Conductive Tin Oxide Films Research Articles

Investigation of thermal stability, optical properties, phase and chemical composition of transparent conductive tin oxide films deposited by pyrolytic method on silica float glass

The object of research is transparent conductive coating based on fluorine doped tin oxide deposited on silica float glass by the pyrolytic method. However, both in the manufacturing process of such a coating and in the process of its operation, degradation of its electrically conductive properties is observed. This may be due to changes in the structure of the coating under the influence of certain technological and operational factors, namely: process temperature, holding time, gas environment during the application and operation of a transparent electrically conductive coating. Studies have confirmed a significant increase in electrical conductivity. They also found a slight decrease in the transmittance of transparent oxide-tin films obtained with the introduction of ammonium fluoride as a dopant during the pyrolysis of 1M alcohol solutions of Sn2+ and Sn4+chlorides and are widely used as precursors for the content of such coatings. So, with a ratio of Sn4+/F=10 in working solutions, a minimum of specific surface resistance was fixed at 32 Ohm/m2. At the same time, a decrease in the value of the averaged transmittance in the optical wavelength range of 0.2-6.0 μm by 51 %, and in its visible part (0.4-0.8 μm) by 11 %. It is shown that thermal degradation of the coating is a significant factor in increasing the resistance values both in the technological process and during operational impacts. The results obtained indicate that reheating to temperatures above 450 °C leads to the appearance of the phenomenon of thermal degradation of the electrically conductive properties of the coating. So, during a 1-hour exposure at a temperature of 550 °C, the increase in specific surface resistance increases by 2 times and is fixed at 68 Ohm/m2 after complete cooling. Repeated heating cycles with the indicated parameters lead to a significantly lesser effect, which may indicate stabilization of the processes that occur during thermal destruction of the electrically conductive coating.

P-Type highly conductive and transparent NdF3-doped tin oxide films prepared by dip coating

Transparent p-type conducting oxide (TCO) films with high conductivity and transparency are in great need to couple with n-type TCO for various electro-optical devices. The purpose of the current study is to explore p-type TCO films with low electrical resistivity and high optical transmittance. We prepared NdF3-added SnO2 (NFTO) thin films, with 0 to 5mol% NdF3, on a glass substrate by sol–gel dip-coating and post-annealed at 475°C. Structural, optical and electrical properties of the resultant NFTO films were investigated. X-ray diffraction patterns indicate tetragonal rutile SnO2 structure with a preferred (110) orientation for all studied films. The absence of impurity peaks indicates that Nd and F atoms may completely dissolve in SnO2 lattice. All films showed excellent transmittance of 84.7 to 90.6% at a wavelength of 550nm. Optical band gap of the NFTO films reduces from 3.94eV for un-doped film to a minimum of 3.75eV for the film with 4mol% NdF3. We confirmed p-type conduction of NFTO films using both Hall-effect and Seebeck coefficient measurements. The film with 2mol% NdF3 shows the lowest electrical resistivity, 8.2×10−3Ωcm, the highest hole-concentration, 8.96×1019cm−3 and a Hall mobility of 9.74cm2V−1s−1. The developed p-type NdF3 added SnO2 TCO films can couple with n-type SnO2 TCO for homo-junctions, which will lead to wide applications in optoelectronics.

The characteristics of CdxSn1 − xO films prepared by RF magnetron sputtering from powder targets

Transparent conductive cadmium and tin oxide films (CdxSn1−xO TCO) prepared by RF magnetron sputtering from the mixed oxide powder targets were with similar compositions to those of the targets. The morphological structures of the films were columnar in the grain sizes over 100nm. New phrases were formed for the films with proper metallic ratio, i.e. x=0.5 and 0.7 and the mixture of nano-crystal and amorphous structure might exist. Also, the nano-crystal structure with severe lattice deformation could be seen in the x=0.2 and 0.8 films, and all nano-crystals were in domain sizes about 10–20nm. Other multi-component films were with amorphous structure. The average transmittance of the films within the visible wavelength, except for the pure CdO film, was over 80%. The concentrations of electrons of these n-type CdxSn1−xO films were in the order of 1020cm−3. Without considering of the pure CdO and SnO2 films, the high mobilities (up to 50cm2/Vs) can be obtained from the films with amorphous structure. The resistivities of the films decreased from 10−3 to 10−4Ω·cm with the increases of Cd ratios in the films.

Low temperature sputter deposition of SnOx:Sb films for transparent conducting oxide applications

SnOx:Sb films have been prepared by reactive dc magnetron sputtering from a metallic target, with the aim of evaluating the potential of SnOx:Sb as an attractive low-cost alternative to In2O3:Sn (ITO) for TCO applications. The deposition was performed without any additional heating of the substrates. The films were subsequently analysed regarding their optical, electrical and structural properties. Our results show that there is only a narrow process window for the sputter deposition of transparent and conducting tin oxide films at low temperature. A sharp minimum in resistivity of 4.9mΩcm is observed at an oxygen content of approximately 17% in the sputtering gas. Under these deposition conditions, the SnO2:Sb films turn out to be both highly transparent and crystalline. At lower oxygen content (10–15%) the SnOx:Sb films are substoichiometric, as revealed by Rutherford backscattering, and show a low transmission and high resistivity due to numerous defects and the presence of the SnO phase. At higher oxygen content (>17%) excess oxygen is incorporated into the films, which is attributed to an increase of oxygen ion bombardment. This leads to a degradation of the electrical properties and a decrease of the density of the films, whilst the optical transmittance slightly improves.

Deposition of transparent, conductive tin oxide films on glass using a radio-frequency induction heater

Tin oxide films are often used as transparent, conductive coatings on glass in the scientific research setting. The standard approach of depositing these films in an oven leads to poor visibility of the substrate and thus inhibits the ready formation of uniform, low resistivity films. In this note we describe a simple tin oxide film deposition technique using a radio-frequency induction heater that allows for in situ visualization of the deposition process and resulting film. Uniform films having resistivities as low as 2 mohm cm with transmittances of approximately 85% in the visible light spectrum were readily deposited.

Doped-Fluorine on Electrical and Optical Properties of Tin Oxide Films Grown by Ozone-Assisted Thermal CVD

Transparent conductive fluorine-doped tin oxide (FTO, ) films were grown using a low-pressure metallorganic chemical vapor deposition (LP-MOCVD) with tetramethyltin (TMT), oxygen containing ozone , and hydrofluoric acid (HF) as a dopant. Using ozone contained oxygen instead of pure oxygen, the substrate temperature could be reduced by while maintaining a growth rate similar to that of tin oxide film. Growth rate of FTO film increased with the flow rate of TMT, however, adherence strength between the film and glass decreased. Resistivity of FTO thin films decreased with the TMT and HF flows over most of ranges investigated, while the resistivity increased rapidly with respect to excessive flow of the TMT over 300 sccm. Optical transmittance of FTO film was about 80% at , and the variation as a function of HF flow rate was not significant. FTO film prepared at an optimum condition showed a minimum resistivity of , a mobility of , and a carrier concentration of .

Scattering mechanism of transparent conducting tin oxide films prepared by magnetron sputtering

Undoped SnO2−x thin films with amorphous phase were prepared at room temperature by radio frequency magnetron sputtering, and the changes in electrical, optical and structural properties were investigated upon annealing in atmosphere. The amorphous SnO2−x film had the minimum resistivity of 1.5×10−3 Ω cm and the highest Hall mobility of 22 cm2/V s, which were comparable to those observed in polycrystalline doped SnO2 films. Examination of the temperature dependent Hall mobility revealed the grain boundary scattering as the dominant scattering mechanism for the crystallized SnO2−x films. Analysis made by using four coefficients instrument showed that undoped SnO2−x films had the characteristics of degenerate semiconductor with non-parabolic band structure, and that ionized impurity scattering with free electron screening was dominant mobility limiting mechanism in amorphous SnO2−x films.

Development of A Novel Solid-State pH Sensor Based on Tin Oxide Thin Film

Abstract A solid-state pH sensor was fabricated using a transparent conductive tin oxide film on a glass substrate. The coating of the glass substrate was achieved by a novel simple chemical vapor deposition (CVD) procedure. The response time of the pH sensor was substantially reduced when a thin graphite film was deposited onto the tin oxide conductive film. The sensor slope was found to increase as the temperature of the solution was increased. The performance of the sensor was investigated in the pH range from 0.3 to 11.0. A straight-line calibration graph was achieved throughout the whole range tested, especially when the solution temperature was 80 ℃. The working pH range was found to decrease on the expense of the lower range as the temperature was decreased. Results obtained by the suggested sensor compares very well with conventional pH electrodes where the square of the correlation coefficient was 0.999.

Low-temperature growth of highly crystallized transparent conductive fluorine-doped tin oxide films by intermittent spray pyrolysis deposition

Following the procedure by Sawada et al. (Thin Solid Films 409 (2002) 46), high-quality SnO2:F films were grown on glass substrates at relatively low temperatures of 325–340°C by intermittent spray pyrolysis deposition using a perfume atomizer for cosmetics use. Even though the substrate temperature is low, as-deposited films show a high optical transmittance of 92% in the visible range, a low electric resistivity of 5.8×10−4 Ω cm and a high Hall mobility of 28 cm2/V s. The F/Sn atomic ratio (0.0074) in the films is low in comparison with the value (0.5) in the sprayed solution. The carrier density in the film is approximately equal to the F-ion density, suggesting that most of the F-ions effectively function as active dopants. Films’ transmittance and resistivity show little change after a 450°C 60 min heat treatment in the atmosphere, evidencing a high heat resistance. The SnO2:F films obtained in this work remove the difficulty to improve the figure of merit at low synthesis temperatures.

Modelling and experimental study of an O 2/Ar/tetramethyltin discharge used for the deposition of transparent conductive thin tin oxide films

Non-stoichiometric tin oxide thin films were deposited from an O 2/Ar/tetramethyltin (TMT) mixture in a RF glow discharge parallel plate reactor at low pressure (15 Pa) and low temperature (25–80 °C). The aim of this work was to determine the role of the experimental parameters such as the absorbed power, bias voltage and feed gas composition on the electron density and the atomic oxygen mole fraction, two parameters which play an important role on the TMT decomposition and carbon stripping of the deposited films. Since TMT concentration is typically less than 2% a first study was carried out from both experimental and modelling point of view for the O 2–Ar mixture. Experimental investigations included optical emission spectroscopy, mass spectrometry, and electrical diagnostics. A numerical quasi-homogeneous (0D) model and a self-consistent 1D fluid model were used for comparison. The optimisation of the thin film deposition process was discussed briefly on the basis of the obtained results.

Development of tin oxide synthesis by plasma-enhanced chemical vapor deposition

Transparent conducting oxide (TCO) thin films have been synthesized to date primarily by either physical vapor deposition or thermal chemical vapor deposition. Plasma-enhanced chemical vapor deposition (PECVD) offers potential advantages over these techniques, but it has not been applied extensively to TCO synthesis. In this article we report on the use of PECVD to deposit transparent, conducting tin oxide films from mixtures of SnCl4 and O2. These films were deposited on glass substrates at temperatures between 150 and 350 °C. The growth rate, optical, electrical, and structural properties were examined as a function of plasma power, substrate temperature, and gas composition. Increasing rf power revealed a rise in deposition rate with no effect on electrical properties, while both substrate temperature and oxygen flow rate were found to significantly influence resistivity. The effect of annealing was also examined, and it was found that annealing at 250 °C significantly improved the electrical properties. The optical transparency of all films was greater than 86% in the visible spectrum, and electrical resistivities as low as 2.1×10−3 Ω cm have been achieved.

Effect of fluorine doping and spraying technique on the properties of tin oxide films

The aim of the present work is to prepare transparent and conductive tin oxide film using an inexpensive method. The effect of different doping levels of fluorine (from 0 to 120 at.%) is ascertained and post heat treatment is carried out. Films are also investigated as a function of concentration of tin precursor (0.1–1.6 M SnCl 4). The electrical and optical properties of the films with different concentrations of tin tetrachloride are discussed. The sheet resistance of the film deposited at 450°C decreases by increasing the concentration of SnCl 4. It is also found that the film has a transparency of about 80%, which makes it suitable for different applications. The optimized SnO 2:F atomic percent ratio films produced a sheet resistance of 0.3×10 3 ohm/□). The X-ray diffraction patterns showed that the preferred orientation is [200], but it changes to [301] for heat-treated films.

Identification of Mercury Reaction Sites in Fluorescent Lamps

The interaction between Hg and components in fluorescent lamps was studied using electron spectroscopy for chemical analysis (ESCA) and sputtered neutral mass spectrometry (SNMS). Active sites, which were responsible for Hg interaction/deposition, were identified by comparison of the X‐Y distribution (obtained by ESCA mapping) and depth distribution (available through SNMS) of respective lamp components with that of Hg. These results showed that Hg strongly interacted with Na (from glass) and the emitter components, especially Ba. In the case of lamps with a tin oxide conductive film, the film was also a source for interaction. Exact assignment of the oxidation state for the interacted Hg species was not certain due to a small variation in binding energy shift among the Hg compounds. However, the data suggested an Hg(0) state. It was possible that most of the Hg species strongly chemisorbed onto Ba (and/or Sr) and Na sites or formed intermetallic compounds with these elements. © 1999 The Electrochemical Society. All rights reserved.

Tin Oxide Films Deposited by Ozone-Assisted Thermal Chemical Vapor Deposition

Transparent conductive tin oxide (TO, SnO2) films have been prepared by low pressure metal organic chemical vapor deposition (LP-MOCVD) from various mixtures of tetramethyltin (TMT) with oxygen and oxygen containing 2.96 to 5.1 mol% O3. The properties of TO films have been changed with the gas flow rate (oxygen, oxygen containing ozone) and the substrate temperature. The use of oxygen containing ozone instead of pure oxygen reduced substrate temperature significantly and the resistivity while maintaining the same growth rate. The films prepared using ozone showed resistivity ranging from 10-2 to 10-3 Ωcm, and ranging mobility from 10.5 to 13.7 cm2/Vs.

Transparent conductive tin oxide films by photochemical vapour deposition

Photochemical vapour deposition (photo-CVD) is expected to be a damage-free process at low temperature. Transparent conductive tin oxide (non-doped) films have been prepared by the photo-CVD process under various deposition conditions. TMT (Sn (CH 3) 4) and O 2 (containing 4 mol.% O 3) were used as the raw materials and a low-pressure mercury lamp was used as the light source. By the combination of linearly focused low-pressure mercury lamp light through a semi-cylindrical suprasil window and a reciprocation motion of the substrate, a good uniformity of the film thickness along an 8 × 10 cm area was realised. The growth rate was proportional to both the substrate temperature and the TMT flow rate. The minimum resistivity of ~ 7 × 10 −3 Ω cm was obtained at a substrate temperature of 250 °C.

Microcrystalline thin metal oxide films for optoelectronic applications

We report the properties and optoelectronic applications of transparent and conductive indium and tin oxide films prepared by the spray pyrolysis method and doped with Sn or F, respectively. The film properties have been measured using X-ray diffraction, optical and electrical absorption. As examples of applications we produced a set of selective optical detectors for different spectral regions, covering the wavelength range from 0.25 to 1.1 μm, based on metal oxide-semiconductor heterostructures and using different substrates such as: GaP, GaSe, Al x Ga 1− x As, GaAs and Si. The fabricated devices exhibit several features such as: production simplicity, high quantum efficiency, uniform sensitivity over the entire active area and a high response speed. Finally, we present a high quantum efficiency and solar blind monocrystalline zinc sulphide optical sensor fabricated by spray deposition as an alternative to the ultraviolet-enhanced SiC and GaN photodetectors and the performances of a solar cell.

Directed Photocurrents in Nanostructured TiO2/SnO2 Heterojunction Diodes

Time-resolved photocharge (TRPC) measurements are applied for the first time to demonstrate the presence of a contact potential between lightly sintered colloidal nanocrystalline TiO2 films deposited on transparent highly conductive tin oxide films degenerately doped with fluorine, SnO2(F). By virtue of its contactless nature and absence of an externally applied field, TRPC has previously been demonstrated to possess the capability to directly probe the electric field in semiconductor heterojunction particulate materials without the complications and ambiguities encountered with many other measurement techniques. Using TRPC, vectorial directions of photoelectron currents in glass/SnO2(F)/TiO2 samples, as determined by signal polarity, are found to be dependent on their orientation with respect to the incident photon flux (i.e., negative polarity for exposure through the glass; positive polarity for exposure directly on the TiO2). This implies that photoelectrons always flow toward the SnO2(F)/TiO2 interfa...

Highly conductive transparent F-doped tin oxide films were prepared by photo-CVD and thermal-CVD

Although high-quality SnO 2 films have been prepared above 400°C, we prepared highly-conductive transparent F-doped SnO 2 films below about 350°C and at high growth rates, using a new raw material system of Sn(CH 3) 4, O 2 containing 5 mol.% O 3, and HF-acid. At a substrate temperature of 350°C, the films, which had properties such as sheet resistances of 1.6 and 4.5 Ω/□, resistivities of 3.4 and 4.5 × 10 −4 Ωcm, and transmittances including substrates of 70% and 80% at 550 nm, were prepared by thermal-CVD and photo-CVD (chemical vapour deposition), respectively. Several optical and electrical properties of the films prepared by both CVD methods were compared.

Arc behaviour during filtered vacuum arc deposition of Sn-O thin films

Sn−O transparent, conductive thin films were produced in a filtered vacuum-arc deposition system, consisting of a 90 mm diameter cathode, 122 mm diameter annular anode, and a magnetic quarter torus macroparticle filter. Arc current was in the range 30–200 A and the toroidal magnetic field ( B T) was in the range 0–25 mT. A radial magnetic field ( B r) at the cathode surface was produced by a coil placed inside a cavity in the cathode. Cathode spot motion, plasma jet motion through the toroidal field, and the characteristics of the deposited Sn−O films were studied as a function of arc current, applied magnetic fields and oxygen pressure. Cathode spot motion on the cathode surface was controlled by B T. Random spot motion on the entire cathode surface was obtained in vacuum when Br was less than 2 mT. The spots were forced to move on a circular path with average radius of 25 mm when B r was larger than 2 mT. Cathode surface oxidation occurred when oxygen was introduced into the system, and its rate increased with the gas pressure. The extent of the oxidized area on the cathode surface was affected not only by gas pressure, but also by the magnitude of arc current and the magnetic fields B r and B T. With B r smaller than 2 mT, oxidized surface regions appear on the cathode, and cathode spot activity on them is disturbed. Random cathode spot motion continues undisturbed on non-contaminated regions of the cathode surface. Cathode spots were hardly observed on the oxidized regions, yet visual examination of the cathode surface used in the arc revealed the existence of cathode spots erosion tracks on them. Transparent and conductive tin oxide films were produced at oxygen pressures of 0.8 Pa when arc operation and the plasma jet in the filter were stable. The stability of the arc and the plasma jet were found to depend on the combination of gas pressure, arc current and magnetic fields. When the plasma jet was not stable poorly conductive films were produced, containing the non-conductive oxide SnO.

Arc behaviour during filtered vacuum are deposition of Sn-O thin films

Sn−O transparent, conductive thin films were produced in a filtered vacuum-arc deposition system, consisting of a 90 mm diameter cathode, 122 mm diameter annular anode, and a magnetic quarter torus macroparticle filter. Arc current was in the range 30–200 A and the toroidal magnetic field (BT) was in the range 0–25 mT. A radial magnetic field (Br) at the cathode surface was produced by a coil placed inside a cavity in the cathode. Cathode spot motion, plasma jet motion through the toroidal field, and the characteristics of the deposited Sn−O films were studied as a function of arc current, applied magnetic fields and oxygen pressure. Cathode spot motion on the cathode surface was controlled by BT. Random spot motion on the entire cathode surface was obtained in vacuum when Br was less than 2 mT. The spots were forced to move on a circular path with average radius of 25 mm when Br was larger than 2 mT. Cathode surface oxidation occurred when oxygen was introduced into the system, and its rate increased with the gas pressure. The extent of the oxidized area on the cathode surface was affected not only by gas pressure, but also by the magnitude of arc current and the magnetic fields Br and BT. With Br smaller than 2 mT, oxidized surface regions appear on the cathode, and cathode spot activity on them is disturbed. Random cathode spot motion continues undisturbed on non-contaminated regions of the cathode surface. Cathode spots were hardly observed on the oxidized regions, yet visual examination of the cathode surface used in the arc revealed the existence of cathode spots erosion tracks on them. Transparent and conductive tin oxide films were produced at oxygen pressures of 0.8 Pa when arc operation and the plasma jet in the filter were stable. The stability of the arc and the plasma jet were found to depend on the combination of gas pressure, arc current and magnetic fields. When the plasma jet was not stable poorly conductive films were produced, containing the non-conductive oxide SnO.