溅射功率对Ge2Sb2Te5薄膜光学常数的影响

研究了溅射功率对Ｇｅ２Ｓｂ２Ｔｅ５薄膜的光学常数与波长关系的影响。结果表明,在波长小于５００ｎｍ的情况下,随溅射功率的增加非晶态薄膜的折射率ｎ先增加然后减小,消光系数ｋ则逐渐减小;在波长大于５００ｎｍ的情况下,随溅射功率的增加折射率ｎ逐渐减少,消光系数ｋ先减小后增加。对于晶态薄膜样品,在整个波长范围折射率ｎ随溅射功率的增加减小后增加,消光系数ｋ则逐渐减少。薄膜样品的光学常数,在长波长范围随波长变化较大,在短波长范围变化较小。讨论了溅射功率对Ｇｅ２Ｓｂ２Ｔｅ５薄膜的光学常数影响的机理。     

溅射气压对HfO_2薄膜结构和光学性能的影响

HfO2薄膜的结构和光学性能与反应溅射时使用的气压有很强的依赖关系。薄膜的晶粒生长取向、生长速率和折射率明显受溅射气压的影响。所有的薄膜均为单斜相,晶粒尺寸在纳米量级。薄膜的折射率在1.92～2.08范围内变化,透过率大于85%。结果表明,这些HfO2薄膜很适宜用作增透膜或者高反膜。此外,通过Tauc公式推出光学带隙在5.150～5.433eV范围内变化,表明样品是良好的绝缘体。     

Fluorine-doped tin oxide films grown by pulsed direct current magnetron sputtering with an Sn target

Fluorine-doped tin oxide (FTO) films have been deposited by pulsed DC magnetron sputtering with an Sn target. Various ratios of CF4/O2 gas were injected to enhance the optical and electrical properties of the films. The extinction coefficient was lower than 1.5×10(-3) in the range from 400 to 800?nm when the CF4O2 ratio was 0.375. The resistivity of fluorine-doped SnO2 films (1.63×10(-3)?Ω?cm) deposited at 300?°C was 27.9 times smaller than that of undoped SnO2 (4.55×10(-2)?Ω?cm). Finally, an FTO film was consecutively deposited for protecting the oxidation of indium tin oxide films. The resistivity of the double-layered film was 2.68×10(-4)?Ω?cm, which increased by less than 39% at a 450?°C annealing temperature for 1?h in air.     

Reactive sputtering of SiO2-TiO2 thin film from composite Six/TiO2 targets

Coatings of SiO₂-TiO₂ films are frequently used in a number of optical thin film applications. In this work we present results from depositing films with variable Si/Ti ratios prepared by reactive sputtering. The different Si/Ti ratios were obtained by varying the target composition of composite single targets. Compared to co-sputtering this facilitates process control and composition uniformity of the films. Varying the oxygen supply during sputter deposition can result in films ranging from metallic/substoichiometric to stoichiometric oxides. Transmittance spectra of the different films are presented and the optical constants are determined from these spectra. Furthermore, the deposition process, films structure and composition of the films are discussed. The study shows that by choosing the right composition and working in the proper oxygen flow range, it is possible to tune the refractive index.     

A method for the determination of the optical constants ( n and k ) of thin films with large optical inhomogeneities

The existing methods for determining the optical constants of inhomogeneous thin films deal with non-absorbing films or at the most with films that have very small absorption (k?<?0.02). In this work, a method is presented for the determination of the optical constants of inhomogeneous thin films with large optical inhomogeneities. The optical constants are derived from normal-incidence measurements of reflectance and transmittance. The refractive index was modelled by quadratic variation. However, the absorption index was replaced by its mean value. The accuracy of this assumption was tested and its range of validity was determined. Subsequently, the method was applied to the determination of the optical constants of cerium oxide thin films.     

Effect of vacuum annealing on the phase composition of In/SnO/Si, In/SnO2/Si, and Sn/In2O3/Si heterostructures

The chemical interaction between indium and thin SnO and SnO₂ films and between tin and thin In₂O₃ films during vacuum annealing was studied. The metallic films were deposited onto single-crystal silicon substrates by magnetron sputtering, the SnO and SnO₂ films were produced by heat-treating the Sn film in flowing oxygen at 673 and 873 K, respectively, and the In₂O₃ film was produced by heat-treating the In film at 573 K. The results indicate that annealing of the In/SnO/Si and In/SnO₂/Si heterostructures in vacuum (residual pressure of 0.33 × 10^?2 Pa) at 773 K gives rise to the reduction of Sn and oxidation of In, whereas annealing of Sn/In₂O₃/Si causes partial tin substitution for indium in the cubic indium oxide lattice.     

Modeling the optical properties of tin oxide thin films

Searching the many papers reporting on the optical characteristics of tin oxide thin films, an obvious question arises: what is the origin of the very large differences in the reported optical and electrical properties of these films? The objective of the present work is to resolve this question by applying a modeling approach, simulating the refractive index of SnO, SnO₂, SnO + SnO₂, and porous tin oxide films in the visible range of the spectrum under various structure and composition conditions. Using the semi-empirical model of Wemple and DiDomenico for the dielectric function below the interband absorption edge of ionic and covalent solids, and the effective-medium theory of Bruggeman, the refractive indices of SnO, SnO₂, several mixtures of SnO and SnO₂ and various porous tin oxide films were calculated. The resulting data are compared with some published data to suggest the compositional and structural characteristics of the reported oxides. The correlation between the optical properties of the studied thin films and film composition is also indicated. It is proposed that the large spread in reported optical data is possibly a spread in the composition of the samples.     

Linear and nonlinear optical properties of RF sputtered (Pb,La)(Zr,Ti)O<Subscript>3</Subscript> ferroelectric thin films

Linear and nonlinear optical properties of (Pb,La)(Zr,Ti)O₃ (PLZT) ferroelectric thin films were presented in this paper. The PLZT ferroelectric thin films have been in situ grown on quartz substrates by radio-frequency (RF) magnetron sputtering at 650 °C. Their crystalline structure and surface morphologies were examined by X-ray diffraction and atomic force microscopy, respectively. It can be found that the PLZT thin films exhibit well-crystallized perovskite structure and good surface morphology. The fundamental optical constants (the band gap energy, linear refractive index, and linear absorption coefficient) were obtained through the optical transmittance measurements. A Z-scan technique was used to investigate the optical nonlinearity of the PLZT thin films on quartz substrates. The films display the strong third-order nonlinear optical effect. A large and negative nonlinear refractive index n ₂ is determined to be 1.21 × 10⁻⁶ esu for the PLZT thin films. All results show that the PLZT ferroelectric thin films have potential applications in optical limiting, switching, and modulated-type optical devices.     

Effect of zinc content on the refractive index of Co-sputtered Zn-doped ITO films

In this study, we investigated the possibility of using Zn-doped ITO film as an alternative material for conventional SiO2 waveguides used in optical communication. The Zn-doped ITO films were deposited on quartz substrates using a combinatorial sputtering system, which yielded composition spread Zn-In-Sn-O (ZITO) films by co-sputtering two targets of ITO and ZnO. The Zn-doped ITO films deposited at room temperature exhibited an amorphous phase in the Zn content [Zn/(Zn+In+Sn)] range of 39-54 at%. The Zn-doped ITO films deposited at low oxygen partial pressure showed resistivity below 10(-3) ohms cm and optical transmittance of approximately 85% at 550 nm. The refractive index calculated by the Swanepoel method was found to be dependent on the Zn content in the Zn-doped ITO films. The calculated bending loss from the refractive index indicated that Zn-doped ITO could be utilized as a new waveguide material for various optical devices, such as optical splitters, wavelength division multiplexers (WDMs), optical modulators, and optical switches.     

Microstructural and optoelectronic properties of rf magnetron sputtered ZnO:(Ga,Ti) semiconductor thin films

Applying radio-frequency (rf) magnetron sputtering technique, Ga–Ti co-doped ZnO [ZnO:(Ga,Ti)] transparent conductive oxide films were deposited onto glass substrates. The films were characterized by X-ray diffraction, four-point probe and UV–visible spectrophotometer. The influence of sputtering pressure on microstructure and optoelectronic properties of the films was investigated. The results show that all the films are polycrystalline with a hexagonal wurtzite structure and grow preferentially in the (002) direction. The ZnO:(Ga,Ti) films deposited at sputtering pressure of 0.4 Pa exhibit the maximum grain size of 86.6 nm, the highest transmittance of 85.9 %, the lowest resistivity of 1.67 × 10^?3 Ω cm, and the highest figure of merit of 1.38 × 10^?2 Ω^?1. The optical constants such as refractive index, extinction coefficient, dielectric constant and dissipation factor were determined using the method of whole optical spectrum fitting. Meanwhile, the dispersion behaviour of the films was studied by the single electronic oscillator model. The oscillator parameters and optical energy gaps were achieved. The results demonstrate that the microstructure and optoelectronic properties of the films are closely related to the sputtering pressure.     

P-type SnO thin films prepared by reactive sputtering at high deposition rates

SnO is an ideally suitable p-type conductive material, with large hole mobility, and has attracted great interest in connection with next-generation electronic applications. In the present work, tin oxide (SnO_x) thin films were deposited on unheated soda lime glass substrates by reactive DC sputtering from a pure Sn target. The structural, optical and electrical properties of the films were analysed as a function of the oxygen partial pressure in the sputtering atmosphere and of the post-deposition annealing temperature in air. A structural analysis was carried out using Raman spectroscopy and X-ray diffraction. Optical and electrical characterizations were performed using photo-spectrometry and Hall effect measurements, respectively. The films grown at room temperature and low oxygen pressures reached high deposition rates of above 45 nm/min, showing poorly crystalline SnO and low transparency. Subsequent heating to 350 °C allowed to achieve a more crystalline tetragonal SnO with an average visible transmittance of 65%, a p-type conductivity of 0.8 S/cm, and a hole mobility of 3.5 cm²/(V s).     

The effect of the deposition method on the optical properties of SiO2 thin films

Three films of SiO₂ deposited by three different methods (chemical vapor deposition, electron beam evaporation and r.f. sputtering) were studied to show the effect of the method of preparation on the optical constants of the films. Of the three studied films, the film prepared by electron beam gun deposition showed refractive index values (n) close to the bulk material in the spectral range 300–850 nm. No values for the absorption constant (k) were determined except for the film prepared by r.f. sputtering, which showed higher k values due to the non-stoichiometric structure of the film.     

Influence of annealing on the optical properties of 5,10,15,20-tetraphenyl-21H, 23H-porphine iron (III) chloride thin films

Optical constants (refractive index, n, and absorption index, k) of the as-deposited and annealed films of 5,10,15,20-tetraphenyl-21H, 23H-porphine iron (III) chloride (FeTPPCl) have been obtained in the wavelength range 190–2500 nm by using spectrophotometric measurements. The obtained optical constants were used to estimate the type of transition for the as-deposited and annealed films. We present a single oscillator model that describes the dispersion of refractive index. Drude model of free carriers absorption have been described for the analysis the dispersion of refractive index dispersion before and after annealing.     

Optical constants of sputter-deposited ti-ce oxide and zr-ce oxide films

Films of Ti oxide, Zr oxide, Ce oxide, Ti-Ce oxide, and Zr-Ce oxide were made by means of reactive dc magnetron sputtering in a multitarget arrangement. The films were characterized by x-ray diffraction and electrochemical measurements, both techniques being firmly connected to stoichiometric information. The optical constants n and k were evalued from spectrophotometry and from variable-angle spectroscopic ellipsometry. The two analyses gave consistent results. It was found that n for the mixed-oxide films varied smoothly between the values for the pure oxides, whereas k in the band-gap range showed characteristic differences between Ti-Ce oxide and Zr-Ce oxide. It is speculated that this difference is associated with structural effects.     

Nitrogen doped p-type SnO thin films deposited via sputtering

p-Type SnO thin films were fabricated via reactive RF magnetron sputtering on borosilicate substrates with an Sn target and Ar/O₂/N₂ gas mixture. The undoped SnO thin film consisted of a polycrystalline SnO phase with a preferred (1 0 1) orientation; however, with nitrogen doping, the preferred orientation was suppressed and the grain size decreased. The electrical conductivity of the undoped SnO thin films demonstrated a relatively low p-type conductivity of 0.05 Ω⁻¹ cm⁻¹ and it was lowered slightly with nitrogen doping to 0.039 Ω⁻¹ cm⁻¹. The results of the X-ray photoelectron spectroscopy suggested that the nitrogen doping created donor defects in the SnO thin films causing lower electrical conductivity. Lastly, both the undoped and doped SnO thin films had poor optical transmittance in the visible range.     

Determination of optical constants of thin films and multilayer stacks by use of concurrent reflectance, transmittance, and ellipsometric measurements

Using measurements of reflectance, transmittance, and the ellipsometric parameter D, we have determined the thickness, refractive index, and the absorption coefficient of various thin films and thin-film stacks. (D, the relative phase between the p- and s-polarized components, is measured for both reflected and transmitted light.) These optical measurements are performed with a specially designed system at the fixed wavelength of lambda = 633 nm over the 10 degrees -75 degrees range of angles of incidence. The examined samples, prepared by means of sputtering on fused-silica substrates, consist of monolayers and trilayers of various materials of differing thickness and optical constants. These samples, which are representative of the media of rewritable phase-change optical disks, include a dielectric mixture of ZnS and SiO(2), an amorphous film of the Ge(2)Sb(2.3)Te(5) alloy, and an aluminum chromium alloy film. To avoid complications arising from reflection and transmission losses at the air-substrate interface, the samples are immersed in an index-matching fluid that eliminates the contributions of the substrate to reflected and transmitted light. A computer program estimates the unknown parameters of the film(s) by matching the experimental data to theoretically calculated values. Although our system can be used for measurements over a broad range of wavelengths, we describe only the results obtained at lambda = 633 nm.     

Synthesis and properties of zirconia thin films

Thin films of zirconia have been synthesized using reactive DC magnetron sputtering. It has been found that films with good optical constants, high refractive index (1·9 at 600 nm) and low extinction coefficient can be prepared at ambient temperatures. The optical constants and band gap and hence the composition are dependent on the deposition parameters such as target power, rate of deposition and oxygen background pressure. Thermal annealing of the films revealed that the films showed optical and crystalline inhomogeneity and also large variations in optical constants.     

Structural and spectroscopic ellipsometry characterization for electrodeposited ZnO growth at different hydrogen peroxide concentration

This work deals with textural and optical characterization of zinc oxide (ZnO) layers obtained by potentiostatic electroplating at various hydrogen peroxide concentrations (from 0 up to 5 mM). The electrodeposition process was studied by cyclic voltametry and chronoamperometry. The [002] preferred growth orientation of hexagonal phase is obtained for the lowest hydrogen peroxide concentration (1 mM), while additionally X-ray diffraction peaks are observed for hydrogen peroxide concentration ranging from 3 to 5 mM. The optical constants and the thickness of films were determined by spectroscopic ellipsometry measurements. The refractive index of all thin films shows normal dispersion behavior. It was also found that refractive index values decrease with increasing hydrogen peroxide concentration. Further, it was revealed that the changes in the optical properties are correlated to the changes in the surface structure.     

Effect of the pressure of sputtering atmosphere on the physical properties of amorphous aluminum oxide films

Amorphous aluminum oxide films were prepared by rf-sputtering at various values of the pressure of sputtering atmosphere, and their density, refractive index, Young's modulus and internal stress were measured. The physical properties of the present films depended on the pressure of sputtering atmosphere. The density, refractive index, and Young's modulus decreased with the pressure below about 6.5 Pa, beyond which they increased. The compressive stress and tensile stress were induced in the films depending upon the pressure of sputtering atmosphere, and the tensile stress reached a maximum at the pressure of 6.5 Pa and then decreased as the pressure increased. From the results of the energy-dispersive X-ray analysis (EDX), it was found that the pressure of sputtering atmosphere gave a large influence to the chemical composition (the atomic ratio, O/Al) of the film. The pressure dependence of the physical properties was successful to be explained by the change of chemical compositions of the films. The presence of OH group in the films was verified by using FT-IR, and their microstructure was investigated by SEM study.     

Substrate bias voltage influenced structural, electrical and optical properties of dc magnetron sputtered Ta2O5 films

Tantalum oxide (Ta₂O₅) films were formed on silicon (111) and quartz substrates by dc reactive magnetron sputtering of tantalum target in the presence of oxygen and argon gases mixture. The influence of substrate bias voltage on the chemical binding configuration, structural, electrical and optical properties was investigated. The unbiased films were amorphous in nature. As the substrate bias voltage increased to −50 V the films were transformed into polycrystalline. Further increase of substrate bias voltage to −200 V the crystallinity of the films increased. Electrical characteristics of Al/Ta₂O₅/Si structured films deposited at different substrate bias voltages in the range from 0 to −200 V were studied. The substrate bias voltage reduced the leakage current density and increased the dielectric constant. The optical transmittance of the films increased with the increase of substrate bias voltage. The unbiased films showed an optical band gap of 4.44 eV and the refractive index of 1.89. When the substrate bias voltage increased to −200 V the optical band gap and refractive index increased to 4.50 eV and 2.14, respectively due to the improvement in the crystallinity and packing density of the films. The crystallization due to the applied voltage was attributed to the interaction of the positive ions in plasma with the growing film.