  We report a reversible and hysteretic change in the topography measured with
a scanning tunneling microscope near a single Fe dopant in a GaAs surface when
a small positive bias voltage is applied. First-principles calculations of the
formation energy of a single Fe atom embedded in GaAs as a function of
displacement from the substitutional site support the interpretation of a
reversible lattice displacement of the Fe dopant. Our calculations indicate a
second stable configuration for the Fe dopant within the lattice, characterized
by a displacement along the [111] axis, accompanied by a change in atomic
configuration symmetry about the Fe from four-fold to six-fold symmetry. The
resulting atomic configurations are then used within a tight-binding
calculation to determine the effect of a Fe position shift on the topography.
These results expand the range of demonstrated local configurational changes
induced electronically for dopants, and thus may be of use for sensitive
control of dopant properties and dopant-dopant interactions.
