Theoretical Study of the Surface Optical Properties of Clean and Hydrogenated GaAs(110) (original) (raw)
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Ab initio calculation of the reflectance anisotropy of GaAs(110)
Physical Review B, 1998
We compute the optical properties of the ͑110͒ surface of gallium arsenide within the first-principles density-functional theory local-density approximation scheme, using norm-conserving pseudopotentials. Starting from the surface electronic structure calculation, we analyze the imaginary part of the theoretical dielectric function, separating surface and bulk contributions. The effects of the nonlocality of the pseudopotential are studied, by working both in the transverse gauge ͑neglecting them͒ and in the longitudinal gauge ͑where they are automatically included͒. The two calculations, although giving different dielectric functions, yield the same reflectance anisotropy, which compares well with experimental data and with previous theoretical results.
Valence band states of H:GaAs(110)
Surface Science, 1994
The two-dimensional surface electronic band structure of H: GaAs(ll0) is studied by angular resolved ultraviolet photoemission spectroscopy along the X'-M and X-M symmetry lines and in the high symmetry points of the surface Brillouin zone. Three surface state bands are resolved in the first 5 eV below the upper valence band edge. A comparison with theoretical band structure calculations yields a satisfactory agreement, giving evidence of hydrogen induced GaAs(ll0) surface derelaxation. The clean GaAs(ll0) surface electronic band structure is studied comparing results with available theoretical and experimental data.
GaAs(110) surface electronic structure by metastable deexcitation spectroscopy
Physical Review B, 1995
Metastable deexcitation spectroscopy was applied to study the surface valence electronic structure of clean cleaved GaAs(110). Metastable deexcitation spectroscopy was flanked by angle-resolved photoemission. An effective surface density of states was derived from the experimental spectrum through deconvolution. Two groups of states were observed in the 0 -4 and 5 -8 eV range of binding energy, respectively. These features were ascribed to emission from surface states. A plane-by-plane tight-binding density-of-states calculation was performed. More quantitative insights were obtained by comparing experimental and theoretical results. The most prominent feature of the first group of states of deconvolution was assigned to surface state As. Contributions from states A4, A3 A1, and A2 were also observed. The doublet of the second group of features was identified with Cq and C1. Relative amplitudes of effective surface density of states were related to surface charge density.
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.
Optical anisotropy spectra of GaAs(001) surfaces
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1992
We present theoretical studies of the optical anisotropy spectra of GaAs(OOl) surfaces with different reconstructions at growth temperatures. The Ga-rich (4 X 2) missing~dimer surface, three different phases (a, (3, and y) of the As-rich (2X4) surface, and an As-rich c(4X4) surface are considered. Total energy calculations within a nearest-neighbor tight-binding model are performed to determine the surface geometry for each reconstruction considered. The difference between reflectance spectra with [110] and [110] polarization for these surfaces is analyzed and compared to available data.
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. #
Reflectance Anisotropy of GaAs(100): Theory and Experiment
Physical Review Letters, 1998
The reflectance anisotropy has been calculated by microscopic tight-binding theory for various configurations of the As-rich GaAs(100) c͑4 3 4͒ and ͑2 3 4͒ reconstructions, based on precise atomic coordinates from ab initio total-energy minimization. The comparison to experimental reflectance anisotropy in combination with scanning tunneling microscopy and low energy electron diffraction allows one to identify precise correlations between structural units and optical features. Clear indications are obtained for the intermediate steps in the surface reconstruction transformation. [S0031-9007(98)06681-2]
Reflectance-difference spectroscopy of (001) GaAs surfaces in ultrahigh vacuum
Physical Review B, 1992
Reflectance-difference spectroscopy (RDS) is employed to study in situ the (4X2), (1X6), (4X6), (3X1), (2X4)-a, (2X4)-P, (2X4)-y, c(4X4), and d(4X4) reconstructions of (001) GaAs surfaces prepared in ultrahigh vacuum (UHV) by molecular-beam epitaxy and simultaneously characterized by reflection high-energy electron diffraction (RHEED). Reproducibility of the data is excellent. %'ith the aid of previous theoretical calculations, we interpret characteristic spectral features at 1.9, 2.6, and 4.2 eV in terms of electronic excitations involving surface dimers of Ga, As, and As, respectively. Because RD couples to local electronic structure rather than to long-range order, RD spectra not only determine surface reconstructions but also provide details not accessible by RHEED, such as the existence of As dimers in the (1 X 6), (4X6), and (3 X 1}reconstructions and of the fractional coverage within a given reconstruction. Our data show that the (3X1), (1X6},and (4X6) reconstructions are at least partly determined by kinetics, since they can only be obtained by following specific heating or cooling procedures under very low As4 flux. More generally, it is possible to employ this optical technique to determine surface atomic and electronic structure. Because RD spectra can be obtained with the surface in any transparent ambient, the database that we have established here provides a new approach for elucidating surface reconstructions of (001) GaAs and hence the dynamics of surface reactions in non-UHV environments.
Japanese Journal of Applied Physics, 1998
The reflectance difference (RD) spectra of nine GaAs(001) surface reconstructions, (2×4)β2, (2×4)α, (2×4)γ2, (2×4)β1, (2×4)γ1 and c(4×4) reconstructions on As-rich surface and (4×2)β2, (4×2)α and (4×2)β1 reconstructions on Ga-rich surface, were studied by using the nearest-neighbor s p 3 s * tight-binding method. The surface atomic positions and the tight-binding interaction parameters were obtained by the ab inito pseudopotential calculations. We found that the RD spectra have considerably different features between As- and Ga-rich surface reconstructions. The RD spectra of As-rich surfaces are mainly understood by transitions between top As-dimer states, while the RD spectra of Ga-rich surfaces are explained by the surface electronic states resulting from the sinkage of surface Ga atoms into bulk layers. These calculations are compared with the results of recent experiments.
Physical Review B, 1995
Surface-shift low-energy photoelectron diffraction has recently been revealed as a powerful tool for the determination of surface structures. We have applied this method to study clean and hydrogenated (1/4 of monolayer) GaAs(110) surfaces. A recently developed renormalized multiplescattering theory [M. Biagini, Phys. Rev. B 48, 2974 (1993)j has been applied to the interpretation of As 3d polar spectra. Numerical computations have been carried out for several surface geometries, corresponding to different buckling angles and surface bond lengths. We have obtained a buckling angle u = 26' and 6 for clean and hydrogenated surfaces, respectively. As far as surface bond lengths are concerned, changes within +2'Fc for the clean surface and ideal bond lengths for the hydrogenated surface were found.