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Abstract Ellipsometry is an optical technique for determining properties of laminar reflecting (or transmitting) structures from the measurement of light polarization state change resulting from the light-sample interaction. In all but the simplest of cases, the measurements must be followed by data processing in which the measured data is compared to an appropriate mathematical model of the sample derived from Maxwell's equations and measurement conditions. Thus a key common problem is determining how many and which measurements to make. A single measurement in standard ellipsometry consists of one complex data point and in generalized ellipsometry, three complex data points and therefore usually more than one measurement is required. Previously we have addressed these problems using Complex Analysis in the n-k plane for homogeneous isotropic films. One of the key findings was that certain angles and wavelengths are useful and others are not. The purpose of the work here is to extend that analysis to anisotropic films. These films have a greater number of unknowns and consequently may require more measurements. The central question remains, how many measurements are needed and which specific measurements will provide sufficiently independent equations considering the unknowns. It can be that additional measurements vary to such a small degree that they are not useful considering measurement error tolerance. The work to be presented will show how to identify useful measurements based upon the anticipated, non-depolarizing sample configuration. The approach avoids making unnecessary measurements which can actually reduce the solution accuracy. Highlights • Ellipsometry solutions for anisotropic media. • High sensitivity angle-wavelength combinations. • A Priori selection of ellipsometer measurements. • Ellipsometer data analysis methods. [ABSTRACT FROM AUTHOR]

Abstract: Antimony-doped tin oxide (SnO2:Sb) thin films were fabricated by an ultrasonic spray pyrolysis method. The effect of antimony doping on the structural, electrical and optical properties of tin oxide thin films were investigated. Tin(II) chloride dehydrate (SnCl2·2H2O) and antimony(III) chloride (SbCl3) were used as a host and a dopant precursor. X-ray diffraction analysis showed that the non-doped SnO2 thin film had a preferred (211) orientation, but as the Sb-doping concentration increased, a preferred (200) orientation was observed. Scanning electron microscopy studies indicated that the polyhedron-like grains observed for the non-doped SnO2 thin films became rounder and decreased in size with the Sb-doping concentration. The lowest resistivity (about 8.4×10−4 Ω·cm) was obtained for the 3 at.% Sb-doped films. Antimony-doping led to an increase in the carrier concentration and a decrease in Hall mobility. The transmittance level in the near infrared region was lowered with the Sb-doping concentration. [Copyright &y& Elsevier]

In this paper, an extensive study of the photocurrent amplification mechanism of silicon bulk-barrier diodes (BBDs) is presented, based on simulation and experimental results. As a result of this study an analytical model is proposed. The proposed model extends previously published models and includes analytical expressions for all significant quantities of the device optoelectronic behaviour. Such quantities are barrier lowering, photocurrent, quantum efficiency and response speed as functions of the applied voltage, incident light power, light wavelength and modulation frequency, as well as a function of technological parameters. Simulation and experimental results verify the validity of the proposed analytical model, and they show that BBDs are majority carrier photodetectors with high internal photocurrent gain. Compared with common photodetectors, BBDs exhibit a very high sensitivity in the blue region of the visible spectrum. [Copyright &y& Elsevier]

The deposition and characterization of hydrogenated amorphous carbon films (a-C:H) obtained by radio-frequency plasma enhanced chemical vapor deposition on silicon and on polycarbonate are reported. Small amounts of N2 and O2 were added to a CH4–He gas mixture in order to promote the doping of the films. A systematic study of the coating structure and optical and mechanical properties as a function of gas phase composition and applied radio-frequency power is also reported. X-ray photoelectron spectroscopy (XPS) was used to quantify the amount of nitrogen and oxygen incorporation, while the characterization of sp2 carbon bonding was performed by Raman spectroscopy. Ellipsometry and UV–Vis–NIR transmission measurements were exploited to relate the refractive index and absorption of light in the visible region to the film composition and the deposition process parameters. The associated variation of the coating hardness was checked by nanoindentation measurements. The results obtained show that oxygen incorporation allows the achievement of an increased film transparency in the visible spectral range, while nitrogen dilution of the methane precursor in the plasma is responsible for the deposition of films that have a higher absorbance in the visible, due to an increased size of graphitic domains. The addition of both doping elements in a small percentage allows the preservation of the characteristic high hardness of a-C:H coatings. [Copyright &y& Elsevier]

The color variation in zirconium and titanium nitrides was investigated with respect to the atomic ratio between nitrogen and transition metals and with oxygen as the contaminant. The nitride thin films were deposited using cathodic arc evaporation. The stoichiometry of the films was varied through changes in nitrogen gas flow rate and total pressure in the deposition chamber. Thickness of all nitride films was controlled at 0.5 μm. Oxygen content in the thin films was correlated to their color. The reflectivity spectra of ZrN and TiN thin films were measured in the visible region of the spectrum and their color was quantified in the L*a*b* color system. Increasing the atomic ratio of nitrogen to transition metals causes the overall reflectivity of the gold-like color to decrease and the yellowness to increase. A change of the stoichiometry without a noticeable change of thin film color is wider for TiN than ZrN. The variation in oxygen contents results in the color change in the same direction as that of the variation of nitrogen content. Therefore, oxygen found in the nitride thin films behaves as nitrogen; it consumes free electrons from transition metal. [Copyright &y& Elsevier]

Thin film coatings of Tl4S3 or Tl2S of 100–750 nm in thickness have been deposited from a mixture of citratothallium complex and thiourea solutions at 35 or 50°C by chemical bath deposition on glass substrates coated with a thin ZnS film. Upon heating in a nitrogen atmosphere at 300°C, all the films, irrespective of the initial composition, convert to crystalline Tl2S. The variation of the optical absorption coefficient with photon energy for a typical sample of Tl2S suggests forbidden direct transition as the mechanism for optical excitation. All the films, ‘as prepared’ as well as those heated to 300°C, are photoconductive. In the heated films dark conductivity is typically 7.5×10−6 Ω−1 cm−1 and photoconductivity, 5×10−5 Ω−1 cm−1. [Copyright &y& Elsevier]

Combined solid state phase diagram studies and physical property measurements of the various n-type transparent conducting oxide (TCO) phases in the CdO-In2O3-SnO2 system have been carried out. The 1175 °C (air) subsolidus phase diagram has been established, including solid solution limits for binary and ternary compositions. From these limits and electrical property measurements vs. doping and degree of reduction, the prevailing defect mechanisms can be deduced. In addition to intrinsic (native) defects (e.g. oxygen vacancies) and extrinsic donor-doping of the end member compounds (e.g. SnIn⋅ in In2O3), ternary solid solutions exhibit both isovalent doping (e.g. [Cd′In]=[SnIn⋅] in bixbyite, spinel) and donor-to-acceptor imbalance (e.g. [SnIn⋅]>[Cd′In] in bixbyite, spinel). Aliovalent doping can also lead to the formation of point defect associates, as in Sn-doped In2O3 (ITO), as confirmed by combined Rietveld analyses of X-ray and neutron diffraction data. Cation exchange between sublattices in the spinel phase plays an important role in determining phase stability and band structure. The physical properties of the TCO phases in the CdO-In2O3-SnO2 system are presented for both bulk ceramics and thin films. [Copyright &y& Elsevier]

We investigate InxCd1−xO materials, where x=0.0, 0.031, 0.063 and 0.125, to understand their high electrical conductivity and optical transparency windows, using the full-potential linearized augmented plane wave (FLAPW) method. In addition, we employ the screened exchange LDA (sX-LDA) method to evaluate accurate band structures including band gap that is underestimated by the LDA calculations. The results show a dramatic Burstein–Moss shift of the absorption edge by the In doping, reflecting the small effective mass of the Cd 5s conduction band. The calculated direct band gaps, 2.36 eV for x=0.0 and 3.17 eV for x=0.063, show excellent agreement with experiment. The effective mass of the conduction band of CdO is calculated to be 0.24 me (in the ▵ direction), in good agreement with an experimental value of 0.27me, explaining its high electrical conductivity. The hybridization between the Cd 5s and the In 5s states yields complex many-body effects in the conduction bands: a hybridization gap in the conduction bands and a band-gap narrowing which cancels the further Burstein–Moss shift for higher In doping. [Copyright &y& Elsevier]

We review data on transparent and electrically conducting films of ITO (i.e. In2O3:Sn). A survey is given on the most recent progress, in 2001, of fundamental electronic bandstructure, techniques to boost the conductivity, and alternative dopants and manufacturing techniques. We then outline quantitative theories for the optical properties and their applications. Finally, we consider ITO films for uses in optimized electrochromic window coatings capable of yielding indoor comfort and energy efficiency. [Copyright &y& Elsevier]

The optical properties of titanylphthalocyanine (TiOPc) thin film fabricated by physical jet deposition technique were investigated by using absorption, femtosecond (fs) optical Kerr effect (OKE) and fs pump–probe techniques. The third-order nonlinear optical susceptibility of TiOPc film was measured to be 3×10−10 esu. The OKE response of TiOPc films shows a decay process with subpicosecond time constant, demonstrating that the excited state of TiOPc molecule has little contribution to the photo-induced birefringence. From the fs pump–probe experiment, a complicated decay behavior with three decay components was observed, which originates from the contribution of exciton–exciton annihilation process, the enhanced intersystem crossing process and the relaxation of the triplet state. [Copyright &y& Elsevier]

(Pb0.9La0.1)TiO3 thin films were deposited onto indium tin oxide-coated glass and Pt/Ti/SiO2/Si substrates by spin coating. One set of the solutions was sonication-treated during the sol preparation, while the other remained untreated for comparison. The results were analyzed in terms of perovskite developments, dielectric constants and losses, polarization behavior, and optical properties. Perovskite formation temperatures became lower by application of the sonication process. Furthermore, dielectric/ferroelectric and optical transmittance properties were improved substantially. [Copyright &y& Elsevier]

Holmium oxide films were prepared by an electron beam deposition method in vacuum. Films exhibited b.c.c. type structure of holmium sesquioxide as determined from electron diffraction studies. Optical properties of Ho2O3 films deposited onto quartz substrates were examined for the wavelength range of 0.2–2.5 μm. Films are characterized by a high transparency between 0.3 and 2.5 μm. The complex refractive index, n*=n−jk, and the complex dielectric function, &epsiv;*=&epsiv;′−j&epsiv;′′, for optical frequencies were evaluated. The dispersion characteristics for n(λ), k(λ), &epsiv;′(ω) and &epsiv;′′(ω) were presented. At λ=0.55 μm the refractive index was n=1.80. Ho2O3 films exhibited low absorption in the whole visible spectral range (k<0.002). The high frequency relative permittivity of Ho2O3 was also determined: &epsiv;′∞=3.24. [Copyright &y& Elsevier]

Thin films of vanadium dioxide (VO2) on glass substrates were produced by sputtering and two different sol–gel methods. The sputtering method used carefully controlled deposition rates from a vanadium metal target in an argon/oxygen atmosphere to ensure correct stoichiometry. The alkoxide sol was based on a vanadium triisopropoxy oxide precursor; the substrates were dip coated in a dry atmosphere and reduced by vacuum heat treatment. The aqueous sol was made by pouring molten vanadium pentoxide (V2O5) directly into distilled water. After dip coating the substrates were reduced by heat treatment in a low pressure carbon monoxide and carbon dioxide (CO/CO2) atmosphere. The electrical and optical properties of these films were then tested, and are presented here for comparison. All three methods produced films that switch well (as indicated by the conductivity measurements) with the aqueous technique giving the largest magnitude transition. The change in reflectance between the semiconductor and metallic states is similar for the alkoxide and sputtered samples, but smaller for the thicker film produced by the aqueous route. The aqueous sol–gel technique is easier and cheaper than the alkoxide method as expensive precursors and the need to coat in a dry atmosphere are eliminated, although a reducing gas mixture is necessary to reduce the films successfully. [Copyright &y& Elsevier]

This work involves a comparative study of nanocrystalline titanium and indium oxides as well as TiO2–In2O3 composites prepared by a sol–gel method from concentrated hydrous titanium dioxide and indium hydroxide sols. Highly transparent uniform films were fabricated from the sols by a spin-coating technique. TiO2–In2O3 nanocomposites possess pronounced extreme dependencies of both the apparent bandgap and the refractive index on the film composition. No chemical interaction between the oxides was observed during annealing to temperatures between 200 and 700 °C. This behavior was attributed to the effect of surface states formed at the nanocrystallite interfaces. Other possible causes of the pronounced dependence of the optical and electronic properties on the TiO2-to-In2O3 ratio are also discussed. Abrupt changes in resistivity, photoresistivity and photocurrent decay time of the composite films were observed for composites where the TiO2 content ranged from 25 to 50 wt.% and are associated with the formation of a three-dimensional infinite cluster of interconnected In2O3 nanoparticles. [Copyright &y& Elsevier]

TiO2 thin films were spin-coated on Si (100) substrates via an aqueous sol–gel route using Ti(OBun)4 and H2O2 as starting materials, and were annealed in air at different temperatures up to 550 °C for 1 h. X-Ray diffractometry indicates that crystallization into anatase started at 350 °C. The 350 °C-annealed films were further characterized by Auger electron spectroscopy, X-ray photoelectron spectroscopy, and variable angle spectroscopic ellipsometry. The results show that homogeneous, carbon-free TiO2 films with high refractive index (n=2.3 at 550 nm) were successfully obtained under an annealing temperature as low as 350 °C. The indirect and direct optical absorption bandgaps of the anatase film are estimated as 3.23 and 3.80 eV, respectively. [Copyright &y& Elsevier]

Vanadium pentoxide thin films were successfully fabricated on indium–tin–oxide-coated glasses by r.f. sputtering in an Ar/O2 gas mixture. The films gave excellent cyclic voltammograms with a two-step electrochromism, yellow to green, and then green to blue. The effect of the Li+ concentration in the electrolyte on the voltammogram cycles was also studied. The thin films were characterized before and after coloration by X-ray diffraction. No significant changes in the crystallographic structure occurred after coloration. The optical properties of films colored at three different potentials were measured in the UV-vis near infra-red (NIR) wavelength range. The results showed that the changes in the optical absorption are consistent with the color changes of the films. In particular, when the potential increased the optical absorption decreased in the wavelength range 500–900 nm, and the optical absorption edge shifted towards lower energies. The optical density of each colored film was monitored continuously when the circuit was opened after coloration for 15 min. The green, yellow and blue colors were relatively stable for several tens of hours. [Copyright &y& Elsevier]