Atomic and electronic structures of GaAs (001) surface (original) (raw)

Theory of the (3×2) reconstruction of the GaAs(001) surface

Materials Science and Engineering: B, 1999

We discuss an ab initio density functional theory investigation of a (3 ×2) reconstruction of the Ga-rich GaAs(001) surface. Recent experiments identified this new reconstruction as a stable surface of epitaxially grown GaAs doped with indium or carbon (L. Li, et al., Appl. Phys. A 66 (1998) S501; L. Li, et al., Ultramicroscopy 73 (1998) 229). Using our recently developed real-space pseudopotential density functional code, we investigate this (3 × 2) reconstruction and evaluate stabilization mechanisms for the model proposed by the experimentalists, which does not satisfy the electron counting rule. In order to study the effect of In substitution, we consider the dependence of the surface energies of competing reconstructions on surface strain and relative chemical potentials. The effects of carbon substitution are modeled using a charged (3 ×2) reconstruction. These studies support and clarify the proposed structure and stabilization mechanisms. We provide a simple physical explanation for the behavior of the surface energy of the (3 ×2) reconstruction.

GaAs(001) surface reconstructions: geometries, chemical bonding and optical properties

Applied Surface Science, 2002

We re-examine the GaAs(0 0 1) surface by means of first-principles calculations based on a real-space multigrid method. The cð4 Â 4Þ; ð2 Â 4Þ and ð4 Â 2Þ surface reconstructions minimize the surface energy for anion-rich, stoichiometric and cation-rich surfaces, respectively. Structural models proposed in the literature to explain the Ga-rich GaAs(0 0 1) ð4 Â 6Þ surface are dismissed on energetic grounds. The electronic properties of the novel zð4 Â 2Þ structure are discussed in detail. We calculate the reflectance anisotropy of the energetically most favoured surfaces. A strong influence of the surface geometry on the optical anisotropy is found. #

Geometry and electronic structure of GaAs(001)(2 x 4) reconstructions

Physical review. B, Condensed matter, 1996

Structural and electronic properties of the As-rich GaAs͑001͒͑2ϫ4͒ reconstructions are investigated by means of converged first-principles total-energy calculations. For an As coverage of ⌰ϭ3/4, we find the two-dimer ␤2 phase to be energetically preferred over the three-dimer ␤ phase. As the As chemical potential decreases, the ␣ phase of GaAs͑001͒ represents the ground state of the surface. All geometries are characterized by similar structural elements as As dimers with a length of about 2.5 Å, dimer vacancies, and a nearly planar configuration of the threefold-coordinated second-layer Ga atoms leading to a steepening of the dimer block. Consequently, the resulting electronic properties also have similar features. The surface band structures are dominated by filled As-dimer states and empty Ga dangling bonds close to the bulk valence-and conduction-band edge, respectively. The measured Fermi-level pinning cannot be related to intrinsic surface states. The calculated surface states and ionization energies support the ␤2 structure as the surface geometry for an As coverage of ⌰ϭ3/4. ͓S0163-1829͑96͒04248-8͔

Surface phase diagram of (2×4) and (4×2) reconstructions of GaAs(001)

Physical Review B, 2000

Total-energy calculations for a series of (2ϫ4) and (4ϫ2) reconstructed GaAs͑001͒ surfaces not included in previous theoretical studies are presented. A (2ϫ4) surface model containing single anion dimers in the first and third atomic layers is predicted for a balanced surface stoichiometry. It is more stable than the two-Asdimer ␣ structure assumed previously, due to its lower electrostatic energy. Our results for the (4ϫ2) reconstructed surface confirm the two-Ga-dimer ␤2 structure suggested by Biegelsen and co-workers. Nearly degenerate in energy, however, are mixed Ga-As dimers adsorbed on a Ga-terminated substrate.

A UNION OF THE REAL-SPACE AND RECIPROCAL-SPACE VIEW OF THE GaAs(001) SURFACE

International Journal of Modern Physics B, 2001

A union of the real-space and reciprocal space view of the GaAs(001) surface is presented. An optical transmission temperature measurement system allowed fast and accurate temperature determinations of the GaAs(001) substrate. The atomic features of the Ga A s (001)-(2×4) reconstructed surface are resolved with scanning tunneling microscopy and first principles density functional theory. In addition, the 2D lattice-gas Ising model within the grand canonical ensemble can be applied to this surface to understand the thermodynamics. An algorithm for using electron diffraction on the GaAs(001) surface to determine the substrate temperature and tune the nanoscale surface roughness is presented.

GaAs(001): Surface Structure and Optical Properties

physica status solidi (a), 2001

The optical anisotropy of differently reconstructed GaAs(001) surfaces has been analysed both theoretically and experimentally. The atomic structures and RAS spectra are calculated from first principles for the As-rich c(4 Â 4) and b2(2 Â 4) as well as for the stoichiometric a2(2Â4) and the Ga-rich z(4 Â 2) surface phases. These results are compared with spectra recorded at low temperature (40 K). We find good agreement between the calculated and measured data, in particular for the As-rich surface phases. In marked contrast to earlier calculations we find the peak near the E 1 critical point energy, characteristic of the b2(2 Â 4) surface, to originate from electronic transitions in bulk layers. The experimental data for the Ga-rich (4 Â 2) surface phase are less well reproduced, possibly due to surface defects or structural deviations from the z(4 Â 2) model for the surface geometry.

In-induced (4 × 2) reconstructions of GaAs(001) surfaces

Applied Surface Science, 1998

We present first-principles total-energy calculations on In-terminated GaAs(001)(2 X 4) surfaces. The atomic structures and energetics of two structural models suggested from recent experiments are discussed. We favour a surface structure similar to the GaAs(001)/32(4 X 2) surface, where all Ga dimers are replaced by indium. Its stability, however, is limited to In-and As-rich conditions. The surface electronic structure is characterized by filled In sp2-1ike states energetically close to the bulk valence band edge and empty 7r-bonding and 7r *-antibonding combinations of In p~ orbitals in the upper half of the GaAs bulk band gap.

The GaAs(001)-(2 × 4) Surface: Structure, Chemistry, and Adsorbates

The Journal of Physical Chemistry B, 1997

A series of ab initio simulations, based on density functional theory, of the structure of the clean GaAs-(001)-(2 × 4) surface and of C 2 H 2 , C 2 H 4 , and trimethylgallium (TMGa) adsorbates are described. This surface was selected because of its importance in the growth of GaAs by molecular beam epitaxy. After summarizing briefly the theoretical basis of the computational methods used in the paper, we review critically what is known from experiment and theory about the structure of the clean surface. We argue that there is now strong evidence in favor of the "trench dimer" model for the -phase of the clean surface, while the structures of the R and γ phases are less settled. We then present ab initio simulations of the trench dimer, the three dimer, and the gallium rebonded models of the clean GaAs(001)-(2 × 4) surface and discuss their common structural and bonding features. Ab initio simulations of C 2 H 2 and C 2 H 4 adsorbates at arsenic dimers of the GaAs(001)-(2 × 4) surface are then presented. The changes in the bonding configurations of both the adsorbates and the surface arsenic dimers are explained in terms of changes in the bond orders and local hybridization states. The As dimer bond is broken in the stable chemisorbed states of the molecules. However, an intermediate state, in which the As dimer is still intact, provides a significant barrier to chemisorption in both cases. This barrier, and its absence at the Si(001) surface, stems from the two extra electrons in the As dimer compared with the Si dimer. We then go on to describe the results of 14 ab initio simulations of structures connected with the chemisorption and decomposition of TMGa on the GaAs(001)-(2 × 4) surface. TMGa is commonly used in the growth of GaAs crystals from the vapor phase. The results of these simulations are used to explain a number of experimental observations concerning the surface coverage and the decomposition of TMGa to dimethylgallium and monomethylgallium. Significant technical aspects of the calculations, notably the number of relaxed layers in the slab calculations and the necessity to use gradient-corrected adsorption energies, are stressed. The paper also contains critical comments about ab initio simulations of the GaAs-(001)-(2 × 4) clean surface and about the model based on a "linear combination of structural motifs". Discussion of related experimental results appears throughout the paper.

New Ga-enriched reconstructions on the GaAs(001) surface

JETP Letters, 2009

To prepare structure-ordered GaAs(001) surfaces at low temperatures, GaAs(001) surfaces coated with native oxides were exposed in an atomic hydrogen flow in the temperature range 280-450 ° C. The new Ga-enriched GaAs(001) surfaces with the (4 × 4) and (2 × 4)/c(2 × 8) reconstructions were prepared and studied by the methods of X-ray photoelectron spectroscopy, low-energy electron diffraction, and high-resolution characteristic electron energy loss spectroscopy. For the GaAs(001)-(2 × 4) surface, the structure of the Ga-stabilized surface has been proposed and ab initio computed within the (2 × 4) Ga-trimer unit cell model.