Step bunching mechanism in chemical vapor deposition of 6H- and 4H-SiC{0001}

Step bunching in chemical vapor deposition of 6H- and 4H-SiC on off-oriented {0001} faces is investigated with cross-sectional transmission electron microscopy. On an off-oriented (0001)Si face, three Si-C bilayer-height steps are the most dominant on 6H-SiC and four bilayer-height steps on 4H-SiC. In contrast, single bilayer-height steps show the highest probability on a <(000(1)over bar)C> face for both 6H- and 4H-SiC epilayers grown with a C/Si ratio of 2.0. The increase of C/Si ratio up to 5.0 induces the formation of multiple-height steps even on a C ace. The bunched step height corresponds to the unit cell or the half unit cell of SiC, The mechanism of step bunching is discussed with consideration of surface formation processes. (C) 1997 American Institute of Physics.