Self-consistent optical constants of sputter-deposited B₄C thin films

The optical constants of ion-beam-sputtered B?C films have been measured by ellipsometry in the 190-950 nm range. The set of data has been extended toward both shorter and longer wavelengths with data in the literature, along with interpolations and extrapolations, in order to obtain a self-consistent set of data by means of Kramers-Kr?nig analysis. All data correspond to films that were deposited by sputtering on nonheated substrates, and hence they are expected to be amorphous. The B?C bandgap was calculated as a fitting parameter of Tauc equations for indirect transitions using the present optical constants. Good global accuracy of the data was estimated through the use of various sum rules. The consistent data set includes the visible to the extreme UV (EUV); this large spectrum of characterization will enable the design of multilayer coatings that combine a relatively high reflectance in parts of the EUV with a desired performance at a secondary range, such as the visible.     

Reflectance measurements and optical constants in the extreme ultraviolet for thin films of ion-beam-deposited SiC, Mo, Mg2Si, and InSb and of evaporated Cr

Reflectance measurements and optical constants of thin films of ion-beam-deposited SiC, Mo, Mg(2)Si, and InSb and of evaporated Cr have been measured in the extreme-ultraviolet (EUV) spectral region from 49.0 to 200.0 nm. In this spectral region no optical constant data were available for materials deposited by ion-beam deposition. We compared our data with those for bulk samples and for thin films prepared by different techniques. The goal of this research has been to study candidate materials for multilayer coatings in the EUV.     

Experimental comparison of extreme-ultraviolet multilayers for solar physics

We compare the reflectance and stability of multilayers comprising either Si/Mo, Si/Mo2C, Si/B4C, Si/C, or Si/SiC bilayers, designed for use as extreme-ultraviolet (EUV) reflective coatings. The films were deposited by using magnetron sputtering and characterized by both x-ray and EUV reflectometry. We find that the new Si/SiC multilayer offers the greatest spectral selectivity at the longer wavelengths, as well as the greatest thermal stability. We also describe the optimization of multilayers designed for the Solar-B EIS instrument. Finally, we compare experimental reflectance data with calculations and conclude that currently available optical constants cannot be used to adequately model the performance of many of these multilayers.     

Influence of filament-to-substrate distance on the spectroscopic,structural and optical properties of silicon carbide thin films deposited by HWCVD technique

Silicon carbide (SiC) thin films were deposited using hot wire chemical vapor deposition (HWCVD) technique from pure silane and methane gas mixture. The effect of filament distance to the substrate on the structural and optical properties of the films was investigated. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), Raman scattering spectroscopy and UV–Vis–NIR spectroscopy were carried out to characterize SiC films. XRD patterns of the films indicated that the film deposited under highest filament-to-substrate distance were amorphous in structure, while the decrease in distance led to formation and subsequent enhancement of crystallinity. The Si–C bond density in the film structure obtained from FTIR data, showed significant increment with transition from amorphous to nano-crystalline structure. However, it remained almost unchanged with further improvement in crystalline volume fraction. From Raman data it was observed that the presence of amorphous silicon phase and sp ² bonded carbon clusters increased with the decrease in distance. This reflected in deterioration of structural order and narrowing the optical band gap of SiC films. It was found that filament-to-substrate distance is a key parameter in HWCVD system which influences on the reactions kinetics as well as structural and optical properties of the deposited films.     

Transparent amorphous zinc oxide thin films for NLO applications

This review focuses on the growth and optical properties of amorphous zinc oxide (ZnO) thin films. A high quality ZnO films fabricated by dip-coating (sol–gel) method were grown on quartz and glass substrates at temperature equal to 350 K. The amorphous nature of the films was verified by X-ray diffraction. Atomic Force Microscopy was used to evaluate the surface morphology of the films. The optical characteristics of amorphous thin films have been investigated in the spectral range 190–1100 nm. Measurement of the polarized optical properties was shows a high transmissivity (80–99%) and low absorptivity (<5%) in the visible and near infrared regions at different angles of incidence. Linear optical properties were investigated by classic and Time-Resolved Photoluminescence (TRPL) measurements. Photoluminescence spectrum exhibits a strong ultraviolet emission while the visible emission is very weak. An innovative TRPL technique has enabled the measurement of the photoluminescence decay time as a function of temperature. TRPL measurements reveal a multiexponential decay behavior typical for amorphous thin films. Second and third harmonic generation measurements were performed by means of the rotational Maker fringe technique using Nd:YAG laser at 1064 nm in picosecond regime for investigations of the nonlinear optical properties. The obtained values of second and third order nonlinear susceptibilities were found to be high enough for the potential applications in the optical switching devices based on refractive index changes. Presented spectra confirm high structural and optical quality of the investigated zinc oxide thin films.     

Use of artificial neural networks to predict thickness and optical constants of thin films from reflectance data

Artificial neural networks and the Levenberg–Marquardt algorithm are combined to calculate the thickness and refractive index of thin films from spectroscopic reflectometry data. Two examples will be discussed, the first is a measurement of thickness and index of transparent films on silicon, and the second is a measurement of three thicknesses and index of poly-silicon in a rough poly-silicon on oxide stack. A neural network is a set of simple, highly interconnected processing elements imitating the activity of the brain, which are capable of learning information presented to them. Reflectometry has been used by the semiconductor industry to measure thin film thickness for decades. Modeling the optical constants of a film in the visible region with a Cauchy dispersion model allows the determination of both thickness and refractive index of most transparent thin films from reflectance data. The use of an alloy interpolation model for the optical constants of poly-silicon allows the determination of thicknesses and poly optical constants. In this work artificial neural networks are used to obtain good initial estimates for thickness and dispersion model parameters, these estimates are then used as the starting point for the Levenberg–Marquardt algorithm which converges to the final solution in a few iterations. These measurement programs were implemented on a Nanometrics NanoSpec 8000XSE.     

脉冲磁控溅射制备硼掺杂氧化锌纳米薄膜的光学特性研究

采用脉冲磁控溅射法制备硼掺杂氧化锌（ZnO：B）纳米薄膜,研究了其结构和光学特性,经XRD分析,ZnO：B为多晶纳米薄膜,具有六方钎锌矿结构,薄膜沿着c轴取向择优生长。薄膜在可见光和近红外光谱区的透光性很好,其中在可见光区的平均透光率可达84％以上,而在近红外区的透光率随着波长增加而逐渐降低至45％。在可见光区,ZnO：B纳米薄膜的光学常数随波长的变化很小且数值基本趋于恒定,而在紫外区,光学常数随波长的变化很明显,并且在367nm和397nm附近存在两个紫外发光峰。     

Improved method for determination of optical constants of organic thin films from reflection and transmission measurements

A new technique for determining the optical properties of organic thin films is presented. A detailed evaluation of the accuracy of the determined optical constants has been performed, and the best combination of measured values yielding the smallest errors in the index of refraction for realistic experimental uncertainties has been found. The proposed method utilizes the fact that optical constants are smooth continuous functions, which reduces the possibility of encountering multiple solutions. The method consists of two steps. In the first step the optical constants at all wavelengths and the film thickness are determined. In the second step the thickness and the imaginary part of the index of refraction are kept fixed while we reevaluate the real part of the index of refraction by using a different objective function with improved sensitivity to the refractive index. After verifying that the proposed method is capable of an accurate estimation of optical constants, we determine the index of refraction data of vanadyl-phthalocyanine in the visible spectral range.     

Structural, electrical and optical characterization of N- and P-type SiC:H films deposited using ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance chemical vapour deposition (ECR-CVD) method from a mixture of methane, silane and hydrogen, and using diborane and phosphine as doping gases. The effects of changes in the diborane and phosphine levels on the optical bandgap and conductivity were investigated. In the case of boron-doped films, there is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were largely amorphous and the bandgap decreases as the diborane levels are highly conductive and contains the whereas films deposited at a high microwave power of 800 W at low diborane levels are highly conductive and contains the silicon microcrystalline phase. These films become amorphous as the diborane level is increased, while the optical bandgap remains relatively unaffected throughout the entire range of diborane levels investigated. In the case of phosphorus-doped films, Raman scattering analysis showed that the deposition conditions strongly influence the structural, optical and electrical properties of the SiC:H films. Unlike boron doping, doping with phosphorus can have the effect of increasing the silicon microcrystalline phase in the SiC:H films which were prepared at low (150 W) and high (600 W) microwave powers. Films prepared at high microwave power showed only small variations in the optical bandgap, suggesting that good phosphorus doping efficiency can be achieved in films which contain the silicon microcrystalline phase (mc-SiC:H).     

Optical constants and Drude analysis of sputtered zirconium nitride films

Opaque and semitransparent dc magnetron-sputtered ZrN films on glass and silicon have been optically characterized with spectral reflectance measurements and ellipsometry. High rate sputtered ZrN has good optical selectivity, i.e., higher than 90% infrared reflectance and a pronounced reflectance step in the visible to a reflectance minimum of less than 10% at 350 nm. The results are comparable with those obtained for single crystalline samples and those prepared by chemical vapor deposition. The complex optical constant (N = n v ik) for opaque films has been determined in the 0.23-25-μm wavelength range with Kramers-Kronig integration of bulk reflectance combined with oblique incidence reflectance for p-polarized light. A variable angle of incidence spectroscopic ellipsometer has been used for determination of the optical constants in the 0.28-1.0-μm wavelength region. The results of the two methods show excellent agreement. The results indicate that ZrN is free electronlike and the Drude model can be applied. The best opaque films had Drude plasma energies (?ω(p) between 6.6 and 7.5 eV and relaxation energies (?/τ) between 0.29 and 0.36 eV. Ellipsometer data for the semitransparent films show that the refractive index (n) in the visible increases with decreasing film thickness whereas the extinction coefficient (k) is essentially unchanged. The optical properties are improved by deposition upon a heated substrate.     

GaGeTe films as phase-change optical recording media

Ga₂₀Ge₃₀Te₅₀ thin films deposited by vacuum evaporation on various substrates have been studied for their structural and optical properties. The as-deposited amorphous films were crystallized by thermally annealing them. The optical constants of the amorphous films indicate semiconducting behaviour (n> k). The optical bandgap (E_g) determined from Tauc's plot is 0.7 eV. The change in reflectance on crystallization has been utilized to obtain maximum optical contrast by optimising the thickness of the film.     

Growth and optical properties of ZnIn2Se4 films

Thin films of ZnIn₂Se₄ were deposited on quartz substrates at 297 K by the conventional thermal evaporation technique. The as-deposited films were amorphous. On annealing at 623 K under vacuum for 3 h, the films crystallized with a preferred (1 1 2) orientation corresponding to the chalcopyrite-type structure. Films deposited on a quartz substrate heated to 573 K were also crystalline. The optical constants were computed from the measured transmittance and reflectance at normal incidence of light in the wavelength range 400 to 2000 nm. The analysis of the data gave a direct gap of 2.2 and 2.06 eV for the amorphous and crystallized films, respectively. The dispersion curve exhibited a peak above the absorption edge. An indirect gap of 1.8 eV for the crystallized films and a direct forbidden gap of 1.75 eV for the amorphous films were also deduced. A direct allowed transition with a gap of 2.065 eV and an indirect transition with a gap of 1.69 eV were deduced for the crystalline films deposited on the heated substrate.     

Optical constants and band edge of amorphous zinc oxide thin films

The optical characteristics of amorphous zinc oxide (a-ZnO) thin films grown by radio frequency reactive magnetron sputtering on various substrates at temperature < 325 K have been investigated in the spectral range 340-1600 nm. The amorphous nature of the a-ZnO films was verified by X-ray diffraction and the optical constants were obtained by analysis of the measured ellipsometric spectra using the Cauchy-Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.67-1.93 and 3.9 × 10^− 8-0.32, respectively. The band edge of the films on Si (100) and quartz has been determined by spectroscopic ellipsometry (3.39 ± 0.05 eV) and spectrophotometric (3.35 ± 0.05 eV) methods, respectively. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 60.5°. Measurement of the polarized optical properties shows a high transmissivity (81%-99%) and low absorptivity (< 5%) in the visible and near infrared regions at different angles of incidence. Also, we found that there was a higher absorptivity for wavelength < 370 nm. This wavelength, ∼ 370 nm, therefore indicated that the band edge for a-ZnO thin films is about 3.35 eV.     

化学水浴法制备ZnS薄膜光学性能

利用薄膜分析系统测量不同沉积时间制备的ZnS薄膜透射谱,通过分析薄膜透射谱,来确定ZnS薄膜光学常数和禁带宽度.实验结果表明,在线性生长阶段,薄膜的沉积速率大约为1 nm/min,具有很好的线性关系,沉积0.5 h的ZnS薄膜在可见光范围内光透过率为82%左右.     

Thermal and optical properties of Ge5Bi18Se77 films

Amorphous films of Ge₅Bi₁₈Se₇₇ deposited by vacuum evaporation have been studied for their thermal and optical properties. Differential scanning calorimetry (DSC) has been used to perform the thermal analysis to estimate the activation energy for crystallization (E_c) and the order of crystallization (m) of this material. The high value of (E_c), 1.672 eV, indicates good stability of the amorphous phase. The optical constants of the as-deposited, amorphous and the thermally annealed crystalline films indicate semiconducting behavior and the band gap (E_g) determined from Tauc's plot are 0.92 eV and 0.8 eV for the amorphous and crystalline films, respectively. The value of the absorption coefficient () is of the order of 10⁴cm^-1 in the optical range for both amorphous and crystalline films. The studies on optical and thermal properties confirm the suitability of these firms in phase change optical recording.     

Study of optical properties and light induced effects on Inq3 thin film used in organic light emitting devices

In this report, the optical properties of tris-(8-hydroxyquinoline) metal complex Inq₃; used as light-emitting layer in electroluminescent (EL) devices are shown. The material has been synthesized and the thin films have been deposited by thermal evaporation on quartz and silicon substrates. The optical constants (n and k) of Inq₃ thin films have been determined using spectroscopic ellipsometry. Light induced effects on optical properties of films have been studied using ellipsometry, photoluminescence and UV–visible transmission measurements. Enhanced photoluminescence intensity with shift in peak position as well as modification in optical constants on light exposure in vacuum indicates phase transformation in Inq₃ films.     

Structural and optical properties of high quality ZnO thin film on Si with SiC buffer layer

ZnO thin films are grown on Si substrates with SiC buffer layer using ion plasma high frequency magnetron sputtering. These substrates are fabricated using a technique of solid phase epitaxy. With this technique SiC layer of thickness 20-200 nm had been grown on Si substrates consisting pores of sizes 0.5-5 μm at SiC and Si interface. Due to mismatching in lattice constants as well as thermal expansion coefficients, elastic stresses have been developed in ZnO film. Pores at the interface of SiC and Si are acting as the elastic stress reliever of the ZnO films making them strain free epitaxial. ZnO film grown on this especially fabricated Si substrate with SiC buffer layer exhibits excellent crystalline quality as characterized using X-ray diffraction. Surface topography of the film has been characterized using Atomic Force Microscopy as well as Scanning Electron Microscopy. Chemical compositions of the films have been analyzed using Energy Dispersive X-ray Spectroscopy. Optical properties of the films are investigated using Photoluminescence Spectroscopy which also shows good optical quality.     

Amorphous Films of Ternary Zinc and Tin Oxides for Transparent Electronics

Amorphous films of two varieties of zinc stannate (ZnSnO₃ and Zn₂SnO₄) have been considered that were fabricated by radio-frequency sputtering of ceramic compound targets containing ZnO and SnO₂ in 1: 1 and 2: 1 ratios. The elemental and phase compositions of the films and their optical and electrical parameters were determined. The transparency of the films in the visible spectral range is on average 87%. Zinc stannate amorphous films have a high electrical conductivity in contrast to amorphous ZnO and SnO₂. This phenomenon, which makes it possible to use zinc stannate amorphous films in transparent and flexible electronics, is explained.     

Study of surface topography and optical properties of Ge15Bi38Se47 films

Adherent and smooth amorphous GeBiSe films deposited by vacuum evaporation at substrate temperatures less than 30 °C have been studied for their structural and optical properties. The films were crystallized by thermal annealing and they were found to be polycrystalline in nature. A correlation between X-ray diffraction (XRD) data and surface topography is reported. Optical constants calculated from reflectance and transmittance data indicate semiconducting behaviour. The optical band gap of the as-deposited film is 1.0 eV. The measured optical contrast at 0.8 m is 44%. No significant changes in the optical parameters have been observed after exposing the samples to laboratory ambient for a period of six months. © 1998 Chapman & Hall     

Determination of the Optical Constants of Solids in the Visible by Dispersive Fourier Transform Spectroscopy: 1. Reflection Measurements on an Opaque Solid

Abstract

A Michelson interferometer has been developed for determining the optical constants of solids in the visible and ultraviolet by dispersive Fourier transform spectroscopy. Systematic phase errors in amplitude reflection spectroscopy arising from factors such as non-flatness and imperfect alignment of the specimen are discussed in detail, and it is shown that they can be eliminated by following a simple measuring procedure. The performance of the instrument is demonstrated with measurements in the visible region of the optical constants of thin films of Cu and Au, vacuum deposited on optically polished fused quartz substrates.