Thin tin oxide films of low conductivity prepared by chemical vapour deposition

Homogeneous SnO₂ films were produced from dibutylin diacetate by chemical vapour deposition at rates of 10–30 nm min^?1. The films obtained had conductiveties between 3 and 25Ω^?1 cm^?1 and they showed a high quantum efficiency for dye sensitization. Under various conditions a linear dependence of the thickness and resistivity of the films on deposition time was observed. The transmission of most of the films was greater than 90%. SnO₂ films with a thickness of more than 500 nm exhibit absorption. The refractive index of these films, as determined by UV-visible interference measurements in reflection, is between 1.8 and 2.2 in the wavelength range 300–860 nm and agrees well with the refractive index determined from interference microscope measurements. Heat treatment of the films exposed to air lowers their conductivity and refractive indices.     

Transport properties of thin SnO2〈Sb〉 films grown by pulsed laser deposition

Thin SnO₂<Sb> films grown by pulsed laser deposition have been characterized by X-ray diffraction, optical spectroscopy, and scanning electron microscopy. The carrier mobility and concentration in the films have been determined as functions of target composition (0–8 at % Sb) using Hall effect measurements, and the resistivity of the films has been measured by a four-probe technique. The lowest resistivity (ρ = 2 × 10^?3 Ω cm) and the highest transmission (? 85%) of the films in the spectral range 400-800 nm have been obtained at a target composition Sb/(Sn + Sb) = 2 at %. The observed variation in the resistivity of the films is determined by changes in carrier concentration to a greater extent than by changes in carrier mobility. X-ray photoelectron spectroscopy results demonstrate that the predominant charge state of the antimony in the films is Sb⁵⁺.     

Photoluminescence of Si<Subscript>0.9</Subscript>Ge<Subscript>0.1</Subscript>O<Subscript>2</Subscript> and GeO<Subscript>2</Subscript> films irradiated with silicon ions

We have studied the photoluminescence (PL) of GeO₂ and 90 mol % SiO₂-10 mol % GeO₂ films synthesized by method of RF magnetron sputtering and then irradiated with silicon ions and annealed. The PL of silicon-implanted GeO₂ films, related to the presence of Si nanocrystals (nc-Si), was observed for the first time. It is established that the transformation of the defect centers responsible for the PL in the spectral range 350–600 nm, as well as the formation of nc-Si emitting in the region of 700–800 nm, significantly depend on the matrix type. In particular, the PL intensity at 700–800 nm in 90 mol % SiO₂-10 mol % GeO₂ films is weak. The role of the isovalent substitution of Si and Ge atoms in the transformation of defect centers and the formation of nc-Si is discussed.     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.     

Properties of stannic oxide thin films produced from the SnCl4-H2O and SnCl4-H2O2 reaction systems

Transparent and conductive stannic oxide films were produced at the relatively low temperature of 250°C from the SnCl₄-H₂O and SnCl₄-H₂O₂ reaction systems by a chemical vapour deposition method. The films were not doped with impurities. Films formed from the first system are superior to those formed from the second with respect to electrical properties although they have a lower deposition rate at the same deposition temperature. The former system gives rise to films with resistivities in the range 10–10^-3 Ω cm between 250 and 400°C. The latter system produces films with resistivities in the range 10²–10^-2 Ω cm between 250 and 450°C. The electrical properties depend on the absorption of hydrogen peroxide as well as on the grain size, which depends on the deposition temperature and the reaction system. The spectral transmissivity for films 0.36–1.1 μm thick varies over the range 80–95% in the regions between 400 and 650 nm for both systems. Different reaction mechanisms take place in different temperature regions for both systems since there are two activation energies in the plot of deposition rate as a function of temperature.     

Electrical and optical properties of indium tin oxide films prepared on plastic substrates by radio frequency magnetron sputtering

The influence of deposition power, thickness and oxygen gas flow rate on electrical and optical properties of indium tin oxide (ITO) films deposited on flexible, transparent substrates, such as polycarbonate (PC) and metallocene cyclo-olefin copolymers (mCOC), at room temperature was studied. The ITO films were prepared by radio frequency magnetron sputtering with the target made by sintering a mixture of 90 wt.% of indium oxide (In₂O₃) and 10 wt.% of tin oxide (SnO₂). The results show that (1) average transmission in the visible range (400-700 nm) was about 85%-90%, and (2) ITO films deposited on glass, PC and mCOC at 100 W without supplying additional oxygen gas had optimum resistivity of 6.35 × 10⁻⁴ Ω-cm, 5.86 × 10⁻⁴ Ω-cm and 6.72 × 10⁻⁴ Ω-cm, respectively. In terms of both electrical and optical properties of indium tin oxide films, the optimum thickness was observed to be 150-300 nm.     

Thermoelectric properties of SiC thick films deposited by thermal plasma physical vapor deposition

SiC thick films of about 300 µm could be prepared with a deposition rate above 300 nm/s by thermal plasma physical vapor deposition (TPPVD) using ultrafine SiC powder as a starting material. The thermoelectric properties were investigated as a function of composition and doping content. The nondoped films showed n-type conduction. Although the Seebeck coefficient reached as high as -480 µV/K, the power factor was only around 1.6 × 10^-4 Wm^-1 K^-2 at 973 K due to the relatively high electrical resistivity. In order to reduce the electrical resistivity and to deposit layers with n-type and p-type conduction, N₂, B and B₄C were selected as the dopants. Nitrogen-doped samples exhibit n-type characterization, B and B₄C-doped samples exhibit p-type characterization, and the electrical resistivity decreased from 10^-2–10^-3 to 10^-4–10^-5 Ωm after doping. The maximum power factor of the nitrogen-doped SiC and the thick films deposited with B₄C powder reached 1.0 × 10^-3 and 6.4 × 10^-4 Wm^-1 K^-2 at 973 K, respectively.

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Analysis of precursors for crystal growth of YBaCuO thin films in magnetron sputtering deposition

We correlated the crystallinity of YBaCuO films prepared by magnetron sputtering deposition using Ar/O₂ mixture gas with the atomic and molecular composition in the gas phase. YBaCuO films were deposited on MgO substrates at 670 °C. Two-dimensional distributions of Y, Ba, Cu, YO, BaO, and CuO densities and one-dimensional distribution of O density were measured by laser-induced fluorescence spectroscopy. The Y and Ba densities decreased significantly with the increase of the O₂ partial pressure, and they were below the detection limit at an O₂ flow ratio of 10% and a total gas pressure of 53 Pa. The decrease in the Y and Ba densities was compensated by an increase in the YO and BaO densities. The decrease in the Cu density with the increase of the O₂ partial pressure was less significant, while the CuO density was below the detection limit at all the discharge conditions. The O density was evaluated to be 10¹²-10¹³ cm^− 3, which was much higher than the Cu density. On the other hand, YBaCuO films with high crystallinity were obtained at total gas pressures of 53-80 Pa and O₂ flow ratios of 50-70%. Therefore, it is concluded that the precursors for the deposition of YBaCuO films with high crystallinity are Cu, YO, BaO, and O.     

Temperature dependence of the microstructure and resistivity of indium zinc oxide films deposited by direct current magnetron reactive sputtering

Indium zinc oxide (IZO) films were deposited as a function of the deposition temperature using a sintered indium zinc oxide target (In₂O₃:ZnO = 90:10 wt.%) by direct current (DC) magnetron reactive sputtering method. The influence of the substrate temperature on the microstructure, surface roughness and electrical properties was studied. With increasing the temperature up to 200 °C, the characteristic properties of amorphous IZO films were improved and the specific resistivity was about 3.4 × 10^− 4 Ω cm. Change of structural properties according to the deposition temperature was also observed with X-ray diffraction patterns, transmission electron microscopy, X-ray photoelectron spectroscopy, and atomic force microscopy. IZO films deposited above 300 °C showed polycrystalline phases evolved on the amorphous IZO layer. Very flat surface roughness could be obtained at lower than 200 °C of the substrate temperature, while surface roughness of the films was increased due to the formation of grains over 300 °C. Consequently, high quality IZO films could be prepared by DC magnetron sputtering with O₂/Ar of 0.03 and deposition temperature in range of 150-200 °C; a specific resistivity of 3.4 × 10^− 4 Ω cm, and the values of peak to valley roughness and root-mean-square roughness are less than 4 nm and 0.5 nm, respectively.     

Physical properties of tin oxide films deposited by oxidation of SnCl2

Highly transparent and conducting SnO₂ films, as required in thin film heterojunction solar cells, were deposited onto Pyrex glass substrates by oxidation of SnCl₂ in the temperature range 350–500°C. Oxygen with a flow rate of between 1 and 3.251 min^-1 was used as both the carrier gas and the oxidizing agent. For films deposited in these conditions the resistivity varies from 10^-2 to 10^-3 Ω cm with transmission in the range 87%–71%. It was observed that both the resistivity and the transmission decrease with increasing deposition temperature. The resistivity of films deposited at a fixed deposition temperature passes through a minimum as the oxygen flow rate is increased. Hence, SnO₂ films with low resistivity and high transmission can be produced by the oxidation of SnCl₂ at relatively low temperatures using the oxygen flow rate corresponding to the minimum resistivity. For example, in the present work, low resistivity (4.4 × 10^-3 Ω cm) and high transmission (87%) were observed for films deposited at 400°C with an oxygen flow rate of 1.81 min^-1. The effects of the deposition temperature, oxygen flow rate and deposition time on the thickness, deposition rate, resistivity and absorption coefficient are discussed in detail.     

Structural evolution of PZTN thin films produced by pulsed laser ablation deposition

The study of highly oriented Nb-doped PZT thin films deposited by laser ablation on n-type (111) Si substrates is reported. Sintered ceramics based on the nominal composition Pb_0.995(Zr_0.65Ti_0.35)_0.99Nb_0.01O₃ (PZTN) with an excess of PbO were used as targets. The films were deposited using the 3rd harmonic (355 nm) of a pulsed Nd:YAG laser (7 ns pulse duration) with 7 J/cm² fluence, at different oxygen pressures (from 10⁻¹ to 10⁻⁴ mbar) and at a vacuum of 10⁻⁶ mbar. The substrate temperature was varied in the range of 500-600 °C. In optimized conditions, the as-deposited PZT-based films show perovskite structure oriented along the (110) direction with minor impurities (PbO), as revealed from X-ray diffraction spectra. Further, microstructural analysis of the as-grown including chemical composition is also presented. The relationship between composition of the target, deposition conditions and film properties are then discussed.     

Effect of composition on mechanical behaviour of diamond-like carbon coatings modified with titanium

In this study, diamond-like carbon (DLC) films modified with titanium were deposited by plasma decomposition of metallorganic precursor, titanium isopropoxide in CH₄/H₂/Ar gas atmosphere. The obtained films were composed of amorphous titanium oxide and nanocrystalline titanium carbide, embedded in an amorphous hydrogenated (a-C:H) matrix. The TiC/TiO₂ ratio in the DLC matrix was found to be dependent on the deposition parameters. The dependence of the films chemical composition on gas mixture and substrate temperature was investigated by X-ray photoelectron spectroscopy, whereas the crystallinity of TiC nanoparticles and their dimension were evaluated by X-ray diffraction. The size of TiC crystallites varied from 10 to 35 nm, depending on the process parameters. The intrinsic hardness of 10-13 GPa, elastic modulus of 170-200 GPa and hardness-to-modulus ratio of obtained coatings were measured by the nanoindentation technique. Obtained results demonstrated a correlation of mechanical properties with the chemical composition and the ratio of amorphous/crystalline phases in the films. In particular, the formation of nanocrystalline TiC with atomic concentration not exceeding 10% and with grain size between 10 nm and 15 nm resulted in significantly enhanced mechanical properties of composite material in comparison with ordinary DLC films.     

Enhanced conductivity of pulsed laser deposited n-InGaZn6O9 films and its rectifying characteristics with p-SiC

Wide band gap InGaZn₆O₉ films of thickness ~ 350 nm were deposited on sapphire (0001) at room temperature by using the pulsed laser deposition technique. The transparent films showed the optical transmission of > 80% with the room temperature Hall mobility of ~ 10 cm²/V s and conductivity of 4 × 10² S/cm at a carrier density > 10²⁰ cm^− 3. The electrical properties as a function of deposition temperatures revealed that the conductivity and mobility almost retained up to the deposition temperature of 200 °C. The films annealed in different atmospheres suggested oxygen vacancy plays an important role in determining the electrical conductivity of the compound. Room temperature grown heterostructure of n-InGaZn₆O₉/p-SiC showed a good rectifying behavior with a leakage current density of less than 10^− 9 A/cm², current rectifying ratio of 10⁵ with a forward turn on voltage ~ 3 V, and a breakdown voltage greater than 32 V.     

Electrical and optical properties of Al-doped ZnO films deposited by hollow cathode gas flow sputtering

Al-doped ZnO (AZO) films were deposited on glass by hollow cathode gas flow sputtering using Zn-Al alloy targets. Sputtering power for all the depositions was fixed at 1500 W. Resistivities of 0.81-1.1 × 10^− 3 Ω cm were obtained for AZO films deposited at room temperature with an O₂ flow from 38 to 50 standard cubic centimetre/minute (SCCM), while static deposition rates were almost constant at 270-300 nm/min. On the other hand, lower resistivities of 5.2-6.4 × 10^− 4 Ω cm were obtained for AZO films deposited at 200 °C with an O₂ flow from 25 to 50 SCCM, while the static deposition rates were almost constant at 200-220 nm/min. Average transmittances in the visible light region were above 80% for both sets of films.     

Temperature dependence of transport properties of evaporated indium tin oxide films

Indium tin oxide films with high conductivity and transparency were successfully prepared by evaporating an alloy of indium and tin covered with In₂O₃ powder. At room temperature the films have high carrier mobilities of about 60 cm² V^-1 s^-1. Conductivities as high as 5 × 10³ Ω^-1 cm^-1 and transmittance values of greater than 90% in the visible region of light were obtained. The carrier mobility was found to be inversely proportional to temperature in the high temperature range and independent of temperature in the low temperature range. The temperature dependence of the carrier conductivity indicated that the carrier excitation energy was less than 8.6 × 10^-6 eV. Mössbauer spectroscopy showed that the tin in all the high quality films was tetravalent.     

Gold films on silicon: Ion-bombardment-induced reactions between gold and silicon

Thin gold films of thickness 80 and 25 nm deposited onto silicon were bombarded with 30 keV Ar⁺ ions to fluences in the range from 4.8 × 10¹⁸ to 1.6 × 10²¹ ions m⁻². Dynamic recoil mixing, i.e. controlled simultaneous deposition of gold and bombardment with Ar⁺ ions, was carried out on gold films 30 nm thick on silicon. All the films were subsequently analysed by Rutherford backscattering spectroscopy, scanning electron microscopy and transmission electron microscopy. The results indicate the formation of a metastable amorphous phase with the composition Au₇₆Si₂₄. The formation of this phase is accompanied by the formation of surface ripples which develop into prominent islands on further ion bombardment. The amorphous phase is stable up to 413 K after which and up to a temperature of 613 K it turns into a stable large-grained polycrystalline compound with a similar composition, and this does not alter on subsequent cooling to room temperature.     

Transparent and heat-reflecting indium tin oxide films prepared by reactive electron beam evaporation

Transparent and heat-reflecting indium tin oxide films were prepared by electron beam evaporation of In₂O₃9mol.%SnO₂ in an oxygen atmosphere of about 5×10^?4 Torr. A visible absorption of less than 2%, a thermal IR reflectance exceeding 90% and a d.c. resistivity of approximately 3×10^?4 Ω cm were obtained from films 0.4 μm thick deposited at a substrate temperature of 300°C. Films with similar properties could be prepared with substrate temperatures as low as 150°C.     

Influence of Fabrication Parameters on Crystallization, Microstructure, Surface Composition, and Optical Behavior of MgO Thin Films Deposited by rf Magnetron Sputtering

In this work MgO thin films have been grown onto common glass substrates by magnetron rf sputtering from a MgO (99.99%) target with dimensions of 4″×¼″. Basically, we found the optimum conditions for deposition such as working pressure (7×10^?3 mbar), the power applied to the target (400 W) and the flow of Ar (20 sccm). The films have been characterized by X-ray diffraction (XRD) at a grazing angle at θ–2θ configuration, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and transmittance studies. The XRD results show that to reproduce the polycrystalline phase of the target, there is a power threshold of 250 W. AFM results indicate that the films present average roughness of the 200 Å and grain size of 1100 Å. XPS shows a surface composition of the films most external 5 nm, indicating the presence of MgO and Mg(OH)₂. The optical characterization indicates that the films have a high absorption coefficient for wavelengths below 310 nm, and between 450 to 850 nm they showed a transmittance average of 90%.     

Growth of nanocrystalline diamond films in CCl4/H2 ambient

We investigated the growth characteristics of the nanocrystalline diamond films using CCl₄/H₂ as gas sources in a hot-filament chemical vapor deposition (CVD) reactor. Successful growth of nanocrystalline diamond at typical growth condition of 1.5-2.5% CCl₄ and 550-730 °C substrate temperature has been demonstrated. Glancing angle X-ray diffraction (XRD) clearly indicated the formation of diamond in the films. Typical root-mean-square surface roughness of 10-15 nm and an optimal root-mean-square surface roughness of 6 nm have been achieved. Transmission electron microscopy (TEM) analyses indicated that nanocrystalline diamond film with an average grain size in the range of 10-20 nm was deposited from 2.5% CCl₄/H₂ at 610 °C. Effects of different source gas composition and substrate temperature on the grain nucleation and grain growth processes, whereby the grain size of the nanocrystalline film could be controlled, were discussed.     

Transparent conducting ZnO thin films deposited by vacuum arc plasma evaporation

A high rate deposition of co-doped ZnO:Ga,F and ZnO-In₂O₃ multicomponent oxide thin films on large area substrates has been attained by a vacuum arc plasma evaporation method using oxide fragments as a low-cost source material. Highly transparent and conductive ZnO:Ga,F and ZnO-In₂O₃ thin films were prepared on low temperature substrates at a deposition rate of approximately 375 nm/min with a cathode plasma power of 10 kW. A resistivity of 4.5×10⁻⁴ Ω cm was obtained in ZnO:Ga,F films deposited at 100 °C using ZnO fragments co-doped with 1 wt.% ZnF₂ and 1 wt.% Ga₂O₃ as the source material. In addition, the stability in acid solution of ZnO films was improved by co-doping. It was found that the Zn/(In+Zn) atomic ratio in the deposited ZnO-In₂O₃ thin films was approximately the same as that in the fragments used. The ZnO-In₂O₃ thin films with a Zn/(In+Zn) atomic ratio of approximately 10-30 at.% deposited on substrates at 100 °C exhibited an amorphous and smooth surface as well as a low resistivity of 3-4×10⁻⁴ Ω cm.