Reflectance anisotropy of reconstructed GaAs (001) surfaces (original) (raw)
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).
Real time in situ observation of (001)GaAs in OMCVD by reflectance difference spectroscopy
Applied Surface Science, 1992
We report the first direct observation of reconstructions of semiconductor surfaces in aUntJspherle pressure tAP) environments. We use reflectance difference spectroscopy (RDS), a surface-sensitive optical probe, lu bridsc the gap helweell ultrahigh vacuum (UHV) and AP, and show Ihat the primary surface recons~rucaons thai occur on (0el)13aAs surfaces in UHV also occur in the AP environments used with ~rganometallic chem;cM vapor depositioB tOMCVD). Our results fustily the applicability of the results of UHV surface science to understanding surface~ under non-UHV environments. Our results also show that during OMCVD growth conditions the surface is termina 4 with muhilarers of As, ctmtrary to generalb accepted models. We also apply our newly devduped approach, multl-transiea, speoroscopy tMTS), to the study of atomic layer epitaxy (ALE), Using MTS. we obse~e surface spcclra within a time resolution of 100 ms during actual &LE growth cycles, thus alluwing the dynamics of surface reacaons to he invesligaled.
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]
Journal of Applied Physics, 1995
Using variable angle spectroscopic ellipsometry, optical constants for AlAs (1.4-5.0 eV) are presented which are simultaneously compatible with measured data from four different samples. The below-gap index values are compatible with published prism measured values. The second derivative spectrum are compatible with published values above the direct band gap. The AlAs spectra is Kramers-Kromg self-consistent over the measured range and is compatible with published values from 0.6 to 1.4 eV. The optical constants for thin ((50 A) GaAs caps on AlAs are shown to be different from bulk GaAs values and require special consideration when fitting ellipsometric data. For the thin GaAs caps, the Et and E,+A, critical-point structure is shifted to higher energies as previously observed for GaAs quantum wells. Bulk AlAs optical constants are shown to be different from those of a thin (-20 A) AlAs barrier layer embedded in GaAs. The thin barrier layer exhibits a highly broadened critical-point structure. This barrier broadening effect (AlAs) and the thin cap shifting effects (GaAs) have implications for in situ growth control schemes which make use of the E, and E, +A, critical-point region.
New Probe of the Optical Properties of Surfaces
1983
We have developed a new technique, photothermal displacement spectroscopy, for studying the optical and thermal properties of surfaces. The ability to distinguish surface and bulk optical absorptions is demonstrated. The signal is directly proportional to the surface absorption coefficient and is insensitive to variations in the real part of the index of refraction.