High Frequency Dielectric Constant Research Articles

Optical properties of Sulfur doped InP single crystals

Optical properties of InP:S single crystals were investigated using spectrophotometric measurements in the spectral range of 200–2500 nm. The absorption coefficient and refractive index were calculated. It was found that InP:S crystals exhibit allowed and forbidden direct transitions with energy gaps of 1.578 and 1.528 eV, respectively. Analysis of the refractive index in the normal dispersion region was discussed in terms of the single oscillator model. Some optical dispersion parameters namely: the dispersion energy (Ed), single oscillator energy (Eos), high frequency dielectric constant (ε∞), and lattice dielectric constant (εL) were determined. The volume and the surface energy loss functions (VELF & SELF) were estimated. Also, the real and imaginary parts of the complex conductivity were calculated.

Annealing effect on structural and optical properties of Se87.5Te10Sn2.5 thin films

Thin films of Se87.5Te10Sn2.5 were prepared by vacuum thermal evaporation technique. Various optical constants were calculated for the studied composition. The mechanism of the optical absorption follows the rule of direct transition. It was found that the optical energy gap (Eg) decreases from 2.26 to 1.79eV with increasing the annealing temperature from 340 to 450K. This result can be interpreted by the Davis and Mott model. On the other hand, the maximum value of the refractive index (n) is shifted towards the long wavelength by increasing the annealing temperature. In addition, the high frequency dielectric constant (εL) increased from 31.26 to 48.11 whereas the ratio of the free carriers concentration to its effective of mass N/m⁎ decreased from 4.3 to 2.09 (×1057(m−3Kg−1)). The influence of annealed temperature on the structure was studied by using the X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD studies show that the as-deposited films are amorphous in nature, but the crystallinity improved with increasing the annealing temperature. Furthermore the particle size and crystallinity increased whereas the dislocation and strains decreased with increasing the annealing temperature. SEM examination showed that the annealing temperature induced changes in the morphology of the as-deposited film.

Effect of Nano ZnO on the Optical Properties of Poly(vinyl chloride) Films

Optical properties of pure and doped poly(vinyl chloride) (PVC) films, prepared by using casting technique, with different nanosize zinc oxide (ZnO) concentrations (1–20) wt% have been studied. Parameters such as extinction coefficient, refractive index, real and imaginary parts, Urbach energy, optical conductivity, infinitely high frequency dielectric constant, and average refractive index were studied by using the absorbance and transmittance measurement from computerized UV-visible spectrophotometer (Shimadzu UV-1601 PC) in the spectral range 200–800 nm. This study reveals that the optical properties of PVC are affected by the doping of ZnO where the absorption increases and transmission decreases as ZnO concentration increases. The extinction coefficient, refractive index, real and imaginary parts, infinitely high frequency dielectric constant, and average refractive index values were found to increase with increasing impurity percentage. The Urbach energy values are found to be decreasing with increasing ZnO concentration. The optical conductivity increased with photon energy after being doped and with the increase of ZnO concentration.

Spectroscopic ellipsometry analysis of perovskite manganite films for resistance switching devices

Pr0.5Ca0.5MnO3 (PCMO) films were deposited on LaAlO3 (100) substrates changing process pressure from 1.33 to 5.33Pa by RF magnetron sputtering. Current–voltage characteristic measurements and spectroscopic ellipsometry measurements were carried out to investigate the mechanism of resistance switching in PCMO films. Resistance switching was observed in the devices composed of the PCMO films deposited at low pressures of 1.33 and 2.67Pa. The deposition pressure dependence of the electronic structure of PCMO films was detected as a difference in dielectric functions by spectroscopic ellipsometry. Spectroscopic ellipsometry data indicated that the PCMO films exhibiting resistance switching had large oscillator strength of the electric dipole charge transition in (MnO6)9− and (MnO6)8− octahedral complexes, small oscillator strength of d–d transitions in Mn3+ and Mn4+ ions, and large high frequency dielectric constant. The formation of (MnO6)9− and (MnO6)8− octahedral complexes and oxygen vacancies might be required for obtaining large resistance switching.

Impact of dielectric parameters on the reflectivity of 3C–SiC wafers with a rough surface morphology in the reststrahlen region

A layer-on-substrate model is used to obtain the infrared reflectance for 3C–SiC with a rough surface morphology. The effect of varying dielectric parameters of the “damaged layer” on the observed reflectivity of the 3C–SiC in the reststrahlen region is assessed. Different simulated reflectance spectra are obtained to those if the dielectric parameters of the “substrate” were varied. Most notable changes in the shape of the simulated reststrahlen peak are observed for changes in the high frequency dielectric constant, the phonon damping constant, the phonon frequencies and “thickness” of damaged surface layer.

Dielectric response of Fe2O3 crystals and thin films

We report the static (ε0) and high frequency (ε∞) dielectric constants of haematite (α-Fe2O3) as calculated using density functional perturbation theory. The values for bulk iron oxide are ε011=26.41; ε033=17.84; ε∞11=7.87 and ε∞33=7.57. The effective static dielectric screening of porous thin-films is predicted in aqueous solutions, using effective medium theory, to range between 33 and 44 depending on the crystal packing density. The large spread in literature values (12–120) can only be explained through surface and micro-structuring effects. These results will be important for interpreting and modelling the materials behaviour, particularly in electrochemical and photoelectrochemical cells.

Refractive Index Dispersion and Analysis of the Optical Parameters of (PMMA/PVA) Thin Film

The optical characteristics of (PMMA/PVA) thin films are investigated by spectrometric measurements. Sample with different percentage are prepared with constant thickness (110 m) using casting technique. The real (n) and imaginary (k) parts of refractive index and dielectric constant of the thin films are determined. Some important parameters of optical absorption, such as the oscillator energy (E0), dispersion energy (Ed), the average value of oscillator strength (S0), wavelength (0) of single oscillator and the ratio carrier concentration to the effective mass (N/m*) have been evaluated. The values obtained for the high frequency dielectric constant through two procedures are in the range of (6.31-7.35) for all ranges of the different concentrations.

Electronic and optical properties of InAs1-xPx alloys under the effect of temperature and pressure

The calculations are based on local empirical pseudo-potential method (EPM) coupled with the virtual crystal approximation (VCA) which incorporates compositional disorder as an effective potential. This work is concerned with the dependence of the electronic energy band structures for InAs1-xPx alloys on temperature and pressure. Some physical quantities such as band gaps, bowing parameters, refractive indices, and high frequency dielectric constants of the considered alloys with different phosphide concentration were calculated and their variations with the temperature and hydrostatic were studied. There is a good agreement between our results and the available experimental data for the binary compounds which may be a support for the results of the ternary alloys.

Optical dispersion parameters based on single-oscillator model and optical absorption of nanocrystalline metal phthalocyanine films: A comparison study

Nanocrystalline thin films of {Co(II), Cu(II), Mn(III), Pb(II) and Zn(II)} phthalocyanine complexes were deposited by spin coating sol–gel technique. The surface morphologies of the films are found to be dependable on the type of the metal complex. The absorption spectra of the films show two well defined absorption bands of phthalocyanine molecule; namely Soret (B-band) and Q-bands. The Q-band absorption of the phthalocyanine complexes shifts to longer wavelength with the central metal change. The analysis of the spectral behavior of the absorption coefficient (α) in the absorption region revealed two expected indirect transitions. The refractive index (n) and the absorption index (k) were calculated using the measured data of the transmittance T(λ) and reflectance R(λ) coefficients. The dispersion parameters such as dispersion energy (Ed), oscillator energy (Eo), high frequency dielectric constant (ε∞), and lattice dielectric constant (εL) were determined using the single oscillator model. The main reason for the change in dispersion parameters of the phthalocyanine complexes may be attributed to the intensity of the metal coordination bonds that are dependent on the bound metal atoms due to their electronegativity change. The founded results of the nano-crystalline metal phthalocyanine thin films can be useful for optoelectronic applications. Discussion of the obtained results and their comparisons with the available published literature were also considered.

Dielectric properties of Ge2Sb2Te5 phase-change films

The static (εs) and high-frequency (ε∞) dielectric constants of amorphous and NaCl-type crystalline Ge2Sb2Te5 were measured and the relaxation effects in films were studied using impedance spectroscopy. On the basis of a simple method that allows obtaining the dielectric constant in the low resistivity planar structure, static and high frequency dielectric constants and their temperature dependencies were calculated in both phases. A surprising value of εs ≈ 750 in crystalline films was obtained, but the effective dielectric constant, εeff, estimated from the Maxwell-Wagner effective medium model, is significantly lower (εeff ≈ 34.9). Such a high value of εs obtained by electrical impedance measurements has been explained by Maxwell-Wagner relaxation, the separation of charges at the interface between grains and grain boundaries. Additionally, three relaxation processes (alpha, beta, and Ohmic relaxation) were observed in the amorphous phase and four relaxations (dipolar relaxation of grains, Ohmic relaxation of grains, dipolar relaxation of grain boundaries, and Maxwell-Wagner relaxation) were observed in the crystalline phase. From these results, a new rule for the selection of materials for optical phase-change data storage is proposed: polycrystalline films must have a high volume fraction of grain boundaries. This requirement increases the effective dielectric constant and the reflectance contrast between amorphous and crystalline phases.

Comparable optical properties and dispersion parameters of monomeric axial ruthenium phthalocyanine thin films

The ruthenium phthalocyanine complex [(n-hexyl)8PcRu] (2) and their derivatives [(n-hexyl)8PcRu(t-buNC)2] (3) and [(n-hexyl)8PcRu(Mepyr)2] (4) have been synthesized and characterized. The optical properties of their films have been studied by spectrophotometer measurements of transmittance and reflectance at normal incidence of light in the spectral range of 200–2500nm. Absorption spectra of the films showed B and C absorption bands in the UV region followed by a Q-band in the visible region. The absorption parameters such as molar extinction coefficient, oscillator strength and electric dipole strength have been reported. The type of electronic transition is determined from an analysis of the absorption coefficient and found to be indirect allowed transition with onset energy gap and optical energy gap. The single oscillator model has been applied to calculate the dispersion parameters. The oscillator energy, the dispersion energy, the high frequency dielectric constant, the lattice dielectric constant and the ratio of free charge carriers concentration to their effective mass were evaluated. The dielectric properties of the films were also determined, showing that peripheral and axial ligand substituents on the complexes have a significant effect on their surface coverage.

Optical characteristics of Tl0.995Cu0.005InS2 single crystals

Optical properties of Tl0.995Cu0.005InS2 single crystals were studied using transmittance and reflectance measurements in the spectral wavelength range of 300–2500nm. The optical constants (n and k) were calculated at room temperature. The analysis of the spectral behavior of the absorption coefficient in the absorption region revealed indirect transition. The refractive index dispersion data were analyzed in terms of the single oscillator model. Dispersion parameters such as the single oscillator energy (Eo), the dispersion energy (Ed), the high frequency dielectric constant (ε∞), the lattice dielectric constant (εL) and the ratio of free charge carrier concentration to the effective mass (N/m⁎) were estimated. The third order nonlinear susceptibility (χ(3)) was calculated according to the generalized Miller's rule. Also, the real and imaginary parts of the complex dielectric constant were determined.

The response of temperature and hydrostatic pressure of zinc-blende GaxIn1−xAs semiconducting alloys

The electronic band structure of GaxIn1−xAs alloy is calculated by using the local empirical pseudo-potential method including the effective disorder potential in the virtual crystal approximation. The compositional effect of the electronic energy band structure of this alloy is studied with composition x ranging from 0 to 1. Various physical quantities such as band gaps, bowing parameters, refractive indices, and high frequency dielectric constants of the considered alloys with different Ga concentrations are calculated. The effects of both temperature and hydrostatic pressure on the calculated quantities are studied. The obtained results are found to be in good agreement with the available experimental and published data.

Optical parameters of ZnTe determined using continuous-wave terahertz radiation

The optical parameters of three ZnTe crystal wafers of different thicknesses were determined using transmittance measurements of continuous-wave terahertz radiation from a two-color photomixing source. The parameters are extracted by fitting the transmittance data with theoretical curves generated using a Drude-Lorentz dielectric model of the crystal and a bootstrap statistical analysis of the fits. It was found at room temperature that the low and high frequency dielectric constants are ϵ(0)=9.8±0.2 and ϵ(∞)=7.3±0.6, respectively. The transverse optical phonon frequency was found to be νTO=6.0±1.3 THz. Sample specific properties such as the plasma, collision, and phonon damping frequencies were determined and used for an approximate calculation of carrier concentration. The results are compared with a comprehensive review of earlier values from the literature. Our results are consistent with previous work, falling within the spread of accepted values, and demonstrate that this method is particularly suited for determining the low and high frequency dielectric constants of semiconductor samples.

Zinc concentration effect on structural, optical and electrical properties of Cd1−xZnxSe thin films

Cd1−xZnxSe thin films with different compositions (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) were deposited on glass substrates using successive ionic layer adsorption and reaction (SILAR) method at room temperature and ambient pressure. The zinc concentration (x) effect on the structural, morphological, optical and electrical properties of Cd1−xZnxSe thin films were investigated. The X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies showed that all the films exhibited polycrystalline nature and were covered well on glass substrates. The energy dispersive X-ray (EDAX) analysis confirmed nearly stoichiometric deposition of the films. The energy bandgap values were changed from 1.99 to 2.82eV depending on the zinc concentration. Bowing parameter was calculated as 0.08eV. The electron effective mass (me*/mo), refractive index (n), optical static and high frequency dielectric constants (ɛo, ɛ∞) values were calculated by using the energy bandgap values as a function of the zinc concentration. The resistivity values of the films changed between 105 and 107Ωcm with increasing zinc concentration at room temperature.

Characteristics of SnO2 thin films prepared by SILAR

SnO2 thin films were deposited on glass substrates by using Successive Ionic Layer Adsorption and Reaction (SILAR) method at room temperature. The film thickness effect on characteristic parameters such as structural, morphological, optical and electrical properties of the films was studied. Also, the films were annealed in oxygen atmosphere (400 °C, 30 min) and characteristic parameters of the films were investigated. The X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) studies showed that all the films exhibited polycrystalline nature with tetragonal structure and were covered well on glass substrates. After the investigation of the crystalline and surface properties of the films, it was found that they were improving with increasing film thickness. Optical band gap decreased from 3.90 eV to 3.54 eV and electrical conductivity changed between 0.015–0.815 (Ω-cm)−1as the film thickness increased from 215 to 490 nm. The refractive index (n), optical static and high frequency dielectric constants (ɛo, ɛ∞) values were calculated by using the optical band gap values as a function of the film thickness.

Optical absorption and dispersion analysis based on single-oscillator model of polypyrrole (PPy) thin film

In this work, polypyrrole samples were synthesized by chemical oxidative polymerization technique with Iron (III) chloride as an oxidant. Thin films of PPy were prepared by spin coating technique. The molecular structure of polypyrrole film was characterized by Fourier transform infrared spectroscopy (FTIR). The optical properties of the PPy films were studied using spectrophotometric measurements of the transmittance and reflectance at normal incidence of light in the wavelength range from 200 to 2500nm. The recorded absorption measurements in the UV–vis region show two well defined absorption bands. The analysis of the spectral behavior of the absorption coefficient (α), in the absorption region revealed two direct transitions. The dispersion parameters were determined and discussed based on the single oscillator model. According to the analysis of dispersion curves, the parameters, namely; dispersion energy (Ed), oscillator energy (Eo), high frequency dielectric constant (ɛ∞) and lattice dielectric constant (ɛL) were evaluated. Discussion of the obtained results and their comparison with the previous published data were also given.

A first-principles molecular dynamics approach for predicting optical phonon lifetimes and far-infrared reflectance of polar materials

The Lorentz oscillator model is well-known for its effectiveness to describe the far-infrared optical properties of polar materials. The oscillator strength and damping factor in this model are usually obtained by fitting to experimental data. In this work, a method based on first-principles simulations is developed to parameterize the Lorentz oscillator model without any fitting parameters. The high frequency dielectric constant is obtained from density functional perturbation theory, while the optical phonon frequencies and damping factors are calculated using an analysis of ab initio molecular dynamics trajectories. This method is then used to predict the far-infrared properties of GaAs, and the results are in good agreement with experimental data.

Optical absorption and spectrophotometric studies on the optical constants and dielectric of poly (o-toluidine) (POT) films grown by spin coating deposition

In this work, a poly(o-toluidine) “POT” was synthesized by chemical oxidative polymerization method in aqueous media. High uniform and good adhesion thin films of POT have been successfully deposited by the spin coating technique. The films were characterized by X-ray diffraction (XRD) and Fourier transforms infrared (FTIR) spectroscopy. The XRD pattern of the POT shows the semi-crystalline nature of the films. FTIR studies show the information of functional groups in POT. The optical transmittance and reflectance of POT film was measured in the 200–2500nm wavelength range. The absorption coefficient analysis shows that the optical band gaps of POT film are direct allowed transition band gaps with 1.2 and 2.6eV. Other optical absorption parameters such as extinction molar coefficient, oscillator strength and electric dipole strength were also calculated. The dispersion parameters were determined and discussed based on the single oscillator model. According to the analysis of dispersion curves some important parameters such as dispersion energy (Ed), oscillator energy (Eo), high frequency dielectric constant (ε∞) and lattice dielectric constant (εL) were also evaluated. Discussion of the obtained results and their comparison with the previous published data were also given. The obtained desirable results of POT thin film can be useful for the optoelectronic applications.

Optical properties and the dispersion parameters of new zinc Phthalocyanine benzofuran derivative prepared by non-vacuum spin coating technique

The optical properties of 2(3),9(10),16(17),23(24)-tetrakis-{6-(-benzofuran-2-carboxylate)-hexylthio} phthalocyaninatozinc(II) {Zn[Pc(b-S(CH2)6OCOBz-furan)4], (ZnPcBzF) thin film prepared by spin coating method were investigated. The optical constants of the prepared film were determined using spectrophotometric measurements of the transmittance and reflectance at normal incidence in the spectral range 200–800nm. The analysis of the spectral behavior of the absorption coefficient in the intrinsic absorption region revealed two direct allowed optical band gap of 2.58 and 3.87eV. The dispersion of the refractive index was discussed in terms of the single oscillator using Sellmeier dispersion formula. The high frequency dielectric constant (ε∞) and the lattice dielectric constant (εL) were estimated. From the optical constants analysis, the optical conductivity was also considered. Discussion of the obtained results and their comparison with the previous published data were also given. The obtained results of this new zinc phthalocyanine benzofuran derivative (ZnPcBzF) support the desirable feature for the microelectronic and optoelectronic devices.