Mn-Induced Surface Reconstructions on GaAs(001)

We have systematically studied the
surface reconstructions induced
by the adsoprtion of Mn atoms on GaAs(001). Several types of adsorption
structures were observed depending on the preparation conditions,
and were identified using complementary experimental techniques of
reflection high-energy electron diffraction, scanning tunneling microscopy,
reflectance difference spectroscopy, and X-ray photoelectron spectroscopy.
The sequence of surface structures as a function of As coverage was
confirmed by the experiments and first-principles calculations. Under
the most Ga-rich conditions, (2 × 2)­α and (6 × 2)
structures are formed, both having As atoms at faulted sites and Ga–Ga
dimers at the third atomic layer. As the As coverage is increased,
the structure with Ga–As dimer [(2 × 2)­β] becomes
more stable, and, finally, the c(4 × 4) structure
consisting of three As–As dimers is energetically favored at
the As-rich limit. We found that the location of Mn atoms critically
depends on the surface As coverage: As-deficient (2 × 2)­α,
(6 × 2), and (2 × 2)­β structures have the Mn atoms
at 4-fold hollow sites, while the incorporation of Mn atoms into the
substitutional Ga sites is enhanced in the most As-rich c(4 × 4) structure, in which the upper limit of substitutional
Mn is 0.25 ML.