Morphology and polytype disturbances in sublimation growth of SiC epitaxial layers

Epitaxial layers of 6H and 4H-SiC have been grown with high growth rate by sublimation epitaxy on SiC substrates with different surface orientation. Polytype disturbances, i.e. regions within the layer where the polytype differs from that of the underlying substrate, may be observed at domain boundaries, defects and along the edges of the samples. The formation of polytype disturbances is more pronounced as the off-axis angle of the substrate decreases. For on-axis substrates, due to a dislocation controlled growth mechanism, many nucleation centers are formed thus creating several domains with polycrystalline growth along the boundaries. This results in a severe roughening of the layer surfaces. With increasing substrate off-orientation, the morphology improves and the appearance of polytype disturbances is diminished or prevented. For thick layers obtained with high growth rates, the surfaces of the layers grown on vicinal substrates are specular with some defects which are formed from obstacles. The growth proceeds via step-flow growth mechanism. A polytype change at the edge, where the growth steps start, may occur indicating a change in the growth mechanism from step-flow growth to 2D nucleation. 3C-SiC can become the dominant polytype in the epitaxial layer grown on 6H- or 4H-SiC substrates. The polytype disturbance at the edge is considerably reduced or has completely disappeared if the layer thickness does not exceed 300-400 mu m as obtained with moderate growth rate of 100-200 mu m/h. (C) 1999 Elsevier Science B.V. All rights reserved.