Kinetic and electronic properties of surface steps on 4H-SiC epitaxial layers

Step-flow growth is critical to stabilizing the 4H polymorph, reducing defect density, and preserving a smooth surface during the homoepitaxy of 4H silicon carbide (4H-SiC). In this work, the step kinetics and formation mechanism of step bunching during the fast epitaxy of ultra-thick 4H-SiC layers are established. We systematically investigate the effect of growth rate and C/Si ratio on the surface morphologies, step heights, and terrace widths of 4H-SiC homoepitaxial layers. It turns out that increasing the growth rate narrows the process window of a smooth 4H-SiC epi layer surface, as a result of increased adatom flux and supersaturation ratio. When the C/Si ratio increases, both the step height and terrace width increase, resulting in the step bunching and the formation of giant steps higher than 5 nm. On the contrary, when the C/Si ratio decreases from the ideal process window, the decrease in repulsive force between neighboring steps gives rise to the formation of meandering steps that are evenly distributed on the surface of 4H-SiC. Our growth model reveals that the velocity ratio governs step dynamics: optimal ratios maintain smooth growth, while deviations cause either step bunching formation (low ratios) or surface disorder (high ratios), as evidenced by roughness trends. Additionally, we investigate the influence of steps on the crystalline and electronic properties of the 4H-SiC. The results demonstrate that neither step bunching nor giant steps introduce any local strain, lattice disorder, or mid-gap electronic states.