ETCH PIT DEVELOPMENT AND GROWTH ON GAAS(110)

We used scanning tunneling microscopy to study etch pits that are form ed 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 row s wide correspond to pairwise removal of Ga and As from surface lattic e sites. These pits tend to grow along [1(1) over bar0$] and have ends that are equally likely to be bounded by either Ga or As atoms. In ad dition, there is etching across adjacent rows. The resulting pits cros s several zigzag rows and have kinked [1(1) over bar0$] sides and irre gular ends. When these pits grow larger, they increasingly exhibit kin ked (1(1) over bar2$) boundaries and hexagonal appearances. Rebonding of As atoms at pit boundaries to exposed second-layer As atoms was obs erved, and an analysis of the pit boundaries indicates that there are equal numbers of As and Cia terminations. We suggest that etching alon g [1(1) over bar0$] involves removal of a Ga atom that was either a pi t boundary atom or next to a rebonded As boundary atom and that such p rocesses are equally accessible.