Reflectance anisotropy of reconstructed GaAs (001) surfaces (original) (raw)
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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.
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.
Optical characterisation of semiconductor surfaces and interfaces
Progress in Surface Science, 1995
Recent developments in optical spectroscopy applied to semiconductor surfaces and interfaces are reviewed. It is shown that, by exploiting the underlying physics of the various techniques, or by exploiting special material structures, submonolayer sensitivity can be obtained using photons as both probe and signal. Examples of the use of spectroscopic ellipsometry, surface differential reflectivity, surface photoabsorption, reflection anisotropy spectroscopy, Raman
Physical Review B
The optical anisotropy of c(4ϫ4), (2ϫ4), (2ϫ6) and (4ϫ2) reconstructed GaAs͑001͒ surfaces has been calculated from first principles. It consists of surface structure-dependent features originating from electronic transitions in the uppermost surface layers and of anisotropy peaks close to the E 1 and E 0 Ј/E 2 bulk critical point energies. The latter contributions are nearly structure independent and arise from transitions between surface-modified bulk electronic states. For the smaller reconstructions the influence of surface electric fields on the optical anisotropy is studied. We find that the linear electro-optic effect modifies mainly the optical anisotropy from the bulk atomic layers, resulting in changes of the reflectance anistropy spectroscopy signal which are strongly reconstruction dependent, however. Changes of the atomic relaxation due to surface electric fields are less important for the modification of the optical signal than the polarization of the electron wave functions.
Anisotropy of surface optical properties from first-principles calculations
Physical Review B, 1990
The optical properties of GaAs(110) and GaP(110) surfaces are studied by means of self-consistent local-density calculations. A very large contribution to the reflectance anisotropy is found to be related to transitions which do not involve surface states. These transitions give a substantialyet smallercontribution also to the differential reflectivity. Comparison is made with relevant experimental data.
Detection of surface states anisotropies at GaAs(001)(2 × 4) decapped surfaces
Physica Status Solidi B-basic Solid State Physics, 2005
The surface or bulk origin of the optical anisotropies detected by reflectance anisotropy spectroscopy (RAS) at GaAs(001)(2 × 4) surfaces has been extensively investigated in the last years and a quite general agreement has been reached that the dominating character would be bulk-like. Nevertheless, a very recent paper [F. Arciprete et al., Phys. Rev. B 69, 081308(R) (2004)] has again issued the presence of surface states contributions in optical anisotropies, revealing a structure at 2.5 eV due to surface states, in addition to the well known features around 2.9 eV and 4.5 eV related to the bulk critical points E1 and E0′. We have carried out a new experiment to prove this conclusion by following the changes in the optical anisotropy of a GaAs(001)(2 × 4) surface in the range 2.0–5.0 eV induced by Ag/Sb-codeposition. The interface Ag/GaAs(001) is known to be not reactive. Due to its surfactant effect, codeposition of Sb leads to a nearly epitaxial growth of the Ag overlayer. We sho...
Optical spectroscopy of (001) GaAs and AlAs under molecular-beam epitaxy growth conditions
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1991
Reflectance-difference (RD) studies were performed on variously reconstructed (001) GaAs and AlAs surfaces. The spectra of the (2 X 4) and (4 X 2) reconstructions on (001) GaAs show prominent features due to electronic transitions between lone-pair orbitals and dimer states, as previously identified by theoretical calculations. The spectra of the c (4 X 4) reconstructions on (001) GaAs and AlAs show similar features that we also interpret in terms of surface dimer excitations. These dimer features provide a capability of obtaining real-time, in situ information of dynamics on polar surfaces.
Optical anisotropy of organic layers on GaAs(001)
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2001
The application of the linear-optical, polarization sensitive methods, in situ reflectance anisotropy spectroscopy ͑RAS͒, and ex situ spectroscopic ellipsometry, for the characterization of organic layers is discussed and the results of the investigation of 3,4,9,10-perylenetetracarboxylic dianhydride ͑PTCDA͒ layers on sulfur passivated GaAs͑001͒ surfaces are presented. The organic layers were grown via organic molecular beam deposition at room temperature. The RA spectrum of the sulfur terminated GaAs surface shows a derivative like feature at E 1 gap and a feature in the higher energy range related to E 2 of bulk GaAs. Upon the PTCDA deposition, additional features appear in the spectra which can be attributed to PTCDA while the GaAs feature near E 1 remains unchanged indicating that the surface reconstruction stays intact. The imaginary part of the pseudo-dielectric function is found to be angular dependent. This dependence also changes as a function of azimuthal angle. While the first can be well described using existing models for optical uniaxial layers, the latter is likely to be related to in-plane optical anisotropy.
Optical anisotropy of cyclopentene terminated GaAs(001) surfaces
Applied Physics A, 2007
Up to now most of the experimental work regarding the adsorption of organic molecules has been concerned with silicon. Here we study the interface formation on a III-V-semiconductor, GaAs(001). We show that reflectance anisotropy spectroscopy (RAS) is a sensitive technique for investigating the interface formation between organic molecules and semiconductor surfaces. With RAS it is possible to determine the surface reconstruction and the structural changes at the interface during the deposition of organic molecules. These changes and the underlying adsorption process are discussed here for the adsorption of cyclopentene on GaAs(001)c(4 × 4), (2 × 4) and (4 × 2).