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Nitrogen-doped TiO2 films exhibit good photocatalytic ability in the visible (VIS) light region. This study reports the fabrication of these films using arc ion plating (AIP) in different ratios of nitrogen partial pressure (PN2) to oxygen partial pressure (PO2) without substrate heating and/or applied bias. This approach allows a significant broadening of the range of possible substrates to be used. X-ray diffraction (XRD) patterns indicate that these films deposited at room temperature are amorphous, and surface electron microscope (SEM) and atomic force microscope (AFM) images show that they have rough surfaces. Their transmittance and optical properties are measured with a spectrometer and ellipsometer, respectively. In addition, the bandgap energies of these amorphous films are derived by the ellipsometer from the Tauc–Lorentz (TL) model. The results indicate that the N-doped TiO2 film with a PN2/PO2 ratio of 1/4 attains the narrowest bandgap and the highest absorbance in the visible region. It can be attributed to the prominent Ti–N peaks observed in the sample's Ti and N X-ray photoelectron spectroscopy (XPS) spectra. In addition, verified with the methylene blue (MB) test, this sample exhibits the best photocatalytic performance for its narrowest energy gap. [ABSTRACT FROM AUTHOR]

The Tauc–Lorentz–Urbach (TLU) dispersion model allows us to build a dielectric function from only a few parameters. However, this dielectric function is non-analytic and presents some mathematical drawbacks. As a consequence of this issue, the model becomes inaccurate. In the present work, we will adopt a procedure to conveniently transform the TLU model into a self-consistent dispersion model. The transformation involves the integration of the original TLU imaginary dielectric function ϵ 2 by using a Lorentzian-type function of semi-width, Γ. This novel model is analytic and obeys the other necessary mathematical requirements of the optical constants of solid-state materials. The main difference with the non-analytic TLU model occurs at values of the photon energy near or lower than that of the bandgap energy (within the Urbach absorption region). In particular, this new model allows us to reliably extend the optical characterization of amorphous-semiconductor thin films within the limit to zero photon energy. To the best of our knowledge, this is the first time that the analytic TLU model has been successfully used to accurately determine the optical constants of unhydrogenated a-Si films using only their normal-incidence transmission spectra. [ABSTRACT FROM AUTHOR]

In the UV-visible-near infrared regions from 245 to 1000 nm, variable-angle spectroscopic ellipsometer (VASE) was used to investigate optical functions of As2S3 and As2Se3 thin films. In the entire measured spectral range, data were analyzed by assembly from several dispersion models. These assemblies comprise individual Tauc–Lorentz supplemented by several Lorentz (TL-group) or single Cody–Lorentz with several Lorentz (CL-group) models. For As2S3 and As2Se3 thin films, the optical parameters were quantified. The model parameters, such as the Lorentz amplitude, resonance frequency, oscillator width, extinction coefficients, refractive indices, and Urbach and optical band energy of both films were obtained. The band gap energy Eg was experimentally determined using the obtained data of CL-group from (αhν)1/2 vs. hν plots. It is found that the band gap energies of As2Se3 and As2S3 were 1.796 and 2.349 eV, respectively. The Eg values for the films were theoretically investigated by the bond statistics of the random covalent network model (CRNM) with the aid of Manca's relation. Plausible agreement between the experimental and calculated Eg values for both samples was obtained. [ABSTRACT FROM AUTHOR]

Although Polyaniline (PAni) has been largely studied during several decades, many of its features are still not completely understood. Its optical properties have been widely characterized by simple techniques such as absorbance, transmittance, or reflectance in UV–vis–NIR spectral range, but mathematical model describing its optical properties is still scarce. In this study, spectroscopic ellipsometry was utilized to provide spectral data of PAni thin films. We develop a method for film thickness estimation by analysis of interference pattern and we show a very good-quality fitting to measured data with Tauc–Lorentz model in the spectral range 200–1600 nm. [ABSTRACT FROM AUTHOR]

In this study, indium–zinc oxide (IZO) films of different compositions were deposited on quartz glass by alternate sputtering of ZnO:Al and In 2 O 3 :Sn targets at room temperature. Spectroscopic ellipsometry (SE) measurements were carried out over the wavelength range 193–1690 nm in order to estimate the chemical, optical, and electrical properties of the IZO films using various dispersion models, i.e., the Tauc–Lorentz (TL), and Lorentz, Gaussian, and Drude models. The experimental results showed that the tail absorption was essentially affected by the Zn content and crystallinity of the film. The optical constants of the amorphous IZO films were accurately estimated using the TL and Drude models, and inclusion of the Lorentz model in the SE analysis overcame the inhomogeneity effect caused by preferential orientation growth. On the basis of these results, a k factor was defined and used to estimate the Zn contents of the IZO films. The variations in the k factors as a function of Zn content agreed well with those of the band gaps of the IZO films. Furthermore, for films with better conductivities, the resistivity values obtained using the SE and Hall methods were similar, but low carrier concentrations caused failure of the Drude model. [ABSTRACT FROM AUTHOR]

The temperature dependence of solar cells is a fundamental problem determines the device performance at unstable operating and environmental conditions. In this paper considering the temperature dependence of practical parameters, we have used an analytical drift-diffusion model to calculate the characteristic parameters of solar cell. We applied the Modified Tauc-lorentz temperature dependent model to describe the dielectric function of active layer, in order to study the performance of an organic P3HT: PCBM solar cell at different temperatures. Solving the steady-state continuity equation for electrons and holes regarding the dissociation probability of Onsager Braun along with bimolecular recombination rate, we have calculated the carrier's concentration in P3HT: PCBM organic active layer. The absorption coefficient and its temperature dependence is compared with the results of similar experimental data. [ABSTRACT FROM AUTHOR]

The effect of Helium (He) dilution on optical and photoelectric properties of hydrogenated amorphous silicon (a-Si:H) thin film samples prepared at substrate temperature of 75°C with increased growth rate by plasma-enhanced chemical vapor deposition (PECVD) technique is studied using spectrophotometric (SP) and steady-state photocarrier grating techniques (SSPG). The values of refractive index, absorption coefficient, thickness and optical energy gap, which are found from the analysis of transmission spectra using Swanepoel method, are compared with those obtained by employing variable-angle spectroscopic ellipsometry technique. The samples exhibit a tendency towards an increase in energy gap and a decrease in refractive index with the increase in He dilution. The obtained optical absorption coefficients of a-Si:H samples are compared with those of hydrogenated microcrystalline silicon ( μc-Si:H) and crystalline silicon (c-Si) samples. It is also found that the change in He dilution has an influence on the ambipolar diffusion length, minority and majority mobility-lifetime products. [ABSTRACT FROM AUTHOR]

Abstract: The optical properties of boron- and phosphorus-doped polycrystalline silicon films with light (~1×1016 cm−3), moderate (~5×1017 cm−3) and heavy doping (~1×1019 cm−3) were investigated in this work. The films were prepared by solid-phase crystallization of evaporated amorphous silicon films on borosilicate glass. Tauc–Lorentz models with one or two oscillators were used to model both reflection and transmission data collected by a spectrophotometer over the wavelength range of 400nm–2000nm. The results indicate that the crystal quality of the films is improved by phosphorus doping, while boron has a negligible impact on the crystal quality. The poly-Si films exhibit greater absorption than c-Si for visible wavelengths. This enhanced absorption is believed to be associated with defected a-Si material at the grain boundaries and intra-grain defects. [ABSTRACT FROM AUTHOR]

Several, nearly-1-µ m -thick, pure, unhydrogenated amorphous-silicon (a-Si) thin layers were grown at high rates by non-equilibrium rf-magnetron Ar-plasma sputtering (RFMS) onto room-temperature low-cost glass substrates. A new approach is employed for the optical characterization of the thin-layer samples, which is based on some new formulae for the normal-incidence transmission of such a samples and on the adoption of the inverse-synthesis method, by using a devised Matlab GUI environment. The so-far existing limiting value of the thickness-non-uniformity parameter, Δ d , when optically characterizing wedge-shaped layers, has been suppressed with the introduction of the appropriate corrections in the expression of transmittance. The optical responses of the H-free RFMS-a-Si thin films investigated, were successfully parameterized using a single, Kramers–Krönig (KK)-consistent, Tauc–Lorentz oscillator model, with the inclusion in the model of the Urbach tail (TLUC), in the present case of non-hydrogenated a-Si films. We have also employed the Wemple–DiDomenico (WDD) single-oscillator model to calculate the two WDD dispersion parameters, dispersion energy, E d , and oscillator energy, E so . The amorphous-to-crystalline mass-density ratio in the expression for E d suggested by Wemple and DiDomenico is the key factor in understanding the refractive index behavior of the a-Si layers under study. The value of the porosity for the specific rf-magnetron sputtering deposition conditions employed in this work, with an Ar-pressure of ~4.4 Pa, is found to be approximately 21%. Additionally, it must be concluded that the adopted TLUC parameterization is highly accurate for the evaluation of the UV/visible/NIR transmittance measurements, on the H-free a-Si investigated. Finally, the performed experiments are needed to have more confidence of quick and accurate optical-characterizations techniques, in order to find new applications of a-Si layers in optics and optoelectronics. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the sol–gel spin-coating method has been used to make – thin films. These films have been prepared in various composition ratios to observe changes in their optical and structural properties. Reflectance and transmittance spectra were collected in the spectral range of 300–1000nm and were accurately fit using the Tauc–Lorentz model. Film thicknesses, refractive indices, absorption coefficients, and optical band gaps were extracted from the theoretical fit. The highest refractive index value was found at 5% doping. The structure of the films was characterized by X-ray diffractometry and Fourier transform infrared spectrometry, while the surface morphology was examined through atomic force microscopy. [Copyright &y& Elsevier]

Abstract: Amorphous carbon nitride (CN x ) films were prepared by KrF excimer laser ablation of a graphite target in a nitrogen atmosphere in the inverse PLD geometry. From the ellipsometric point of view, the challenging properties of these films were their exponentially decaying thickness as a function of distance from the ablation source, accompanied by a laterally varying chemical composition and structure. Optical models were developed to accurately describe the dependence of film properties on distance from the ablation, layer thickness, and nitrogen pressure. Multi-layer models were used to characterize the surface roughness as well as lateral inhomogeneities. Multiple angles of incidence and multiple wavelengths were applied in the ranges of 66–72° and 250–1000nm, respectively. A microspot capability of the spectroscopic ellipsometer (with a spot size of about 100μm) was exploited to decrease the error caused by the lateral inhomogeneity within the measurement spot. Material properties were derived using the empirical Cauchy dispersion model as well as the Tauc–Lorentz parametric dielectric function model. These models allowed the quantitative determination of the band gap and the oscillator parameters in addition to the layer thicknesses and dielectric functions. [Copyright &y& Elsevier]

Spectroscopic ellipsometry, scanning electron microscopy, and transmission electron microscopy are all invaluable routine characterization techniques to determine the thickness of silicon nitrides during manufacturing of compound semiconductor devices. We describe in detail the accuracy and convenience of each technique. In addition to thickness, nitride composition is another process parameter that needs to be controlled in manufacturing. Therefore, we also discuss using UV Raman spectroscopy, Rutherford backscattering spectroscopy, and spectroscopic ellipsometry to measure composition. Finally, we discuss the correlation between electrical parameters (capacitance and breakdown voltage) and the stoichiometry of the silicon nitride used as a dielectric in a metal-insulator-metal capacitor. [Copyright &y& Elsevier]

In this work, we study the influence of the geometry of a thin film on its transmission spectrum, as measured on amorphous As-based chalcogenide layers grown onto 1-mm-thick soda-lime-silica glass substrates. A new method is suggested for a comprehensive optical characterization of the film-on-substrate specimen, which is based upon some novel formulae for the normal-incidence transmittance of such a specimen. It has to be emphasized that they are not limited to the usual cases, where the refractive index, n, of the film and that of the thick transparent substrate, s, must obey: n 2 > > k 2 and s 2 > > k 2 , respectively, where k stands for the extinction coefficient of the semiconductor. New expressions for the top and bottom envelopes of the transmission spectrum are also obtained. The geometry limitation usually found when characterizing strongly-wedge-shaped films, has been eliminated with the introduction of an appropriate parameter into the corresponding equations. The presence of crossover points in the top and bottom envelopes of the transmission spectrum, for these strongly-wedge-shaped chalcogenide samples, has been both theoretically predicted and experimentally confirmed. [ABSTRACT FROM AUTHOR]

Accurate reference dielectric functions play an important role in the research and development of optical materials. Libraries of such data are required in many applications in which amorphous semiconductors are gaining increasing interest, such as in integrated optics, optoelectronics or photovoltaics. The preparation of materials of high optical quality in a reproducible way is crucial in device fabrication. In this work, amorphous Ge (a-Ge) was created in single-crystalline Ge by ion implantation. It was shown that high optical density is available when implanting low-mass Al ions using a dual-energy approach. The optical properties were measured by multiple angle of incidence spectroscopic ellipsometry identifying the Cody-Lorentz dispersion model as the most suitable, that was capable of describing the dielectric function by a few parameters in the wavelength range from 210 to 1690 nm. The results of the optical measurements were consistent with the high material quality revealed by complementary Rutherford backscattering spectrometry and cross-sectional electron microscopy measurements, including the agreement of the layer thickness within experimental uncertainty. [ABSTRACT FROM AUTHOR]

Nitrogen-doped TiO2 films were prepared by reactive ion-beam sputtering deposition (IBSD) in a mixed atmosphere of NH3 and O2 at a substrate temperature of 400 °C. X-ray photoelectron spectra revealed the presence of six ions, i.e., N3−, N2−, N1−, N+, N2+, and N3+, respectively, in the films. The amorphous films had complex, randomly oriented chemical bonds. The Tauc–Lorentz model was employed to determine the bandgap energy of the amorphous films prepared using different NH3/O2 gas mixing ratios by ellipsometry. In addition, the optical constants of the films were measured. With the increase in the NH3/O2 gas mixture ratio to 3.0, the bandgap of N-doped TiO2 narrowed to ~2.54 eV. [ABSTRACT FROM AUTHOR]