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. P olytype disturbances, i.e. regions within the layer where the polytype diff ers from that of the underlying substrate, may be observed at domain bounda ries, defects and along the edges of the samples. The formation of polytype disturbances is more pronounced as the off-axis angle of the substrate dec reases. For on-axis substrates, due to a dislocation controlled growth mech anism, many nucleation centers are formed thus creating several domains wit h polycrystalline growth along the boundaries. This results in a severe rou ghening of the layer surfaces. With increasing substrate off-orientation, t he morphology improves and the appearance of polytype disturbances is dimin ished or prevented. For thick layers obtained with high growth rates, the s urfaces of the layers grown on vicinal substrates are specular with some de fects which are formed from obstacles. The growth proceeds via step-flow gr owth mechanism. A polytype change at the edge, where the growth steps start , may occur indicating a change in the growth mechanism from step-flow grow th to 2D nucleation. 3C-SiC can become the dominant polytype in the epitaxi al layer grown on 6H- or 4H-SiC substrates. The polytype disturbance at the edge is considerably reduced or has completely disappeared if the layer th ickness 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.