STEPPED MORPHOLOGY ON 4H AND 15R SILICON-CARBIDE - MODELING BY A RANDOM-WALK

A random walk algorithm for modelling the development of stepped morph ology in a diffusion mediated step flow growth is applied to the {0001 } surface of 4H (hexagonal) and 15R (rhombic) polytype modifications o f silicon carbide grown by vapour phase epitaxy. The algorithm include s variable desorption of adatoms from terraces as well as their variab le accommodation at steps. By using this algorithm it is shown that ch aracteristic step heights of 4 and 5 ML often observed on the surface of 4H and 15R SiC are the result of a specific stacking sequence in th e [0001] direction. A change between ABC and ACE stacking order implie s two kinds of adatom accommodation kinetics (fast and slow) at steps in any of the [1 $($) over bar$$ 100] directions in the {0001} plane w hich originate from the different number of dangling bonds at the step edge in ABC and ACE stacked layers. Therefore during the growth fast steps can take over, occupy positions at the top of the step riser and dominate in controlling the growth rate. The results of the simulatio n show that 4 and 5 ML step heights as well as step bunching are intri nsic properties of the crystal structure and of its kinetical paramete rs.