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Abstract

The indium-stabilized GaAs(001)-c(8x2) surface was investigated
by surface x-ray diffraction and x-ray standing waves. We find
that the reconstruction closely resembles the c(8x2) structure
described by the recently proposed unified model for clean III-
V semiconductor surfaces [Kumpf , Phys. Rev. Lett. 86, 3586
(2001)]. Consistent with this unified model, no In dimers are
found for the present surface. Instead, for coverages less than
0.25 monolayers, the In adatoms adsorb at the initially
unoccupied hollow sites to form In rows along the [110]
direction. Between the In rows, surface and subsurface Ga
dimers are found to coexist in the trench areas. Above 0.25
monolayers, the additional In adatoms fill the trenches and
replace the surface Ga atoms. The final structure of the
surface layer is essentially identical to the InAs clean
surface, except that the In heights are substantially different
due to the lateral strain induced by the lattice mismatch. This
structural difference explains why the ladder-type pattern
observed previously by scanning tunneling microscopy only
appears for the In/GaAs(001) and InAs/GaAs(001) surfaces, but
not for the InAs clean surface. The structural model we propose
for the In-stabilized GaAs(001)-c(8x2) surface, which fully
agrees with the scanning tunneling microscopy results, should
therefore generally apply to strained InAs(001) surfaces.