Adsorption of atomic oxygen on GaAs(001)-(2x4) and the resulting surface structures

The naturally occurring oxide of GaAs has a high density of defects that pi n the Fermi level at the GaAs surface. The principle electronic defect caus ing the Fermi level pinning is widely believed to be an arsenic antisite do uble donor. We have used scanning tunneling microscopy to show that the ars enic antisite defects are formed during the initial period of oxidation of GaAs(001) by atomic oxygen. Atomic oxygen displaces a single arsenic atom i n the top layer leaving behind an undimerized arsenic atom with a half-fill ed dangling bond. The displaced arsenic atoms bond to remaining arsenic dim ers to form arsenic antisites. Cluster calculations confirm the assignment of the oxygen binding sites and the role of undimerized single arsenic atom s as acceptor sites. (C) 2001 American Institute of Physics.