Scanning tunnelling microscopy was used to study the etch pits which formed at 650K following exposure of the (110) surface to Br2 at lower temperatures. Dual bias imaging revealed that 80% of the pits that were one to two rows wide corresponded to the pair-wise removal of Ga and As from surface lattice sites. These pits tended to grow along [1¯10] and had ends that were equally likely to be bounded by Ga or As atoms. There was also etching across adjacent rows. The resultant pits crossed several zig-zag rows, and had kinked [1¯10] sides and irregular ends. When these pits grew larger, they increasingly exhibited kinked <1¯12> boundaries and had an hexagonal appearance. Re-bonding of As atoms, at pit boundaries, to exposed second-layer As atoms was observed and an analysis of the pit boundaries indicated that there were equal numbers of As and Ga terminations. It was suggested that etching along [1¯10] involved the removal of a Ga atom that was either a pit boundary atom or was next to a re-bonded As boundary atom, and that such processes were equally accessible.

B.Y.Han, C.Y.Cha, J.H.Weaver: Physical Review B, 1997, 56[8], 4966-70