Etch pit development and growth on GaAs(110)

We used scanning tunneling microscopy to study etch pits that are formed at 650 K after exposure of GaAs(110) to Br-2 at lower temperature. Dual bias imaging reveals that 80% of the pits that are one to two rows wide correspond to pairwise removal of Ga and As from surface lattice sites. These pits tend to grow along [1(1) over bar0$] and have ends that are equally likely to be bounded by either Ga or As atoms. In addition, there is etching across adjacent rows. The resulting pits cross several zigzag rows and have kinked [1(1) over bar0$] sides and irregular ends. When these pits grow larger, they increasingly exhibit kinked (1(1) over bar2$) boundaries and hexagonal appearances. Rebonding of As atoms at pit boundaries to exposed second-layer As atoms was observed, and an analysis of the pit boundaries indicates that there are equal numbers of As and Cia terminations. We suggest that etching along [1(1) over bar0$] involves removal of a Ga atom that was either a pit boundary atom or next to a rebonded As boundary atom and that such processes are equally accessible.