Instability of steps during Ga deposition on Si(1Â 1Â 1)

We demonstrate that deposition of foreign atoms can induce step wandering. Low-energy electron microscopy and atomic force microscopy were used to investigate step shape changes during Ga deposition on Si(1 1 1). Dramatic step wandering occurs during the √3 × √3-to-6.3 × 6.3 transition. Due to the difference in the Si atom density between the √3 × √3 and 6.3 × 6.3 structures, steps advance during the phase transition. Because the 6.3 × 6.3 structure is preferentially formed at the lower side of the steps, more Si atoms are incorporated into the steps from the lower side than from the upper side. This asymmetry causes the step wandering.