Formation of periodic steps with a unit-cell height on 6H–SiC (0001) surface by HCl etching

Step bunching on 6H–SiC (0001)-vicinal face etched by HCl at 1300–1500 °C is investigated by atomic force microscopy. When the substrate has the inclination toward near 〈011̄0〉 or even 〈112̄0〉, continuous parallel and periodic microsteps with six-bilayer height are laid perpendicular to the off direction, although those perpendicular to 〈112̄0〉 are apt to decompose into three bilayer or less. Formation mechanism of unit-cell-height steps is discussed based on consideration of bond configuration at step edges.