Razvigor Ossikovski

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.

Differential matrix formalism for depolarizing anisotropic media

Azzams differential matrix formalism [J. Opt. Soc. Am. 68, 1756 (1978)], originally developed for longitudinally inhomogeneous anisotropic nondepolarizing media, is extended to include depolarizing media. The generalization is physically interpreted in terms of means and uncertainties of the elementary optical properties of the medium, as well as of three anisotropy absorption parameters introduced to describe the depolarization. The formalism results in a particularly simple mathematical procedure for the retrieval of the elementary properties of a generally depolarizing anisotropic medium, assumed to be globally homogeneous, from its experimental Mueller matrix. The approach is illustrated on literature data and the conditions of its validity are identified and discussed.

Forward and reverse product decompositions of depolarizing Mueller matrices

Because of the noncommutativity of the matrix product, the three factors into which a depolarizing Mueller matrix is decomposed, i.e., the diattenuator, the retarder, and the depolarizer, form six possible products grouped into two families, as already pointed out [J. Opt. Soc. Am. A13, 1106 (1996); Opt. Lett.29, 2234 (2004)]. We show that, apart from the generalized polar decomposition generating the first family of products, there exists a dual decomposition belonging to the second family. The mathematical procedure for this dual decomposition is given, and the symmetry existing between the two decompositions is pointed out. The choice of the most appropriate decomposition for a given practical optical arrangement is likewise discussed and illustrated by simple examples.

Recent advances in germanium emission [Invited]

The optical properties of germanium can be tailored by combining strain engineering and n-type doping. In this paper, we review the recent progress that has been reported in the study of germanium light emitters for silicon photonics. We discuss the different approaches that were implemented for strain engineering and the issues associated with n-type doping. We show that compact germanium emitters can be obtained by processing germanium into tensile-strained microdisks.

Measurement of the absorption edge of thick transparent substrates using the incoherent reflection model and spectroscopic UV)visible)near IR ellipsometry

A model taking into account the incoherent reflection in a thick transparent substrate approx. 1 mm is described and tested. The incoherent model makes it possible to calculate the averaged elements of the Mueller matrix describing the . sample, for comparison with data obtained by Spectroscopic Phase Modulated Ellipsometry SPME . By performing PME in two different configurations, the degree of polarisation is calculated from the measured intensities and compared to the theory. The strong transition from incoherent to coherent reflection at the onset of the extinction or absorption edge, makes it y5. possible to measure extremely weak extinction coefficients k ; 10 using ellipsometry. In particular, the electronic absorption edge in the UV)visible region, giving the transition from incoherent to coherent reflection, is found to be . . adequately modelled by the Forouhi)Bloomer F and B or the Tauc)Lorentz TL dispersion formulas. Industrial applica- tions of ellipsometry often involve transparent substrates and examples of characterisation of thin films on glass are given. Q 1998 Elsevier Science S.A.

Control of tensile strain in germanium waveguides through silicon nitride layers

Germanium ridge waveguides can be tensilely strained using silicon nitride thin films as stressors. We show that the strain transfer in germanium depends on the width of the waveguides. Carrier population in the zone center Γ valley can also be significantly increased when the ridges are oriented along the 〈100〉 direction. We demonstrate an uniaxial strain transfer up to 1% observed on the room temperature direct band gap photoluminescence of germanium. The results are supported by 30 band k·p modeling of the electronic structure and the finite element modeling of the strain field.

High quality tensile-strained n-doped germanium thin films grown on InGaAs buffer layers by metal-organic chemical vapor deposition

We show that high quality tensile-strained n-doped germanium films can be obtained on InGaAs buffer layers using metal-organic chemical vapor deposition with isobutyl germane as germanium precursor. A tensile strain up to 0.5% is achieved, simultaneously measured by x-ray diffraction and Raman spectroscopy. The effect of tensile strain on band gap energy is directly observed by room temperature direct band gap photoluminescence.

Billion-Fold Increase in Tip-Enhanced Raman Signal

A billion-fold increase in the Raman signal over conventional tip-enhanced Raman spectroscopy/microscopy (TERS) is reported. It is achieved by introducing a stimulating beam confocal with the pump beam into a conventional TERS setup. A stimulated TERS spectrum, closely corresponding to its spontaneous TERS counterpart, is obtained by plotting the signal intensity of the strongest Raman peak of an azobenzene thiol self-assembled monolayer versus the stimulating laser frequency. The stimulated TERS image of azobenzene thiol molecules grafted onto Au ⟨111⟩ clearly shows the surface distribution of the molecules, whereas, when compared to the simultaneously recorded surface topography, it presents an image contrast of different nature. The experimentally obtained stimulated gain is estimated at 1.0 × 10(9), which is in reasonable agreement with the theoretically predicted value. In addition to the signal increase, the signal-to-noise ratio was 3 orders of magnitude higher than in conventional spontaneous TERS. The proposed stimulated TERS technique offers the possibility for a substantially faster imaging of the surface with respect to normal TERS.

Determining the stress tensor in strained semiconductor structures by using polarized micro-Raman spectroscopy in oblique backscattering configuration

We present a characterization technique for the determination of the stress tensor as well as of the crystallographic orientation of strained semiconductor structures. The technique is based on a polarized oblique incidence micro-Raman experiment in a backscattering configuration. A methodology relating the stress-induced frequency shifts and linewidths of the phonon peak to the stress tensor components within the adopted experimental configuration was developed. The method consists in monitoring the variations of the stress-sensitive peak frequencies and linewidths while rotating stepwise the sample about its normal. The practical application of the technique is illustrated on a Si∕SiGe sample microelectronic structure demonstrating a full plane stress tensor determination.

Anisotropic incoherent reflection model for spectroscopic ellipsometry of a thick semitransparent anisotropic substrate.

An anisotropic incoherent reflection model for the Mueller matrix elements of an optically thick uniaxial anisotropic semitransparent substrate with its anisotropy axis along its surface normal is developed. The Mueller matrix elements are measured by phase-modulated spectroscopic ellipsometry (SE) and compared with incoherent reflection model simulations. In the case of a sapphire substrate the oscillations observed are accurately modeled, and, in addition, the oscillating degree of polarization is correctly predicted. A straightforward generalization of the optical model, in the case of an arbitrary stack of layers containing a thick anisotropic semitransparent substrate, is also proposed and experimentally validated. The model is further applied to study the anisotropic dielectric function of a semi-insulating 4H-SiC wafer. An approximation based on a simple variation in the optical transition element is proposed to model the SiC birefringence. In conclusion, SE is shown to be a powerful alternative for investigating and predicting the behavior of optically thick birefringent materials.