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.