Dependence of film thickness on the structural and optical properties of ZnO thin films

ZnO thin films are prepared on glass substrates by pulsed filtered cathodic vacuum arc deposition (PFCVAD) at room temperature. Optical parameters such as optical transmittance, reflectance, band tail, dielectric coefficient, refractive index, energy band gap have been studied, discussed and correlated to the changes with film thickness. Kramers-Kronig and dispersion relations were employed to determine the complex refractive index and dielectric constants using reflection data in the ultraviolet-visible-near infrared regions. Films with optical transmittance above 90% in the visible range were prepared at pressure of 6.5 × 10⁻⁴ Torr. XRD analysis revealed that all films had a strong ZnO (0 0 2) peak, indicating c-axis orientation. The crystal grain size increased from 14.97 nm to 22.53 nm as the film thickness increased from 139 nm to 427 nm, however no significant change was observed in interplanar distance and crystal lattice constant. Optical energy gap decreased from 3.21 eV to 3.19 eV with increasing the thickness. The transmission in UV region decreased with the increase of film thickness. The refractive index, Urbach tail and real part of complex dielectric constant decreased as the film thickness increased. Oscillator energy of as-deposited films increased from 3.49 eV to 4.78 eV as the thickness increased.     

Optical simulation, optimized design and fabrication of (ZrO2)x-(Al2O3)1−x composite films with thin inserted TiO2 layers for ArF-line high transmission attenuated phase shift mask blank applications

The tunable optical constants of the stoichiometric (ZrO₂)_x-(Al₂O₃)_1−x composite films with thin inserted TiO₂ layers are simulated as π-phase shifters. The optimized composition range of the superlattices to be used as a high transmission attenuated phase shift mask (HT-APSM) blank is found. The absorption edge shifts to the longer wavelengths when the thickness fraction of the TiO₂ layer increases. The optimized film for ArF-line HT-APSM blank applications must have the lower inspection transmittance for the better inspection and the lower reflectance at the exposure wavelength for a better aerial image as π-phase shifters, and they will be easier to fabricate than a superlattice. In order to find such a film, (ZrO₂)_x-(Al₂O₃)_1−x composite films with various inserted TiO₂ layers are simulated. The optimal deposition processes of such a film are also determined. For example, a (ZrO₂)_0.187-(Al₂O₃)_0.813 composite film with two inserted TiO₂ thin layers is fabricated. The optical properties are as follows: a transmittance of 19.8%, a reflectance of 9.1%, a calculated phase shift of ∼181.5° at the exposure wavelength of 193 nm, and a transmittance of 18.9% at the inspection wavelength of 257 nm. Such a film should be used as an optimized HT-APSM blank.     

The optical properties of thin erbium films

The effective dielectric constant, ε′₂, of very thin films of erbium on sodium chloride substrates was determined from measurements of normal incidence reflectance and transmittance in the visible spectrum. ε′₂ showed a maximum which moved to longer wavelengths as the film thickness increased. Electron microscopy revealed that the film islands grew flatter and more irregular with thickness. The shape factor of the islands, F, was calculated by a modified Maxwell-Garnett method and became smaller as the film thickness increased.     

Structural-optical study of high-dielectric-constant oxide films

High-k polycrystalline Pr₂O₃ and amorphous LaAlO₃ oxide thin films deposited on Si(0 0 1) are studied. The microstructure is investigated using X-ray diffraction and scanning electron microscopy. Optical properties are determined in the 0.75-6.5 eV photon energy range using spectroscopic ellipsometry. The polycrystalline Pr₂O₃ films have an optical gap of 3.86 eV and a dielectric constant of 16-26, which increases with film thickness. Similarly, very thin amorphous LaAlO₃ films have the optical gap of 5.8 eV, and a dielectric constant below 14 which also increases with film thickness. The lower dielectric constant compared to crystalline material is an intrinsic characteristic of amorphous films.     

Sputter deposition of high transparent TiO2−xNx/TiO2/ZnO layers on glass for development of photocatalytic self-cleaning application

In this study, TiO_2−xN_x/TiO₂ double layers thin film was deposited on ZnO (80 nm thickness)/soda-lime glass substrate by a dc reactive magnetron sputtering. The TiO₂ film was deposited under different total gas pressures of 1 Pa, 2 Pa, and 4 Pa with constant oxygen flow rate of 0.8 sccm. Then, the deposition was continued with various nitrogen flow rates of 0.4, 0.8, and 1.2 sccm in constant total gas pressure of 4 Pa. Post annealing was performed on as-deposited films at various annealing temperatures of 400, 500, and 600 °C in air atmosphere to achieve films crystallinity. The structure and morphology of deposited films were evaluated by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and atomic force microscopy (AFM). The chemical composition of top layer doped by nitrogen was evaluated by X-ray photoelectron spectroscopy (XPS). Photocatalytic activity of samples was measured by degradation of Methylene Blue (MB) dye. The optical transmittance of the multilayer film was also measured using ultraviolet-visible light (UV-vis) spectrophotometer. The results showed that by nitrogen doping of a fraction (∼1/5) of TiO₂ film thickness, the optical transmittance of TiO_2−xN_x/TiO₂ film was compared with TiO₂ thin film. Deposited films showed also good photocatalytic and hydrophilicity activity at visible light.     

Thickness dependent optical dispersion parameters and nonlinear optical properties of nanostructured Cr doped CdO thin films

Cr doped CdO thin films were deposited on glass substrates by reactive DC magnetron sputtering with varying film thickness from 250 to 400 nm. XRD studies reveal that the films exhibit cubic structure with preferred orientation along the (2 0 0) plane. The optical transmittance of the films decreases from 92 to 72%, whereas the optical energy band gap of the films decreased from 2.88 to 2.78 eV with increasing film thickness. The Wemple–DiDomenico single oscillator model has been used to evaluate the optical dispersion parameters such as dispersion energy (E_d), oscillator energy (E_o), static refractive index (n_o) and high frequency dielectric constant (ε_∞). The nonlinear optical parameters such as optical susceptibility (χ⁽¹⁾), third order nonlinear optical susceptibility (χ⁽³⁾) and nonlinear refractive index (n₂) of the films were also determined.     

Microstructure and dielectric properties of La2O3 doped amorphous SiO2 films as gate dielectric material

As a potential gate dielectric material, the La₂O₃ doped SiO₂ (LSO, the mole ratio is about 1:5) films were fabricated on n-Si (0 0 1) substrates by using pulsed laser deposition technique. By virtue of several measurements, the microstructure and electrical properties of the LSO films were characterized. The LSO films keep the amorphous state up to a high annealing temperature of 800 °C. From HRTEM and XPS results, these La atoms of the LSO films do not react with silicon substrate to form any La-compound at interfacial layer. However, these O atoms of the LSO films diffuse from the film toward the silicon substrate so as to form a SiO₂ interfacial layer. The thickness of SiO₂ layer is only about two atomic layers. A possible explanation for interfacial reaction has been proposed. The scanning electron microscope image shows the surface of the amorphous LSO film very flat. The LSO film shows a dielectric constant of 12.8 at 1 MHz. For the LSO film with thickness of 3 nm, a small equivalent oxide thickness of 1.2 nm is obtained. The leakage current density of the LSO film is 1.54 × 10⁻⁴ A/cm² at a gate bias voltage of 1 V.     

Behaviour of transmittance and phase change on transmission with film thickness at intermediate thicknesses

The behaviour of the optical functions T (transmittance) and X_t (phase change on transmission) for an absorbing film have been investigated as the film thickness was increased from a small fraction of a wavelength up to a thick solid. When plotted against thickness, the values of T oscillated at a frequency related to the quantity, x=2πd/λ which is equal to the phase thickness divided by the refractive index. Ultimately, for real materials, the oscillations were damped to zero due to the absorption term in the complex dielectric constant of the film material. In the case of X_t, the most notable feature was the sudden phase changes of ±π which occurred repeatedly as the thickness increased and the values of x at which this occurred could be related to the conditions for constructive or destructive interference between light rays coming from the top and bottom of the film.     

异质界面对Ca(Mg1/3Nb2/3)O3/CaTiO3叠层薄膜结构和介电性能的影响

采用异质叠层方式制备出一定厚度的Ca(Mg_1/3Nb_2/3)O₃/CaTiO₃(CMN/CT)叠层薄膜,研究了异质界面对薄膜结构、微观形貌及介电性能的影响及其规律.根据实验测试结果,提出CMN/CT叠层薄膜的模拟等效电路,建立介电常数和介电损耗的理论计算公式.结果表明:CMN/CT异质叠层薄膜具有完全正交钙钛矿结构,结构致密,厚度均匀,薄膜中存在独立的CMN和CT相.异质界面处存在过渡层,随着薄膜中异质界面个数增加,介电常数增大,介电损耗减小.减小界面过渡层的厚度,有利于提高CMN/CT叠层薄膜的介电性能.     

Influence of thickness on the optical properties of vacuum-deposited a-Si:H films

The influence of the thickness of the a-Si : H film on its optical properties was studied using spectrophotometric measurements of the film transmittance and reflectance in the wavelength range 200–3000 nm. Both the refractive index and the absorption coefficient were found to increase as the film thickness increased and the absorption edge shifted to lower energies. Both the optical energy gap, E_g, and Urbach parameter values, E₀, decreased with increasing thickness. This decrease in E_g and E₀ was slow for thicknesses above 400 nm.     

Transparent conductive ITO/Ag/ITO multilayer electrodes deposited by sputtering at room temperature

ITO/Ag/ITO multilayers have been prepared onto conventional soda lime glass substrates by sputtering at room temperature. The optical and electrical characteristics of single layer and multilayer structures have been investigated as a function of the Ag and ITO film thicknesses. Transmittance and sheet resistance values are found mainly dependent on the Ag film thickness; whereas the wavelength range at which the maximum transmittance is achieved can be changed by adjusting the ITO films thickness. ITO/Ag/ITO electrodes with sheet resistance below 6 Ω/sq have been obtained for Ag film thickness above 10 nm and ITO layers thickness in the 30-50 nm range. These multilayers also show high transmittance in the visible spectral region, above 90% by discounting the glass substrate, with a maximum that is located at higher wavelengths for thicker ITO.     

Fabrication of textured SnO2:F thin films by spray pyrolysis

Transparent conductive SnO₂:F thin films with textured surfaces were fabricated on soda-lime-silica glass substrates by spray pyrolysis. Structure, morphology, optical and electrical properties of the films were investigated. Results show that the film structure, morphology, haze, transmittance and sheet resistance are dependent on the substrate temperature and film thickness. An optimal 810 nm-thick SnO₂:F film with textured surface deposited at 520 °C exhibits polycrystalline rutile tetragonal structure with a (2 0 0) orientation. The sheet resistance, average transmittance in visible region, and haze of this film were 8 Ω/□, 80.04% and 11.07%, respectively, which are suitable for the electrode used in the hydrogenated amorphous silicon solar cells.     

Influence of Au thickness on the optical and electrical properties of transparent and conducting TiO2/Au/TiO2 multilayer films

Au-intermediate TiO₂/Au/TiO₂ (TAT) multilayer films were deposited by RF magnetron sputtering onto glass substrates. Changes in the optical and electrical properties of the films were investigated with respect to the thickness of the Au interlayer.The observed optical and electrical properties were dependent on the thickness of the Au interlayer. The resistivity decreased to 3.3 × 10⁻⁴ Ω cm for TiO₂ films with a 20 nm-thick Au interlayer and the optical transmittance was also influenced by the Au interlayer. Although optical transmittance deteriorated as Au thickness increased, TiO₂ films with a 5 nm-thick Au interlayer showed a relatively high optical transmittance of 80% at a wavelength of 550 nm. In addition, since a TAT film with a 5 nm-thick Au interlayer showed a relatively high work function value, it is an alternative candidate for use as a transparent anode in OLEDs and flat panel displays.     

Sol-gel preparation and characterization of nanoporous ZnO/SiO2 coatings with broadband antireflection properties

Nanoporous ZnO/SiO₂ bilayer coatings were prepared on the surface of glass substrates via sol-gel dip-coating process. The structural, morphological and optical properties of the coatings were characterized. The refractive indices of ZnO layer and SiO₂ layer are 1.34 and 1.21 at 550 nm, respectively. The transmittance and reflectance spectra of the coatings were investigated and the broadband antireflection performance of the bilayer structure was determined over the solar spectrum. The solar transmittances in the range of 300-1200 nm and 1200-2500 nm are increased by 6.5% and 6.2%, respectively. The improvement of transmittance is attributed to the destructive interference of light reflected from interfaces between the different refractive-index layers with an optimized thickness. Such antireflection coatings of ZnO/SiO₂ provide a promising route for solar energy applications.     

Transparent conducting molybdenum-doped zinc oxide films deposited by RF magnetron sputtering

A new transparent conducting oxide (TCO) film with low resistivity and high transmittance in the visible range, molybdenum-doped zinc oxide (MZO), was successfully prepared by RF magnetron sputtering method on glass substrates at room temperature. The structural, electrical, and optical properties as a function of film thickness were investigated. All the samples have a preferred orientation with the (0 0 2) planes parallel to the substrates. The resistivity initially decreases and then shows an increase with the increase of the film thickness. When the thickness is 400 nm, the film has its best crystallinity and lowest resistivity 9.2 × 10⁻⁴ Ω cm with a Hall mobility of 30 cm² V⁻¹ s⁻¹ and a carrier concentration of 2.3 × 10²⁰ cm⁻³. The average transmittance in the visible range exceeds 84% for all thickness films.     

Elaboration of (1 1 1)-oriented La-doped PZT thin films on platinized silicon substrates

PLZT thin films with different thickness were deposited in situ on platinum coated silicon substrates using a multi-target sputtering system. The purpose was to grow (1 1 1)-textured PLZT films on Pt (1 1 1). To this aim, the role of some key parameters on both crystalline quality and electrical properties was investigated. An ultra-thin TiO₂ seeding layer was deposited, prior to PLZT, which strongly affected the crystallographic orientation of the films. The relation between temperature deposition and film crystallinity is analysed. TEM observations show the presence of some very small grains of Zr_0.9La_0.1O_1.95 at the film bottom interface. In the range of thickness investigated, the plot of the inverse capacitance as a function of the film thickness split up into two different curves, each with a linear shape, which however allows determination of a single value of interface capacitance. Above a thickness of 400-500 nm a saturation of the dielectric properties seems to be reached.     

Stabilization of a very high-k crystalline ZrO2 phase by post deposition annealing of atomic layer deposited ZrO2/La2O3 dielectrics on germanium

The impact of the ZrO₂/La₂O₃ film thickness ratio and the post deposition annealing in the temperature range between 400 °C and 600 °C on the electrical properties of ultrathin ZrO₂/La₂O₃ high-k dielectrics grown by atomic layer deposition on (1 0 0) germanium is investigated. As-deposited stacks have a relative dielectric constant of 24 which is increased to a value of 35 after annealing at 500 °C due to the stabilization of tetragonal/cubic ZrO₂ phases. This effect depends on the absolute thickness of ZrO₂ within the dielectric stack and is limited due to possible interfacial reactions at the oxide/Ge interface. We show that adequate processing leads to very high-k dielectrics with EOT values below 1 nm, leakage current densities in the range of 0.01 A/cm², and interface trap densities in the range of 2-5 × 10¹² eV⁻¹ cm⁻².     

Effect of buffer layers on the property of Pb(Zr,Ti)O3-Pb(Mn,W,Sb,Nb)O3 thin films grown by pulsed laser deposition

New ferroelectric Pb(Zr,Ti)O₃-Pb(Mn,W,Sb,Nb)O₃ (PZT-PMWSN) thin film has been deposited on a Pt/Ti/SiO₂/Si substrate by pulsed laser deposition. Buffer layer was adopted between film and substrate to improve the ferroelectric properties of PZT-PMWSN films. Effect of a Pb(Zr_0.52Ti_0.48)O₃ (PZT) and (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) buffer layers on the stabilization of perovskite phase and the suppression of pyrochlore phase has been examined. Role of buffer layers was investigated depending on different types of buffer layer and thickness. The PZT-PMWSN thin films with buffer layer have higher remnant polarization and switching polarization values by suppressing pyrochlore phase formation. The remnant polarization, saturation polarization, coercive field and relative dielectric constant of 10-nm-thick PLT buffered PZT-PMWSN thin film with no pyrochlore phase were observed to be about 18.523 μC/cm², 47.538 μC/cm², 63.901 kV/cm and 854, respectively.     

Localized Surface Plasmon Resonance of Cu@Cu2O core-shell nanoparticles: Absorption, Scattering and Luminescence

By co-deposition via RF-Sputtering and RF-PECVD methods and using Cu target and acetylene gas, we prepared Cu@Cu₂O core-shell nanoparticles on the a-C:H thin film at room temperature. Mie absorption of Cu cores, scattering from Cu₂O shell and luminescence that rises from carrier transfer in Cu@Cu₂O interface were employed to fit the whole range of visible extinction spectrum of these core-shells. From simulation it was found that scattering and luminescence have an important effect on the energy, width and shape of LSPR absorption peak. Shift of LSPR peak is more affected by the dielectric coefficient of shell than Cu core size particularly for Cu core diameter above 4 nm. Also, the LSPR absorption peak is damped by decreasing Cu core size and dielectric coefficient of shell. The energy of LSPR absorption peak is independent of shell thickness and host dielectric coefficient. The LSPR peak is damped by increasing shell thickness and host dielectric coefficient too. The scattering contribution in extinction spectra was affected more by shell size than dielectric coefficient. These points are important for detection techniques based on LSPR peak.     

Spectral transmittance and module structure fitting for transmission-mode GaAs photocathodes

A transmission-mode GaAs photocathode includes four layers of glass,Si 3 N 4 ,Ga 1x Al x As and GaAs. A gradient-doping photocathode sample was obtained by molecular beam epitaxy and its transmittance was measured by spec-trophotometer from 600 nm to 1100 nm. The theoretical transmittance is derived and simulated based on the matrix formula for thin film optics. The simulation results indicate the influence of the transition layers and the three thin-film layers except glass on the transmittance spectra. In addition,a fitting coefficient needed for error modification enters into the fitted formula. The fitting results show that the relative error in the full spectrum reduces from 19.51% to 4.35% after the formula is modified. The coefficient and the thicknesses are gained corresponding to the minimum relative error,meanwhile each layer and total thin-film thickness deviation in the module can be controlled within 7%. The presence of glass layer roughness,layer interface effects and surface oxides is interpreted on the modification.