical impact.