Stepped morphology on 4H and 15R silicon carbide: modelling by a random walk

Abstract

A random walk algorithm for modelling the development of stepped morphology in a diffusion mediated step flow growth is applied to the {0001} surface of 4H (hexagonal) and 15R (rhombic) polytype modifications of silicon carbide grown by vapour phase epitaxy. The algorithm includes variable desorption of adatoms from terraces as well as their variable accommodation at steps. By using this algorithm it is shown that characteristic 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 the [0001] direction. A change between ABC and ACB stacking order implies two kinds of adatom accommodation kinetics (fast and slow) at steps in any of the 〈11̄00〉 directions in the {0001} plane which originate from the different number of dangling bonds at the step edge in ABC and ACB 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 simulation show that 4 and 5 ML step heights as well as step bunching are intrinsic properties of the crystal structure and of its kinetical parameters.