Optical characterization of vanadium-titanium oxide films

Composite films of titanium and vanadium oxides (TVO) with various compositional ratios were prepared by sputtering deposition. The optical properties, crystalline structure and film morphology were investigated as a function of the composition. The results of thermochromism and X-ray diffraction suggest that the TVO films at any compositional ratios form substitutional solid solution of Ti and V, that is, Ti_xV_1−xO₂, where 0 ≤ x ≤ 1. Dielectric constants of the TVO films at any compositions were consistently determined at photon energies between 0.75 to 3 eV by employing the Lorentz-oscillator formula. With wide variation in x, the dielectric constants at visible and near-infrared wavelengths monotonically decrease down to the values of TiO₂, which suggests that dielectric constants of the TVO film can be precisely controlled by adjusting rf power in co-sputtering deposition.     

Optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films

The paper presents the optical properties of amorphous-like indium zinc oxide and indium gallium zinc oxide thin films with various In/(In + Zn) ratios obtained by Pulsed Laser Deposition. Thickness results obtained from simulations of X-ray Reflectivity and Spectroscopic Ellipsometry data were very similar. The dependence of density on stoichiometry resembles the corresponding dependence of the refractive index in the transparency range. A free carrier absorption was noted in the visible spectral range, leading to a weak absorbing thin transparent conductive oxide. On the other hand, the refractive index is smaller than those of based oxides (ZnO and In₂O₃), and counterbalance therefore the weak light absorption.     

Optical properties of thin films of mixed Ni-W oxide made by reactive DC magnetron sputtering

Thin films of Ni_xW_1 − x oxides with x = 0.05, 0.19, 0.43 and 0.90 were studied. Films with thicknesses in the range 125-250 nm were deposited on silicon wafers at room temperature by reactive DC magnetron co-sputtering from targets of Ni and W. The films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM), and spectroscopic ellipsometry (SE). XRD spectra and SEM micrographs showed that all films were amorphous and possessed a columnar structure. The ellipsometric angles Ψ and Δ of as-deposited films were measured by a rotating analyzer ellipsometer in the UV-visible-near infrared range (0.63-6.18 eV) and by an infrared Fourier transform rotating compensator ellipsometer in the 500-5200 cm⁻¹ wavenumber range. SE measurements were performed at angles of incidence of from 50 ° to 70 °. Parametric models were used to extract thicknesses of the thin films and overlayers of Ni_xW_1 − x oxide at different compositions, band gaps and optical constants. Features in the optical spectra of the Ni_xW_1 − x oxides were compared with previous data on tungsten oxide, nickel oxide and nickel tungstate.     

Optical properties of silicon thin films related to LPCVD growth condition

In this paper we study the changes in the microstructural and optical properties of silicon thin films produced by the variation of the parameters (temperature and pressure) of the low-pressure chemical vapour deposition (LPCVD) process. Silicon thin films prepared by LPCVD on oxidized silicon substrates over a large range of process parameters (T_dep=500-615°C, p_dep=20-100 Pa) have been characterized by Raman spectroscopy, spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and atomic force microscopy (AFM) techniques. The phase transition of as-deposited silicon from an amorphous to a crystalline phase via an intermediate mixed phase (few grains in amorphous silicon matrix) can be monitored by the changes in the optical properties and in the Raman spectra. LPCVD parameters, which control the deposition kinetics, are able to influence the optical properties, the structure and/or morphology of the as-deposited LPCVD silicon films. The SE and Raman results prove that it is possible to grow by LPCVD (from pure silane), a silicon film in a (poly)crystalline state at a temperature as low as 500°C.     

Refractive indices of textured indium tin oxide and zinc oxide thin films

The refractive indices of textured indium tin oxide (ITO) and zinc oxide (ZnO) thin films were measured and compared. The ITO thin film grown on glass and ZnO buffered glass substrates by sputtering showed distinct differences; the refractive index of ITO on glass was about 0.05 higher than that of ITO on ZnO buffered glass in the whole visible spectrum. The ZnO thin film grown on glass and ITO buffered glass substrates by filtered vacuum arc also showed distinct differences; the refractive index of ZnO on glass was higher than that of ZnO on ITO buffered glass in the red and green region, but lower in the blue region. The largest refractive index difference of ZnO on glass and ITO buffered glass was about 0.1 in the visible spectrum. The refractive index variation was correlated with the crystal quality, surface morphology and conductivity of the thin films.     

Effect of film thickness on properties of aluminum doped zinc oxide thin films deposition on polymer substrate

A series of aluminum doped zinc oxide thin films with different thickness (25–150 nm) were deposited on indium tin oxide coated polyethylene terephthalate substrates by radio frequency magnetron sputtering method at room temperature. The structural, optical and electrical properties of the films were investigated by X-ray Diffractometer, UV–Vis spectrometer and Hall Effect Measurement System. All the obtained films were polycrystalline with a hexagonal structure and a preferred orientation along [002] direction with the c-axis perpendicular to the substrate surface. The optical energy band gap (E_g) values of the films were found to be in the range from 3.36 to 3.26 eV, and their average optical transmissions were about 75 % in the visible region. The films had excellent electrical properties with the resistivities in the range from 2.78 × 10^?5 to 2.03 × 10^?4 Ω cm, carrier densities more than 3.35 × 10²¹ cm^?3 and Hall mobilities between 5.77 and 11.13 cm²/V s.     

Comparative study of zinc oxide and aluminum doped zinc oxide transparent thin films grown by direct current magnetron sputtering

Pure and aluminum (Al) doped zinc oxide (ZnO and ZAO) thin films have been grown using direct current (dc) magnetron sputtering from pure metallic Zn and ceramic ZnO targets, as well as from Al-doped metallic ZnAl2at.% and ceramic ZnAl2at.%O targets at room temperature (RT). The effects of target composition on the film's surface topology, crystallinity, and optical transmission have been investigated for various oxygen partial pressures in the sputtering atmosphere. It has been shown that Al-doped ZnO films sputtered from either metallic or ceramic targets exhibit different surface morphology than the undoped ZnO films, while their preferential crystalline growth orientation revealed by X-ray diffraction remains always the (002). More significantly, Al-doping leads to a larger increase of the optical transmission and energy gap (E_g) of the metallic than of the ceramic target prepared films.     

Spectroscopic ellipsometry study of CuCdTeO thin films grown by reactive co-sputtering

The complex dielectric function of CdTeO_x and CuCdTeO thin films was determined by spectroscopic ellipsometry in the photon energy range of 1.5 to 5 eV. The films were grown onto glass slides substrates by reactive rf co-sputtering using CdTe and Cu targets in an Ar + O₂ atmosphere. Films with different Cu concentrations were obtained by varying the power on the Cu target. The dielectric function of the films is represented by a generalized Lorentz harmonic oscillator expression. Three-dimensional type line-shapes for the critical points E₁ and E₁ + Δ₁ of CdTe were identified in CdTeO_x and CuCdTeO films even for Cu and O concentrations above 20 at.%. This latter result can be indicative of CdTe alloying with those elements widening the possibilities for new photovoltaic materials.     

Al浓度对AZO薄膜结构和光电性能的影响

采用射频溅射方法在Si基片上制备出AZO掺杂薄膜,对薄膜进行了XRD和AFM分析,并对其电性能作了研究.结果表明,掺杂量低于15%(原子分数)时,AZO薄膜结构为纤锌矿结构,呈c轴方向择优生长,没有Al2O3相出现.薄膜的可见光透过率均在80%以上,其最高电阻率出现在掺杂量为30%(原子分数),为1.3×107 Ω·cm.     

Optical properties of bismuth niobate thin films studied by spectroscopic ellipsometry

We performed optical analysis of bismuth niobate thin films using spectroscopic ellipsometry (SE). The films were grown on Pt/Ti/SiO₂/Si substrates with pulsed laser deposition. Six films were prepared using various deposition temperatures and thermal-annealing times. The room-temperature SE spectra of these films were measured by a rotating-analyzer ellipsometer from 1.12 to 6.52 eV at incidence angles of 50, 55, 60, 65, and 70°. The resulting refractive indices and extinction coefficients show significant changes with deposition temperature and thermal annealing.     

Optical, structural and electrical properties of Mn doped tin oxide thin films

Mn doped SnO_x thin films have been fabricated by extended annealing of Mn/SnO₂ bilayers at 200°C in air for 110 h. The dopant concentration was varied by controlling the thickness of the metal layer. The overall thickness of the film was 115 nm with dopant concentration between 0 and 30 wt% of Mn. The films exhibit nanocrystalline size (10-20 nm) and presence of both SnO and SnO₂. The highest transmission observed in the films was 75% and the band gap varied between 2.7 and 3.4 eV. Significantly, it was observed that at a dopant concentration of ∼4 wt% the transmission in the films reached a minimum accompanied by a decrease in the optical band gap. At the same value of dopant concentration the resistivity also reached a peak. This behaviour appears to be a consequence of valence fluctuation in Sn between the 2+ and 4+ states. The transparent conductivity behaviour fits into a model that attributes it to the presence of Sn interstitials rather than oxygen vacancies alone in the presence of Sn^{2 +}.     

Optical properties of porous anodic aluminum oxide thin films on quartz substrates

Porous anodic aluminum oxide (AAO) thin films on quartz substrates were fabricated via evaporation of a 100-nm thick Al, followed by anodization with different durations and pore widening and Al removal by chemical etching. The transmittance and reflectance of AAO films on quartz substrates were measured by optical spectrophotometry. The microstructure and morphology were examined by scanning electron microscopy. The pore diameter of AAO films after pore widening and Al removal is 60 ± 4 nm and the interpore distance is 88 ± 5 nm. It is found that the reflectance decreases and the transmittance increases with the increase of the anodization time and pore widening. Compared to a bare substrate, the transmittance of AAO films after pore widening and Al removal is about 3.0% higher, while the reflectance is about 3.0% lower over a wide wavelength range. Additionally, after pore widening and Al removal, when AAO films are prepared on both sides of the quartz substrate, the highest transmittance is about 99.0% in the wavelength range 570-680 nm. The optical constants and thickness of AAO films after pore widening and Al removal were retrieved from normal incidence transmittance data. Results show that the refractive index is lower than 1.25 in the visible optical region and that the porosity is about 0.70.     

Microstructure and hemocompatibility of neodymium doped zinc oxide thin films

By the radio frequency magnetron sputtering, both un-doped and neodymium (Nd) doped ZnO thin films were grown on Si (100) substrates. The microstructure of the films has preferred c-axis growth orientation confirmed by the X-ray diffraction spectra. The crystallite size of ZnO crystallite decreases with the increasing of Nd concentration. We show that the hemocompatibility can be improved by a suitable Nd doping in the ZnO thin films. It is verified by both calculations on surface energy and interfacial tension of the sample, and experiments on the wettability, the proteins adsorption, and the platelets adhesion.     

Spectral properties of aluminium doped zinc oxide thin films prepared by SILAR method

The spectral properties of undoped and Al doped ZnO nano thin films prepared using double dip method otherwise called SILAR method (Successive Immersion Layer Adsorption Reaction) are reported. The thin films were having polycrystalline hexagonal structure. The optical properties of these films are studied and reported. The optical constants like the band gap (E _g ), refractive indices (n, k), dielectric constant (ε), optical conductivity (σ), were estimated using an approximation algorithm developed from established procedures using transmittance spectrum of the thin films. The average excitation energy (E ₀), oscillator strength (E _d ), effective mass (m*), plasma frequency (ω _p ), static dielectric constant (ε_∞) and carrier concentration (N) are also estimated and reported. The highly transparent thin films showed nanowires protruding from stacked nanorods on SEM inspection that signifies the suitability of these thin films for gas sensors.     

Indium doped zinc oxide thin films obtained by electrodeposition

Indium doped ZnO thin films were obtained by co-electrodeposition (precursor and dopant) from aqueous solution. XRD analysis showed typical patterns of the hexagonal ZnO structure for both doped and undoped films. No diffraction peaks of any other structure such as In₂O₃ or In(OH)₃ were found. The incorporation of In into the ZnO film was verified by both EDS and XPS measurements. The bandgap energy of the films varied from 3.27 eV to 3.42 eV, increasing with the In concentration in the solution. This dependence was stronger for the less cathodic potentials. The incorporation of In into the film occurs as both, an In donor state in the ZnO grains and as an amorphous In₂O₃ at the grain boundaries.     

Effects of post-rapid thermal annealing on structural, electrical and optical properties of hydrogenated aluminum doped zinc oxide thin films

In this study, hydrogenated aluminum doped zinc oxide (HAZO) thin films were prepared by DC magnetron sputtering in different H₂/(Ar+H₂) volume ratio atmosphere. The effects of post-rapid thermal annealing (RTA) in Ar+8 % H₂ atmosphere on the structural, optical, and electrical properties of the thin films were investigated systematically. Results showed that the RTA treatment effectively improved the electrical conductivity of the HAZO thin films with small hydrogen content, due to the increase of the Hall mobility and the carrier concentration. The lowest resistivity of the HAZO thin film deposited in 8 % H₂ ratio atmosphere reached 6.3 × 10^?4 Ω cm after RTA. The improved electrical properties of the RTA-treated HAZO films were ascribed to the activation of Al dopants, the increase of oxygen vacancies and the desorption of negative charged oxygen species at the grain. These results implied that RTA process might be useful to fabricate high quality HAZO films with a low thermal budget.     

Optical properties of pyrene doped polymer thin films

Thin films of pyrene in polystyrene matrix have been prepared by spin coating technique. The concentration of polystyrene is kept constant to 1 wt.% while that of pyrene dopant varied in the range 2.30×10⁻⁴-2.30×10⁻¹ wt.%. Thickness of the films was found to depend upon concentration of pyrene and varies from 90 to 782 nm. The results of X-ray diffraction analysis reveal the crystalline nature of the films. The optical properties were studied by absorption, excitation and fluorescence spectroscopy. The band gap energy of pyrene in polymer films was calculated from absorption results. A transition from monomer to excimer is observed with thickness variation of the films. The structured part of the spectrum is assigned to the monomer emission while the broad emission band is attributed to well known pyrene excimer-like emission.     

Electrical mechanism analysis of Al2O3 doped zinc oxide thin films deposited by rotating cylindrical DC magnetron sputtering

Cost efficient and large area deposition of superior quality Al₂O₃ doped zinc oxide (AZO) films is instrumental in many of its applications, including solar cell fabrication due to its numerous advantages over indium tin oxide (ITO) films. In this study, AZO films were prepared by a highly efficient rotating cylindrical direct current (DC) magnetron sputtering system using an AZO target, which has a target material utilization above 80%, on glass substrates in argon (Ar) ambient. A detailed analysis on the electrical, optical, and structural characteristics of AZO thin films was performed for the solar cell, as well as display applications. The properties of films were found to critically depend on deposition parameters, such as sputtering power, substrate temperature, working pressure, and film thickness. A low resistivity of ~ 5.5 × 10^− 4 Ω cm was obtained for films deposited at 2 kW, keeping the pressure, substrate temperature and thickness constant at 3 mTorr, 230 °C and ~ 1000 nm respectively. This was due to an increase in carrier mobility and large grain size. Mobility is found to be controlled by ionized impurity scattering within the grains, since the mean free path of carriers is much smaller than the grain size of the films. The AZO films showed a high transparency of ~ 90% in the long wavelength region. Our results offer a cost-efficient AZO film deposition method that can fabricate films with significant low resistivity and high transmittance that can be applied in thin-film solar cells, as well as thin film transistor (TFT) and non-volatile memory (NVM).     

Optical characterization of thin chalcogenide films by multiple-angle-of-incidence ellipsometry

Optical properties of thin chalcogenide films from the systems As-S(Se) and As-S-Se were investigated as a function of the film composition, film thickness and conditions of illumination by light using multiple-angle-of-incidence ellipsometry. Thin films were deposited by thermal evaporation and exposed to white light (halogen lamp) and to monochromatic light from Ar⁺ — (λ = 488, 514 nm) and He-Ne- (λ = 632.8 nm) lasers. The ellipsometric measurements were carried out at three different angles of light incidence in the interval 45-55°, at λ = 632.8 nm. An isotropic absorbing layer model was applied for calculation of the optical constants (refractive index, n and extinction coefficient, k) and film thickness, d. The homogeneity of the films was checked and verified by applying single-angle calculations at different angles. It was shown that the refractive index, n of As-S-Se films is independent of film thickness in the range of 50 to 1000 nm and its values varied from 2.45 to 3.05 for thin layers with composition As₂S₃ and As₂Se₃, respectively. The effect of increasing in the refractive index was observed after exposure to light which is related to the process of photodarkening in arsenic containing layers. The viability of the method for determining the optical constants of very thin chalcogenide films with a high accuracy was confirmed.