Spectroscopic ellipsometry and polarimetry for materials and systems analysis at the nanometer scale: state-of-the-art, potential, and perspectives

This paper discusses the fundamentals, applications, potential, limitations, and future perspectives of polarized light reflection techniques for the characterization of materials and related systems and devices at the nanoscale. These techniques include spectroscopic ellipsometry, polarimetry, and reflectance anisotropy. We give an overview of the various ellipsometry strategies for the measurement and analysis of nanometric films, metal nanoparticles and nanowires, semiconductor nanocrystals, and submicron periodic structures. We show that ellipsometry is capable of more than the determination of thickness and optical properties, and it can be exploited to gain information about process control, geometry factors, anisotropy, defects, and quantum confinement effects of nanostructures

Ab initio calculation of the reflectance anisotropy of GaAs(110)

We compute the optical properties of the (110) 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 them) and in the longitudinal gauge (where they are automatically included). The two calculations, although giving different dielectric functions, yield the same reflectance anisotropy, which compares well with experimental data and with previous theoretical results

Polarization-dependent surface transitions at Sb/GaAs (110)

We have investigated, both experimentally and theoretically, the optical properties of an epitaxial monolayer of Sb deposited on GaAs(110). In particular we have studied the polarization-dependence of Differential Reflectance. Good agreement between the experimental results and theory has been found. Several spectral features observed in the visible energy range have been interpreted, on the basis of the theoretical results, as optical transitions taking place at different symmetry points of the surface Brillouin zone

Theory of the temperature dependent dielectric function of semiconductors: from bulk to surfaces. Application to GaAs and Si

novel, efficient method for calculating the temperature dependencies of the linear dielectric functions of semiconductor systems and its application are presented. The method follows an intuitive and natural path with ab-initio finite temperature molecular dynamics providing the thermally perturbed atomic configurations, which are used as structural inputs for calculating the dielectric function. The effect of lattice dynamics, including quantum zero point vibration, on the electronic bands and dielectric function of crystalline (c-) GaAs and Si as well as hydrogenated amorphous Si (a-Si:H) is discussed. Our theoretical results for bulk c-GaAs and c-Si in the range from 0 to 1000 K are in good overall agreement with highly accurate ellipsometric measurements. The implementation of the method resolves a serious discrepancy in energy and line shape between experiment and the latest optical models, all of which neglect lattice dynamics, and provides information on the indirect gap and indirect optical transitions in c-Si. For a-Si:H, the calculated temperature dependent optical response combined with the vibrational spectroscopy provides detailed insight into electronic, dynamical properties, and stability of this important prototypical amorphous semiconductor material. At semiconductor surfaces, dynamical effects are expected to be even more pronounced due to reduced atom coordination and reconstruction. This is demonstrated for C(111) 2 × 1, an intensively studied but controversial surface of the quantum diamond crystal

Ge/GaAs(001) interface formation investigated by reflectance anisotropy spectroscopy

The formation of the Ge/GaAs(001) interface has been investigated following the transformation of an As-dimer terminated GaAs(001)(2 X 4) surface into a Ge-Ga-dimer terminated (1 X 2) reconstruction and the subsequent deposition up to 10 ML of Ge. The modification of the surface atomic geometry and the related electronic structure has been monitored by reflectance anisotropy spectroscopy (RAS) and low-energy electron diffraction. Experimental results are compared to density-functional-theory-local-density-approximation and tight-binding calculations of the surface structure and optical response, respectively. The comparison between calculated and measured RAS spectra allows us to show that the (2 X 4) structure transforms into a well-ordered (1 X 2) passing through a disordered (2 X 4) phase while a previously proposed intermediate (2 X 1) structure is ruled out. At higher Ge coverages, surface and Ge/GaAs-interface contributions to the optical spectra are separated by surface modification through exposure to atmosphere. A interface contribution is identified between 1.5 eV and 2.5 eV, almost identical in line shape and amplitude to the RAS features on the Ge-Ga-dimer terminated GaAs surface. This finding demonstrates that the backbonds of the Ge-Ga-dimers, present at the Ge-Ga-dimer terminated surface as well as at the Ge/GaAs interface, determine the optical anisotropy, whereas the Ge-Ga-dimer bond itself does not contribute significantly. [S0163-1829(99)12315-4]

Surface states and resonances on Al(110): Ultraviolet photoemission spectroscopy and ab initio calculations

The electronic structure of a clean (110) surface of crystalline aluminum is investigated experimentally by measuring the angle-resolved ultraviolet photoemission spectra at high-symmetry points of the surface Brillouin zone for photon energies in the range 10-29 eV. The binding energies and dispersions of several features in the experimental spectra are determined. The experimental data are interpreted by means of an ab initio full-potential linear-augmented plane-wave calculation of the surface electronic structure based on density functional theory. Two of the features in the spectra are identified as being due to emission from previously unobserved surface states and surface resonances. The effects of surface relaxation on the surface electronic structure are discussed

Sb-induced (1×1) reconstruction on Si(001)

We combine low-energy electron diffraction and reflectance anisotropy spectroscopy (RAS) with ab initio calculations of the geometry, band structure, and optical anisotropy to investigate the adsorption of Sb on vicinal Si(001) (1x2). We focus, in particular, on the controversy concerning the Si(001)-(1x1)-Sb surface. On the basis of total-energy and band-structure calculations, we find that the Sb-undimerised model is unstable and metallic, while experimentally the (1x1) Sb shows no evidence of a Fermi edge. In contrast, the dimerised (2x1)-Sb and c(2x2)-Sb reconstructions are found to be semiconducting with a minimal difference in total energy. Furthermore, the RAS spectra calculated for both dimerised reconstructions show strong similarities to one another, and agree well with the experimental RAS data for the Sb-induced (1x1)-Sb surface, with a dominant feature centered at 3.7 eV. We report that these findings are compatible with the (1x1)-Sb surface comprising a mixture of the Sb-dimer-terminated (2x1)-Sb and c(2x2)-Sb structures

Electronic structure of the GaAs(001)2x4 and GaAs(110) surfaces studied by high-resolution electron-energy-loss spectroscopy

We compare, by high-resolution electron-energy-loss spectroscopy (HREELS), the electronic structure of the GaAs(110)1x1 surface and that of the GaAs(001)2x4 As-rich surface in the energy-loss region 0.5-5 eV. The HREEL spectra are interpreted in terms of realistic calculations. The spectral features above the gap are assigned to electronic transitions involving surface and/or bulk states. Losses at energies within the gap are associated to defect states at the surface. [S0163-1829(98)51236-2]

Electronic structure of the GaAs(001)2x4 and GaAs(110) surfaces studied by high-resolution electron-energy-loss spectroscopy

We compare, by high-resolution electron-energy-loss spectroscopy (HREELS), the electronic structure of the GaAs(110)1x1 surface and that of the GaAs(001)2x4 As-rich surface in the energy-loss region 0.5-5 eV. The HREEL spectra are interpreted in terms of realistic calculations. The spectral features above the gap are assigned to electronic transitions involving surface and/or bulk states. Losses at energies within the gap are associated to defect states at the surface. [S0163-1829(98)51236-2]