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 introd uction of stacking faults along the [11(2) over bar] step edges. Simil ar results are also observed for Cl- and I-terminated Si(111) surfaces . This strong preference for a particular step edge structure determin es the surface morphology of steps, islands, and etch pits, and has pr ofound ramifications for dry etching and chemical vapor deposition gro wth for this system.