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Atomic and electronic structures for a number of GaAs(001) surface geometries were studied within the density functional theory (DFT) in order to re-examine the energy stability of surface reconstructions in the Ga-rich limit. The (2 × 4) mixed-dimer model developed for InP(001)-(2 × 4) surface was adopted for Ga-rich GaAs(001)-(2 × 4) surface. It is shown that the energetically favored Ga-rich (2 × 4) reconstructions are stabilized by dimerized Ga and As atoms. Our DFT calculations predict the coexistence of (2 × 4) and (4 × 4) reconstructions on GaAs(001) in the Ga-rich limit.

Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence.-- et al., The surface electronic structure of the narrow-gap seminconductor BiTeI exhibits a large Rashba-splitting which strongly depends on the surface termination. Here we report on a detailed investigation of the surface morphology and electronic properties of cleaved BiTeI single crystals by scanning tunneling microscopy, photoelectron spectroscopy (ARPES, XPS), electron diffraction (SPA-LEED) and density functional theory calculations. Our measurements confirm a previously reported coexistence of Te- and I-terminated surface areas originating from bulk stacking faults and find a characteristic length scale of ∼100 nm for these areas. We show that the two terminations exhibit distinct types of atomic defects in the surface and subsurface layers. For electronic states resided on the I terminations we observe an energy shift depending on the time after cleavage. This aging effect is successfully mimicked by depositon of Cs adatoms found to accumulate on top of the I terminations. As shown theoretically on a microscopic scale, this preferential adsorbing behaviour results from considerably different energetics and surface diffusion lengths at the two terminations. Our investigations provide insight into the importance of structural imperfections as well as intrinsic and extrinsic defects on the electronic properties of BiTeI surfaces and their temporal stability., This work was financially supported by the Deutsche Forschungsgemeinschaft through FOR1162 and the Bundesministerium für Bildung und Forschung (grant numbers 05K10WW1/2 and 05KS1WMB/1). TVK and VIG acknowledge partial support from the Government of Sverdlovsk Region and Russian Foundation for Basic Research (grant no. 13-02-96046_Ural) and the Ural Branch of the Russian Academy of Sciences (grant no. 12-U-2-1002). This publication was funded by the Deutsche Forschungsgemeinschaft and the University of Würzburg in the funding programme Open Access Publishing.

The sequence of surface reconstructions on GaAs(001), usually observed under As desorption in the temperature range from 450 to 580 °C, was obtained by atomic hydrogen (AH) reaction with the oxide-covered GaAs(001) surfaces in the temperature range from 420 to 280 °C. With the decrease in annealing temperature under AH treatment of oxide-covered GaAs(001) surfaces, the recon- structions changed from As-rich (2 × 4)/c(2 × 8) at 420 °C through the intermediate (2 × 6)/(3 × 6) at 380 °C, Ga- stabilized (4 × 2)/c(8 × 2) at 350 °C and (4 × 6) at 330 °C, to a very Ga-rich (4 × 4) at 280 °C, in the order of Ga/As ratio increase. The observed backward reconstructions on the GaAs(001) surface are explained by AH-induced Ga accumulation on the surface and by surfactant activities of AH allowing low-temperature ordering. The Ga-rich (4 × 4) surface structure covered by ΘGa ≈ 0.8 ML was reconstructed to a new Ga-terminated structure with the symmetry of As-rich (2 × 4)/c(2 × 8) surface under vacuum annealing at the temperature higher than 560 °C. DFT calculations support the existence of the energetically favored Ga-rich (2 × 4) reconstruction described by the mixed-dimer model, developed for InP(001)-(2 × 4) surface, and predict the coexistence of (2 × 4) and (4 × 4) reconstructions on GaAs(001) at the Ga-rich limit.