The optical properties of thin films of tantalum pentoxide and zirconium dioxide

The indices of refraction and absorption of thin films of tantalum pentoxide and zirconium dioxide have been determined in the wavelength range 250–2000 nm. These were obtained from the spectrophotometrically measured reflectance and transmittance of the films at normal incidence, using the method devised by Denton et al. The Ta₂O₅ films were amorphous and had smooth surfaces, and for these films analysis of the dependence of the absorption on photon energy has shown that there are band gaps of 4.15 and 4.51 eV. It is tentatively suggested that the observed absorption is due to direct transitions from a valence band with a spin-orbital splitting of 0.36 eV.

The ZrO₂ films were polycrystalline with rough surfaces and had to be treated as double layer films in order to obtain continuous dispersion curves. They were effectively transparent over the spectral range covered.     

Structure and optical properties of thin titanium films deposited on different substrates

Thin films of titanium were deposited on different substrates at room temperature. Measurements were made of the optical constants and of the transmittance of titanium films evaporated on to fused quartz. Films of titanium 10 to 40 nm thick were found to have quite uniform transmittance throughout the visible spectrum. Because titanium getters strongly during its evaporation, pure and compact titanium films can only be produced by fast evaporation under extremely good vacuum conditions. All films prepared for optical measurements, for X-ray and for scanning electron microscopy studies were, therefore, deposited at a pressure 10^–4 Pa and with deposition rate 4 nm sec^–1. The measurements were made using a Beckman double-beam spectrophotometer UV 5230, Siemens D 500 X-ray diffractometer, and SEMCO nanolab 7 scanning electron microscopy.     

Investigation of structural properties of ITO thin films deposited on different substrates

The influence of the substrate nature on the structure and morphology of ITO thin films grown by thermal evaporation in vacuum is investigated. The as-prepared metal films with Sn/In molar ratio of 0.1 were subsequently annealed for 2 h at 723 K in air (to obtain tin doped indium oxide), then annealed in vacuum at 523 K, followed by UV irradiation (to reduce the electrical resistivity). Irrespective of substrate nature, XRD data evidence a (222) preferential orientation in films. Substrate nature, annealing in vacuum and UV irradiation influence the structure, morphology, optical, electrical and surface wetting properties of the films' surface.     

Microstructure and physical properties of nanofaceted antimony doped tin oxide thin films deposited by chemical vapor deposition on different substrates

Antimony doped tin oxide SnO₂: Sb thin films have been fabricated by atmospheric pressure chemical vapour deposition at substrate temperature varying between 350 °C and 420 °C in a horizontal reactor, from a mixture of hydrated SnCl₂, SbCl₃ and O₂ gas. The films were grown on glass substrates and onto polished and porous n-type silicon. Doped films fabricated with various Sb (Sb/Sn %) contents ranging from undoped 0% to 4% were characterised employing different optical characterisation techniques, like X-ray diffraction, transmittance and reflectance in the wavelength range of 300 to 2500 nm and ellipsometry. The films exhibit the usual cassiterite diffraction pattern with high crystalline structure. Examination of the surface by scanning electron microscopy (SEM) showed that the films are textured made up of many pyramidal crystallites with nanofaceted surfaces, indicating highly stabilised material. The presence of inverted pyramids indicates that the crystallites grown by coalescence. The surface morphology was found to be independent on the kind of the substrate. From X-Ray spectra and SEM observations we get the texture the lattice constant and the grain size. The optical results provide information on film thickness, optical parameters and transmittance upon antimony concentration. The microstructure of the films, the grain growth topics (nucleation, coalescence…) depend strongly on deposition conditions and doping concentration. The observed variations of both the resistivity ρ and transmittance T are correlated to antimony atoms concentration which induced variation in the microstructure and in the size of SnO₂ nanograins (typically 20-40 nm). In this work, we have determined the feasibility of incorporating the correct amount of Sb atoms in tin oxide film by means of resistivity and transmission. SEM observations showed that the substrate do not affect the morphology.     

Pyrosol deposition of fluorine-doped tin dioxide thin films

Fluorine-doped tin dioxide (SnO₂F) films were deposited from a tin tetrachloride solution in methanol utilizing a pyrosol deposition process. It is shown from thermodynamic calculations that the atmosphere during deposition is oxygen-rich and also suggested that chlorine and hydrogen chloride, which are produced during the deposition reaction, influence crystal growth. Detailed electrical, optical and structural properties of the material with respect to varying film thickness and substrate temperature are presented and discussed. Resistivity of the films deposited at 450 °C decreased from 6×10^–4 to 2×10^–4 cm, while the mobility increased from 14 to 45 cm²V^–1s^–1, respectively, when the film thickness was varied from 100 to 1650 nm. The carrier concentration was relatively unchanged for film thicknesses higher than 200 nm. Optimized SnO₂F films (600 nm) having a resistivity of 6×10^–4 cm, a carrier mobility of 20 cm²V^–1s^–1, a carrier concentration of 8×10²⁰ cm^–3 and a transmittance in excess of 80% are quite suitable as electrodes for amorphous silicon solar cells.     

Pulsed laser deposition of thin films on actively cooled substrates

The paper deals with a special arrangement of pulsed laser deposition (PLD) when the substrates were cooled at cryogenic temperatures by liquid nitrogen during the deposition process. Applied materials – zinc oxide and titanium dioxide – play an important role in current optoelectronics and sensor research and a comparative study of their behaviour in presented PLD arrangements were performed.Prepared films (deposited on different substrates: Si (100) and sapphire) were investigated in as-deposited states and their properties in dependence of deposition temperature were compared. Investigation by X-ray diffraction and Raman spectroscopy proved their amorphous structure. Subsequently, annealing under different temperatures (up to 800 °C) was applied and properties of modified structures were compared by using different analytical methods (scanning electron microscopy, X-ray diffraction, Raman spectroscopy, optical absorption spectroscopy and spectroscopic ellipsometry).Pulsed laser deposition with cryogenic cooling of substrates opens a promising way for deposition of materials in non-equilibrium state. Such structures differ significantly between their counterparts despite of identical chemical composition. Annealing of such amorphous structures provide special conditions for studying of their recrystallization dynamics and controlling of their properties.     

The optical properties of zirconium diboride thin films

The optical properties of evaporated thin films of zirconium diboride were investigated from 4.1 to 11.3 eV. The optical constants were determined by reflectance measurements made at near-normal and oblique angles of incidence. The existence and energy of interband transitions and the plasma frequency are inferred from these results.     

Laser-ablated plasma for deposition of ZnO thin films on various substrates

We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on 1100) n-typesilicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser 1248 nm) atvarious pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.     

Laser-ablated plasma for deposition of ZnO thin films on various substrates

We report optical and structural properties of ZnO films deposited by pulsed laser deposition technique on (100) n-type silicon and quartz substrates at various pressures of back ground gas. ZnO plasma was created using KrF laser (248 nm) at various pressures of the ambient gas, oxygen. Laser induced plasma at varying fluence on the target was investigated using optical emission spectroscopy and 2-D images of the expanding plumes. X-ray diffraction, atomic force microscopy, and spectro-photometry were used to characterize as grown films.     

Chemical bath deposition of SnS thin films on ZnS and CdS substrates

We illustrate that Tin sulfide (SnS) thin films of 110–500 nm in thickness may be deposited on ZnS and CdS substrates to simulate the requirement in developing window-buffer/SnS solar cells in the superstrate configuration. In the chemical bath deposition reported here, tin chloride and thiosulfate are the major constituents and the deposition is made at 25 °C. In a single deposition, film thickness of 110–170 nm is achieved and in two more successive depositions, the film thickness is 450–500 nm. The thicker films are composed of vertically stacked flakes, 100 nm across and 10–20 nm in thickness. The Sn/S elemental ratio is ~1 for the films 110–170 nm in thickness, but it slightly increases for thicker films. The crystalline structure is orthorhombic, similar to the mineral herzenbergite, and with crystallite diameters 13 nm (110–170 films) and 16 nm (450–500 nm films). The Raman bands at 94, 172 and 218 cm^?1 further confirm the SnS composition of the films. The optical band gap of SnS is 1.4–1.5 eV for the thinner films, but is 1.28–1.39 eV for the thicker films, the decrease being ascribed to the increase in the crystallite diameter. Uniform pin-hole free SnS thin films were successfully grown on two different substrates and can be applied in solar cell structures.     

Chemical vapour deposition of nitrogen-doped titanium dioxide thin films

Nitrogen-doped titanium dioxide is often considered as a promising nanomaterial for photocatalytic applications. Here we report the first results of a study of APCVD of N-doped TiO2 thin films prepared with the use of ammonia as a source of nitrogen and titanium tetraisopropoxide (TTIP) as a source of Ti and O atoms. The obtained films were analyzed with X-ray diffraction, infrared spectroscopy, atomic force microscopy, X-ray photoelectron spectroscopy, UV-Vis spectroscopy, and ellipsometry. It was found that the film growth rate in the TTIP-NH3-Ar reaction system varied insignificantly with substrate temperature in the range of 450,..., 750 degrees C and did not exceed 4.4 nm/min. Yellow and orange layers with nitrogen content of about 7.6% were formed at the deposition temperature higher than 600 degrees C. The results of the structure analysis of the deposited films showed that addition of ammonia led to stabilization of the amorphous phase in the films. The effect of ammonia on optical and photocatalytic properties was also considered.     

Piezoresistive properties of nanocrystalline silicon thin films deposited on plastic substrates by hot-wire chemical vapor deposition

The piezoresistive property of n-type and p-type nanocrystalline silicon thin films deposited on plastic (PEN) at a substrate temperature of 150 °C by hot-wire chemical vapor deposition, is studied. The crystalline fraction decreased from 80% to 65% in p-type and from 84% to 62% in n-type films, as the dopant gas-to-silane flow rate ratio was increased from 0.18% to 3-3.5%. N-type films have negative gauge factor (− 11 to − 16) and p-type films have positive gauge factor (9 to 25). In n-type films the higher gauge factors (in absolute value) were obtained by increasing the doping level whereas in p-type films higher gauge factors were obtained by increasing the crystalline fraction.     

Electrical properties of thin PbTe films on Si substrates

An attempt was made to reduce the carrier concentration in thin PbTe films on Si substrates by optimizing deposition conditions. A modified hot-wall method was used for reproducible growth ofp-type films with 5 × 10¹⁵ < p(77 K) < 5 × 10¹⁷ cm^-3 andn-type films with 3 × 10¹⁵ < n(77 K) < 5 × 10¹⁶ cm^-3. The IR irradiation was found to have a significant effect on the temperature variation of film resistance. The activation energy of the IR-sensitivity centers was determined to be 0.11 ± 0.005 eV at room temperature and 0.18 ± 0.005 eV between 150 and 180 K.     

Chemical vapor deposition of phase-rich WC thin films on silicon and carbon substrates

Chemical vapor deposition was used to deposit tungsten carbide from a mixture of WCl₆, H₂ and C₃H₈ at 750-1050 °C on silicon and carbon substrates. The phase composition of the films was correlated with substrate temperature, substrate position in the reactor, and total flow rates. X-ray diffraction and X-ray photoelectron spectroscopy were employed to investigate the surface and bulk properties of the thin films. Thick, adherent films of phase-rich hexagonal WC were deposited using 1.3 × 10³ Pa total pressure, 1050 °C substrate temperature, and reactant flow rates of H₂/C₃H₈/Ar/WCl₆ = 1.8 × 10^− 2/3.6 × 10^− 3/8.9 × 10^− 4/1.8 × 10^− 4 mol/min, where Ar is the carrier gas. The surface composition was oxygen and carbon rich as compared with the bulk.     

Synthesis and characterization of vanadium oxide thin films on different substrates

In this study, the V₈O₁₅ derivative of vanadium oxide was produced on plain glass, indium tin oxide and silicon wafer substrate layers by taking advantage of wet chemical synthesis which is an easy and economical method. The structural properties of the produced films were examined by XRD and SEM analyses. Besides, Al/VO_x/p-Si metal-oxide-semiconductor (MOS) structure was obtained by the same synthesis method. Doping densities of these MOS structures were calculated from frequency dependent capacitance–voltage measurements. It was determined that the interface states which were assigned with the help of these parameters vary according to frequency.     

Structure and properties of nitrogen-doped titanium dioxide thin films grown by atmospheric pressure chemical vapor deposition

Using TiCl₄, O₂, and N₂O as precursors, N-doped titanium dioxide thin films with large area and continuous surface were obtained by atmospheric pressure chemical vapor deposition. Measurements of X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscope, transmission electron microscope and ultravoilet-Visible transmission spectra were performed. Using N₂O as N-doped source, anatase-rutile transformation is accelerated through oxygen vacancies formation, and the mean grain size of rutile crystallites decreases with the increase of N₂O flow rate. Compared to the pure TiO₂, N-doped TiO₂ films give a relative narrow optical band-gap, and their visible-light induced photocatalysis is much enhanced. Visible-light-induced hydrophilicity of the TiO₂ thin films enhances with the increase of N₂O flow rate, which might be due to the dentritic islands structure on the surface of the N-doped TiO₂ thin films.     

Nucleation and growth study of copper thin films on different substrates and wetting layers by metal-organic chemical vapour deposition

Chemical vapour deposition of copper thin films on different diffusion barrier/adhesion promoter layers have been studied. Copper thin films were grown in low pressure CVD reactor, using Cu(dpm)₂ as precursor and argon as carrier gas. Growth rates, film adhesion to the substrate, and surface morphology were studied in detail. Paper presented at the poster session of MRSI AGM VI, Kharagpur, 1995     

Optical and morphological properties of silicon dioxide thin films

The purpose of the present work is to compare the structural and optical properties of the Silicon dioxide films obtained from TMOS Si(OCH₃)₄), N₂O, and NH₃ as precursor gases, which with respect to their potential optical applications, have been deposited by using inductively coupled plasma-enhanced chemical-vapor deposition method. The optical property as well as the thickness of the films were analyzed by means of variable angle spectroscopic ellipsometry. Morphological studies were carried out by scanning electron microscopy, and chemical composition characterization was performed with the help of energy dispersive spectroscopy unit coupled with the electron microscope. The type of the substance and the precursor composition used for silicon dioxide synthesis are effective on the chemical composition of the films. The refractive index values of these films advocate their use as high refractive index materials while their low extinction coefficients assure the devices transparency. The work presents deposition rates as well as the films optical properties, chemical composition and morphology regarding the operational parameters of their synthesis. It also provides a comparison of the characteristics of the two competitive precursor compounds.     

Low-temperature deposition of ZnO thin films on PET and glass substrates by DC-sputtering technique

The structural, optical and electrical properties of ZnO thin films (260 - 490 nm thick) deposited by direct-current sputtering technique, at a relatively low-substrate temperature (363 K), onto polyethylene terephthalate and glass substrates have been investigated. X-ray diffraction patterns confirm the proper phase formation of the material. Optical transmittance data show high transparency (80% to more than 98%) of the films in the visible portion of solar radiation. Slight variation in the transparency of the films is observed with a variation in the deposition time. Electrical characterizations show the room-temperature conductivity of the films deposited onto polyethylene terephthalate substrates for 4 and 5 h around 0.05 and 0.25 S cm^− 1, respectively. On the other hand, for the films deposited on glass substrates, these values are 8.5 and 9.6 S cm^− 1 for similar variation in the deposition time. Room-temperature conductivity of the ZnO films deposited on glass substrates is at least two orders of magnitude higher than that of ZnO films deposited onto polyethylene terephthalate substrates under identical conditions. Hall-measurements show the maximum carrier concentration of the films on PET and glass substrate around 2.8 × 10¹⁶ and 3.1 × 10²⁰ cm^− 3, respectively. This report will provide newer applications of ZnO thin films in flexible display technology.