Infrared Reflectivity Data Research Articles

Optical properties of highly n-doped germanium obtained by in situ doping and laser annealing

High n-type doping in germanium is essential for many electronic and optoelectronic applications especially for high performance Ohmic contacts, lasing and mid-infrared plasmonics. We report on the combination of in situ doping and excimer laser annealing to improve the activation of phosphorous in germanium. An activated n-doping concentration of 8.8 × 1019 cm−3 has been achieved starting from an incorporated phosphorous concentration of 1.1 × 1020 cm−3. Infrared reflectivity data fitted with a multi-layer Drude model indicate good uniformity over a 350 nm thick layer. Photoluminescence demonstrates clear bandgap narrowing and an increased ratio of direct to indirect bandgap emission confirming the high doping densities achieved.

Preparation of Nb-doped Anatase Type TiO2 Epitaxial Thin Films and Excitation of Surface Plasmon Polaritons

We have fabricated highly crystallized thin films of niobium-doped anatase type titania (Ti1−xNbxO2) to examine the relationship between the electronic transport properties and the plasmonic response. Ti1−xNbxO2 thin films were epitaxially grown on LaTiO3 substrates by using pulsed laser deposition. Attenuated total reflectance spectra in the infrared (IR) region measured using the Otto configuration show a dip for p-polarized light, corresponding to an excitation of surface plasmon polaritons. The IR reflectivity data can be well reproduced by the theoretical calculation based on the Fresnel model, in which the dielectric function of Ti1−xNbxO2 can be modeled by the combination of a Lorentz term and a Drude term. The real part of dielectric function for Ti1−xNbxO2 (x = 0.03) is negative at the wavelengths longer than 2.78 μm in the IR region.

Structure and Microwave Dielectric Properties of Low Firing Bi2Te2W3O16 Ceramics

Dense Bi2Te2W3O16 ceramics were prepared by the conventional solid‐state reaction route. X‐ray diffraction data show the room‐temperature (RT) crystal symmetry of Bi2Te2W3O16 to be well described by the centrosymmetric monoclinic C2/c space group [a = 21.280(5) Å, b = 5.5663(16) Å, c = 12.831(3) Å and β = 124.014(19)° and Z = 4]. Raman spectroscopy analyses are in broad agreement with space group assignment, but also revealed the presence of Bi2W2O9 as a secondary phase. This phase is present as plate‐like grains embedded on a fine‐grained equiaxed matrix, as revealed by scanning electron microscopy. From the fitting of infrared reflectivity data the relative permittivity, εr, was estimated as 34.2, and the intrinsic quality factor, Qu × f as 57 500 GHz. At RT and microwave frequencies, Bi2Te2W3O16 ceramics sintered at 720°C for 6 h exhibit εr ~ 34.5, Qu × f = 3173 GHz (at 7.5 GHz), and temperature coefficient of resonant frequency, τf = −92 ppm/°C. This shows a good agreement between the estimated and measured εr values, but also shows that, in principle, the dielectric losses of the ceramics are of extrinsic origin.

Optical response of DyN

We report measurements of the optical response of polycrystalline DyN thin films. The frequency-dependent complex refractive index in the near IR-visible-near UV was determined by fitting reflection/transmission spectra. In conjunction with resistivity measurements, these identify DyN as a semiconductor with an optical energy gap of 1.2 eV. When doped with nitrogen vacancies it shows free carrier absorption and a blue-shifted gap associated with the Moss-Burstein effect. The refractive index of 2.0 ± 0.1 depends only weakly on energy. Far infrared reflectivity data show a polar phonon of frequency 280 cm−1 and a dielectric strength of Δε=20.

Atomically smooth and single crystalline indium tin oxide thin film with low optical loss

AbstractWe have fabricated a highly crystalline thin film of indium tin oxide (ITO) to examine the relationship between properties of charge carriers and their collective plasmonic response. The ITO thin film with atomically flat surface was epitaxially grown on a yittria‐stabilized zirconia substrate by using pulsed laser deposition. Attenuated total reflectance spectra for the infrared (IR) region in the Otto configuration show a dip for p ‐polarized light, corresponding to an excitation of surface plasmon polaritons. The IR reflectivity data can be well reproduced by the theoretical calculation based on the Fresnel model, in which the dielectric function of ITO is deduced from the Drude theory using the carrier density and mobility obtained by Hall measurement. The high carrier mobility in single crystalline ITO thin film is found to result in a significantly low optical loss in the IR region (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermal diffusivity of alkali and silver halide crystals as a function of temperature

The phonon component of thermal diffusivity (D) for ten synthetic single-crystals (LiF, NaCl, NaI, NaI:Tl, KCl, KBr, CsI, CsI:Tl, AgCl, and AgBr) with the B1 and B2 structures was measured from ambient temperature (T) up to ∼1093 K using contact-free, laser-flash analysis, from which effects of ballistic radiative transfer were removed. We investigated optical flats from different manufacturers as well as pellets made from compressed powders of most of the above chemical compositions plus LiI, NaBr, KI, RbCl, RbBr, RbI, CsCl, CsBr, and AgI. Impurities were characterized using various spectroscopic methods. With increasing T,D decreases such that near melting the derivatives ∂D/∂T are low, −0.0006±0.0004 mm2 s−1 K−1. Our results are ∼16% lower than D298 previously obtained with contact methods, which are elevated by ballistic radiative transfer for these infrared (IR) windows, and are well described by either D−1 following a low order polynomial in T, or by D−1∝T+n, where n ranges from 1.0294 to 1.9429. Inverse correlations were found between D298 and both density and thermal expansivity (α). Primitive lattice constant times compressional velocity correlates directly with D but changes much more slowly with temperature. Instead, D(T) is proportional to (TαL)−1 from ∼0 K up to the limit of measurements, in accord with these physical properties being anharmonic. On average, the damped harmonic oscillator–phonon gas model reproduces D298 based on two physical properties: compressional velocity and the damping coefficient (Γ) from analysis of IR reflectivity data. Given large uncertainties in Γ(T), D−1(T) is reproduced for LiF, NaCl, MgO, and the silver halides, for which IR reflectivity data are available. Our correlations show that optical phonons largely govern heat transport of insulators, and permit prediction of D and thus thermal conductivity for simple, diatomic solids.

Orientation-switching transition and ferroelectricity in betaine arsenate

This paper reports a detailed investigation of the low frequency dielectric relaxation ofbetaine arsenate near the ferroelectric phase transition. The dielectric relaxation data arecomplemented with polarized infrared reflectivity data taken at low temperatures. Thereported results allow us to identify several low frequency modes that clarifythe complex behaviour of the dielectric response near the Curie temperatureTc2≈120 K. It is suggested that the important slow dynamics observed is linked to the reorientationof the betaine molecular group. The roles of the different molecular units in the structuralchanges are briefly discussed and a new and more complex phase transition sequence isproposed.

OPTICAL CONSTANTS OF SILICON CARBIDE FOR ASTROPHYSICAL APPLICATIONS. II. EXTENDING OPTICAL FUNCTIONS FROM INFRARED TO ULTRAVIOLET USING SINGLE-CRYSTAL ABSORPTION SPECTRA

Laboratory measurements of unpolarized and polarized absorption spectra of various samples and crystal stuctures of silicon carbide (SiC) are presented from 1200--35,000 cm$^{-1}$ ($\lambda \sim$ 8--0.28 $\mu$m) and used to improve the accuracy of optical functions ($n$ and $k$) from the infrared (IR) to the ultraviolet (UV). Comparison with previous $\lambda \sim$ 6--20 $\mu$m thin-film spectra constrains the thickness of the films and verifies that recent IR reflectivity data provide correct values for $k$ in the IR region. We extract $n$ and $k$ needed for radiative transfer models using a new ``difference method'', which utilizes transmission spectra measured from two SiC single-crystals with different thicknesses. This method is ideal for near-IR to visible regions where absorbance and reflectance are low and can be applied to any material. Comparing our results with previous UV measurements of SiC, we distinguish between chemical and structural effects at high frequency. We find that for all spectral regions, 3C ($\beta$-SiC) and the $\vec{E}\bot \vec{c}$ polarization of 6H (a type of $\alpha$-SiC) have almost identical optical functions that can be substituted for each other in modeling astronomical environments. Optical functions for $\vec{E} \| \vec{c}$ of 6H SiC have peaks shifted to lower frequency, permitting identification of this structure below $\lambda \sim4\mu$m. The onset of strong UV absorption for pure SiC occurs near 0.2 $\mu$m, but the presence of impurities redshifts the rise to 0.33 $\mu$m. Optical functions are similarly impacted. Such large differences in spectral characteristics due to structural and chemical effects should be observable and provide a means to distinguish chemical variation of SiC dust in space.

Pressure-induced metallization of silane

There is a great interest in electronic transitions in hydrogen-rich materials under extreme conditions. It has been recently suggested that the group IVa hydrides such as methane (CH(4)), silane (SiH(4)), and germane (GeH(4)) become metallic at far lower pressures than pure hydrogen at equivalent densities because the hydrogen is chemically compressed in group IVa hydride compounds. Here we report measurements of Raman and infrared spectra of silane under pressure. We find that SiH(4) undergoes three phase transitions before becoming opaque at 27-30 GPa. The vibrational spectra indicate the material transforms to a polymeric (framework) structure in this higher pressure range. Room-temperature infrared reflectivity data reveal that the material exhibits Drude-like metallic behavior above 60 GPa, indicating the onset of pressure-induced metallization.

Elasticity and lattice vibrational properties of transparent polycrystalline yttrium–aluminium garnet: Experiments and pair potential calculations

Brillouin light scattering, Raman light scattering and visible–infrared reflectometry techniques have been used to investigate, respectively, the elastic properties, the phonons and the optical properties of bulk textured polycrystalline yttrium–aluminum garnet doped with 2 at% neodymium obtained by the sintering of commercial oxides. From the analysis of the observed bulk longitudinal and transverse acoustic modes with the knowledge of the refractive index 1.81 inferred from the visible reflectometry, the two independent effective elastic constants of the isotropic polycrystal C 11 = 362 GPa and ( C 11 − C 12)/2 = 121 GPa are determined leading to the value of the bulk modulus B = ( C 11 + 2 C 12)/3 = 200 GPa. The ratio ɛ 0/ ɛ ∞ = 3.1 and the optic permittivity ɛ ∞ = 3.46 are derived from the infrared reflectivity data. Pair potential calculations of the three single crystal elastic constants c 11 = 340, c 12 = 127 and c 44 = 112 GPa, of the bulk modulus B = ( c 11 + 2 c 12)/3 = 198 GPa, of the zone-center (Γ) phonons and of the permittivity function provide good comparison with our experimental results.

Zone center optical phonons in AlxGa1−xN mixed crystals

Infrared reflectivity and Raman spectroscopy were used as two complementary experiments to probe the zone center optical phonons in the aluminum gallium nitride (AlxGa1−xN) systems. A careful analysis of the infrared reflectivity data using the Kramers-Kronig technique and classical dispersion theory gives several resonance modes shifting in frequency with the mole fraction of the aluminum content in the alloy. A signature of an additional resonance mode appears for x∼0.58. A geometrical arrangement was performed to observe the E2 and A1(LO) phonons from the first order Raman scattering. The variation of the frequencies of these phonons was followed in the compositional range investigated. In addition to these two phonons observed from the Raman scattering, a new phonon mode shows up for x∼0.4. Our experimental results were compared with a theoretical study of the lattice dynamics of random AlxGa1−xN alloy based on the generalization of the modified random-element isodisplacement and rigid-ion model in order to interpret the experimentally observed resonance modes. The two-mode behavior in the AlxGa1−xN alloy was observed only for the E1(TO) optical mode.

Far‐infrared synchrotron radiation spectroscopy of solids in normal and extreme conditions

New opportunities in solid-state physics are offered by SINBAD (Synchrotron INfrared Beamline At DAFNE), the infrared beamline operational at DAΦNE, the storage ring of the Laboratori Nazionali di Frascati of the INFN. During 2003 several experiments, including those supported by the European TARI program, have been successfully performed at SINBAD. In this work we present the preliminary results of high resolution far infrared reflectivity data collected in different ZnxCdyHg(1–x–y)Te quaternary alloys as a function of temperature. The first far-IR investigation of Colossal Magnetoresistance manganites at high pressures, using a diamond anvil cell is also presented. Indeed, FT-IR spectroscopy is a powerful tool for the investigation of insulating-to-metal transitions and charge ordering phenomena that may occur in transition metal oxides. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Raman scattering investigation of cesium plumbochloride, CsPbCl3, phase transitions

AbstractWe report a Raman scattering investigation of CsPbCl3 as a function of temperature in four different scattering configurations allowing us to obtain the various irreducible representations of the appropriate symmetry groups describing the substance in its successive phase transitions: cubic, tetragonal, orthorhombic and monoclinic or orthorhombic. We identify the correct ‘parentage’ of the observed modes with respect to infrared reflectivity data reported in the literature in accord with the Lyddane–Sachs–Teller relation, which was not fulfilled in previous assignments. We demonstrate the presence of strong correlation chains, which maintain the compound in a pseudo‐cubic state as far as x‐ray, infrared and Raman spectroscopy are concerned. The intensity of the related central peak was analysed on the basis of a Debye‐type relaxation as a function of temperature; the results show perfect correspondence of its variations and the temperatures of the phase transitions. In addition, an order–disorder phase transition is evidenced at low temperature, 193 K (−80 °C). Copyright © 2003 John Wiley & Sons, Ltd.

Optical Characterization of Donor Doped Ternary Alloy Ga 1-x N x As and GaN-Ga 1-x N x As MQW by Using Infrared Fourier Transform Spectroscopy

In this work polarized infrared Fourier transform spectroscopy is employed to study the electronic and optical properties of doped Ga1-xNxAs ternary alloy and GaN-Ga1-xNxAs MQW. We have analyzed the far infrared spectra of GaN-GaNAs MQW by using a simple macroscopic theory base on effective medium approximation model. The dispersion curve of coupled LO phonon- plasmon modes were calculated from the polarized infrared reflectivity data. The GaNAs layer shows two-mode behavior in the infrared spectral range, a GaAs-like and a GaN-like sublattices. We detect the transverse optic phonon of GaN sublattice around 475 cm-1. The origin of the sharp feature in p-polarization reflectivity about 300 cm-1 as well as the dip at LO phonon frequency of GaAs sublattice are due to Brewster mode. The Brewster mode is couple strongly to plasmon mode. Attenuated total reflection spectroscopy has been used to excite and investigate surface plasmon and surface polariton.

Infrared Reflectivity and Transport Investigations of GaN Single Crystals and Homoepitaxial Layers

The aim of this paper is to examine infrared reflectivity as a nondestructive characterization for gallium nitride bulk and its homoepitaxial epilayers. For that purpose, we have compared infrared reflectivity data (electron concentration and optical mobility) with the results of low-field Hall measurements. We examined various bulk GaN crystals and homoepitaxial layers grown on highly conducting GaN substrates. In our research, we paid special attention to the polarity of the sample surface as it influences the electronic properties of the homoepitaxial layers.

Raman spectra of the chalcopyrite compound CuInTe2

The lattice vibrational modes of the chalcopyrite compound CuInTe2 have been obtained at several temperatures by the unpolarized Raman spectra. Lines observed at 48, 74, 129, 138, 155, and 185 cm−1, identified with E modes, and at 60, 106, and 170 cm−1, assigned to B2 modes, agree quite well with the peaks reported from infrared reflectivity data. On the other hand, using the available theoretical models, the peaks that appear at 123 cm−1 and those observed around 65, 116, and 223 cm−1, which are only Raman active, are assigned to the A1 and B1 modes, respectively.

Kramers-kronig type analysis of short spectral range reflection spectra

Abstract This paper describes a new development in the use of the Kramers-Kronig method for the analysis of infrared reflection spectra. It is shown that precise and useful data can be obtained from even a small region of the reflection spectrum when appropriate boundary conditions are carefully applied. In particular it is shown how the use of boundary conditions which reduce to a minimum the calculated phase change on reflection of the radiation at relatively low absorption regions at the high and low energy limits of the studied region, adds significantly to the reliability of the calculations. Infrared reflectivity data for ammonium chloride and bromide in the spectral range 1000 to 1700 cm −1 are used to illustrate the method. A frequency precision of v ± 0.15 cm −1 is obtained for band-center frequencies of equivalent absorption spectra calculated from the observed reflection spectra. This has allowed a detailed study of the small but significant changes that take place in this internal mode frequency as the crystal is made to pass through its λ-transition. It has also shown how a short section of an IR reflection spectrum from a sample held within a hostile environment (e.g. within a high pressure enclosure,) can be used to derive precise data on the properties of such a sample.

Far infrared reflectivity off FeF2

Oblique-incidence (45°) FeF 2 for infrared reflectivity data in both polarisations are reported for several relative orientatins of the static field H 0 and the c axis. For c along H 0 were observed the AF resonance line, its Zeeman splitting and nonreciprocal reflectivity R(-H 0 )¬=R(H 0 ). for c transverse to H 0 s and p resonances are different

Electron-energy-loss spectrum of the cuprate superconductors

We present a theoretical description of the near-specular (dipole) electron-energy-loss spectrum of a superlattice constructed from anisotropic dielectric layers, as a model of the superconducting copper-oxide-based materials. The theory is applied to a description of recent data taken on the Bi 2:2:1:2 compound. We find that parameters deduced from the electron loss spectrum are compatible with infrared reflectivity data. Manifestations of the superconducting energy gap are not evident in the new data.

A comparison of force constants, mechanical and thermal properties in Hg1−xCdxTe and Hg1−xZnxTe mixed crystals

AbstractInteratomic force constants are deduced from a fit of infrared reflectivity data of HgCdTe (MCT) and HgZnTe (MZT) mixed crystals using a basic unit model for the description of vibrational modes of low wave vector. This allows, for the first time, a direct comparison of bond strengths between MCT and MZT. The obtained results are consistent with a slight decrease in bond strength when Cd is substituted for Hg in MCT and an increase when Zn replaces Hg in MZT. These results are visualized through the bulk modulus variations with composition in both mixed crystals and are compared to known results on their thermal properties.