Equivalent step structures along inequivalent crystallographic directions on halogen-terminated Si(111)-(1x1) surfaces

Steps in inequivalent crystallographic directions are usually assumed to have different atomic structures. However, this Letter demonstrates that bilayer steps in the two principal crystallographic directions ([<(11)over bar> 2] and [11(2) over bar]) of the Br-terminated Si(111)-(1 x 1) surface have the same atomic edge structure, due to the introduction of stacking faults along the [11(2) over bar] step edges. Similar results are also observed for Cl- and I-terminated Si(111) surfaces. This strong preference for a particular step edge structure determines the surface morphology of steps, islands, and etch pits, and has profound ramifications for dry etching and chemical vapor deposition growth for this system.