Influence of the argon flow rate on the arsenic fraction of a-GaxAs1−x sputtered at high substrate temperature

The experimental study of the chemical composition of amorphous gallium arsenide (a-Ga_xAs_1−x) versus argon flow rate, Q, by rf sputtering, shows that the As fraction of sputtered films is controlled by the argon flow rate. At the substrate temperature, T_s=500 °C, the films are stoichiometric when deposited under the argon flow rate between 8 and 22 sccm. These observations indicate that at low argon flow rate the As fraction of films is governed only by the preferential re-sputtering of As during the film growth. In addition, a correlation between the deposition rate R, and chemical composition x was deduced from these results.     

A gradual annealing of amorphous sputtered indium tin oxide: Crystalline structure and electrical characteristics

Thin films of amorphous indium tin oxide were deposited by soft sputtering. The film was gradually annealed in air at temperatures from 110 °C to 150 °C. Its structural and electrical properties were monitored in order to get a better understanding of the annealing process. Firstly, carrier density decreases by oxygen intake. Crystallization speeds up at 150 °C, with a 2.5 D growth of crystallites. The preferred orientations come from sputtering induced seeds. Then, the carrier density increases again due to tin activation. Meanwhile, the carrier mobility is more damaged by the low temperature annealing in air than by a standard annealing in a reducing atmosphere. Thus, tin oxide segregation is suspected at grain boundaries.     

Low temperature (< 100 °C) deposited P-type cuprous oxide thin films: Importance of controlled oxygen and deposition energy

With the emergence of transparent electronics, there has been considerable advancement in n-type transparent semiconducting oxide (TSO) materials, such as ZnO, InGaZnO, and InSnO. Comparatively, the availability of p-type TSO materials is more scarce and the available materials are less mature. The development of p-type semiconductors is one of the key technologies needed to push transparent electronics and systems to the next frontier, particularly for implementing p-n junctions for solar cells and p-type transistors for complementary logic/circuits applications. Cuprous oxide (Cu₂O) is one of the most promising candidates for p-type TSO materials. This paper reports the deposition of Cu₂O thin films without substrate heating using a high deposition rate reactive sputtering technique, called high target utilisation sputtering (HiTUS). This technique allows independent control of the remote plasma density and the ion energy, thus providing finer control of the film properties and microstructure as well as reducing film stress. The effect of deposition parameters, including oxygen flow rate, plasma power and target power, on the properties of Cu₂O films are reported. It is known from previously published work that the formation of pure Cu₂O film is often difficult, due to the more ready formation or co-formation of cupric oxide (CuO). From our investigation, we established two key concurrent criteria needed for attaining Cu₂O thin films (as opposed to CuO or mixed phase CuO/Cu₂O films). First, the oxygen flow rate must be kept low to avoid over-oxidation of Cu₂O to CuO and to ensure a non-oxidised/non-poisoned metallic copper target in the reactive sputtering environment. Secondly, the energy of the sputtered copper species must be kept low as higher reaction energy tends to favour the formation of CuO. The unique design of the HiTUS system enables the provision of a high density of low energy sputtered copper radicals/ions, and when combined with a controlled amount of oxygen, can produce good quality p-type transparent Cu₂O films with electrical resistivity ranging from 10² to 10⁴ Ω-cm, hole mobility of 1-10 cm²/V-s, and optical band-gap of 2.0-2.6 eV. These material properties make this low temperature deposited HiTUS Cu₂O film suitable for fabrication of p-type metal oxide thin film transistors. Furthermore, the capability to deposit Cu₂O films with low film stress at low temperatures on plastic substrates renders this approach favourable for fabrication of flexible p-n junction solar cells.     

Development of higher performance indium tin oxide films at a very low temperature (< 80 °C) by the neutral beam-assisted sputtering process

At very low temperatures (< 80 °C), improved performance indium tin oxide (ITO) thin films with a low resistivity of 4.22 × 10⁻⁴ Ωcm and high transmittance > 90% at 550 nm were developed using the neutral beam-assisted sputtering (NBAS) technique, which included a cyclic inter-treatment process with an Ar neutral beam. Transmission electron microscopy and electron diffraction showed that the neutral particles with hyper-thermal energy was able to enhance the formation of the nano-crystalline phase and activate the dopant without additional heating or plasma damage during ITO thin film deposition.     

Transparent, amorphous and organics-free ZnO thin films produced by chemical solution deposition at 150 °C

We have studied the low-temperature processing of ZnO by chemical solution deposition. A transparent, stable precursor solution prepared from zinc acetate dihydrate dissolved in 2-methoxyethanol was spin-coated on SiO_x/Si, soda-lime glass and polymer substrates and heated at 150 °C. Selected thin films deposited on SiO_x/Si were additionally heated at 450 °C.Microstructural and chemical analyses showed that the thin films heated at 150 °C in air were amorphous, contained no organic residues and had a root mean square roughness of 0.7 nm. The films deposited on SiO_x/Si and heated at 450 °C were crystallised and consisted of randomly oriented grains with a diameter of about 20 nm. All thin films were transparent, exhibiting a transmission of over 80% in the visible range. The resistivity of the 120-nm thick ZnO films processed at 150 °C was 57 MΩ cm and upon heating at 450 °C it decreased to 1.9 kΩ cm.     

Amorphous silicon thin film solar cells deposited entirely by hot-wire chemical vapour deposition at low temperature (< 150 °C)

Amorphous silicon n-i-p solar cells have been fabricated entirely by Hot-Wire Chemical Vapour Deposition (HW-CVD) at low process temperature < 150 °C. A textured-Ag/ZnO back reflector deposited on Corning 1737F by rf magnetron sputtering was used as the substrate. Doped layers with very good conductivity and a very less defective intrinsic a-Si:H layer were used for the cell fabrication. A double n-layer (µc-Si:H/a-Si:H) and µc-Si:H p-layer were used for the cell. In this paper, we report the characterization of these layers and the integration of these layers in a solar cell fabricated at low temperature. An initial efficiency of 4.62% has been achieved for the n-i-p cell deposited at temperatures below 150 °C over glass/Ag/ZnO textured back reflector.     

Low temperature (< 100 °C) fabrication of thin film silicon solar cells by HWCVD

Amorphous silicon films have been made by HWCVD at a very low substrate temperature of ≤ 100 °C (in a dynamic substrate heating mode) without artificial substrate cooling, through a substantial increase of the filament-substrate distance (∼ 80 mm) and using one straight tantalum filament. The material is made at a reasonable deposition rate of 0.11 nm/s. Optimized films made this way have device quality, as confirmed by the photosensitivity of > 10⁵. Furthermore, they possess a low structural disorder, manifested by the small Γ/2 value (half width at half maximum) of the transverse optic (TO) Si-Si vibration peak (at 480 cm^− 1) in the Raman spectrum of ∼ 30.4 cm^− 1, which translates into a bond angle variation of only ∼ 6.4°. The evidence gathered from the studies on the structure of the HWCVD grown film by three different techniques, Raman spectroscopy, spectroscopic ellipsometry and transmission electron microscopy, indicate that we have been able to make a photosensitive material with a structural disorder that is smaller than that expected at such a low deposition temperature.Tested in a p-i-n solar cell on Asahi SnO₂:F coated glass (without ZnO at the back reflector), this i-layer gave an efficiency of 3.4%. To our knowledge, this is the first report of a HWCVD thin film silicon solar cell made at such a low temperature.     

Viscoplastic behavior of a FeCrAl alloy for high temperature steam electrolysis (HTSE) sealing applications between 700 °C and 900 °C

High temperature steam electrolysis (HTSE) is one of the most promising technologies for the industrial production of hydrogen. However one of the remaining problems lies in sealing at high temperature. The reference solution is based on glass seals which presents several drawbacks. That explains why metallic seals are under development. The expected seal will be submitted to creep under low stresses between 700 °C and 900 °C, possibly involving complex loading and thermal history. The candidate material investigated in this work is a FeCrAl (OC404, Sandvik) supplied as a 0.3 mm thick sheet. The ability of this material to develop a protective layer of alumina was studied first, as well as grain size growth during thermal ageing. Creep and tensile tests were performed between 700 °C and 900 °C to determine its mechanical properties. This database was used to propose and identify an elasto-viscoplastic behavior for the material. Creep was described by the Sellars-Tegart law. This law was then used to simulate and predict creep indentation tests performed in the same range of temperatures.     

Effect of 95 °C temperature on the chloride-migration of concrete using electrical field

The effects of 95 °C temperature on the chloride migration (the non-steady-state migration coefficient and the steady-state migration coefficient) of concrete are investigated. The transport properties of control specimens (at room temperature) and heated specimens (at 95 °C temperature) are prepared and studied. In this study the electrochemical technique is applied to accelerate chloride ion migration in concrete to estimate the breakthrough time and the chloride flux. The non-steady-state chloride migration coefficient and the steady-state chloride migration coefficient of concrete are calculated from the modified Fick's second law based on measurements of the breakthrough time and the chloride flux. Sixteen mixes of concrete are tested in this study. The results show that the non-steady-state migration coefficient and the steady-state migration coefficient increase by about 3–11 times and by 3–7 times, respectively, when the temperature is raised from room temperature to 95 °C. It could be assumed that these results are due to the increased connectivity of pores resulting from the increased pores around the interface between aggregate and matrix. The probable increased connectivity of pores at the interfacial transition zone (ITZ) of the specimens could have a major influence on the chloride migration coefficients of concrete.     

Influence of substrate temperature on the electrical and optical properties of amorphous germanium films

The influence of substrate temperature on electrical and optical properties of the amorphous germanium films deposited under well-defined conditions has been investigated. DC electrical conductivity in the temperature range of 80–573°K has been measured. In the low temperature region Mott’sT ^−1/4 law of conductivity is obeyed. The estimated values ofT ₀ andN show significant decrease with change inT _s in steps of 50°K. Similar results are seen in annealed films. The values of activation energy and optical energy increase withT _s.     

Structural and optical properties of amorphous and crystalline antimony sulfide thin-films

Smooth and compact thin films of amorphous and crystalline antimony sulfide (Sb₂S₃) were prepared by radio frequency sputtering of an Sb₂S₃ target. As-deposited films are amorphous. Polycrystalline antimony sulfide films composed of ∼ 500 nm grains are obtained by annealing the as-deposited films at 400 °C in sulfur vapors. Both amorphous and crystalline antimony sulfide have strong absorption coefficients of 1.8 × 10⁵ cm^− 1 at 450 nm and 7.5 × 10⁴ cm^− 1 at 550 nm, and have direct bandgaps with band energies of 2.24 eV and 1.73 eV, respectively. These results suggest the potential use of both amorphous and crystalline antimony sulfide films in various solid state devices.     

Structural and electrical properties of amorphous carbon-sulfur composite films

In this paper, we discuss the synthesis of carbon-sulfur composite (a-C:S) films by vapour phase pyrolysis of maleic anhydride and sulfur. Structural changes in the system are analysed by scanning electron microscopy and powder X-ray diffraction. Microhardness test depicts an increase in the value of hardness with an increase in sulfur concentration. Electrical conductivity of composite samples varies with sulfur concentration. Magnetoresistance (MR) measurements show a drastic increase in the value of MR for the samples prepared at < 900°C. Thermal stability of these samples is analysed by thermogravimetric analysis, which depends on the host structure and the amount of intercalated species.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Effects of composition on optical and electrical properties of amorphous In-Ga-Zn-O films deposited using radio-frequency sputtering with varying O2 gas flows

This study used powders containing various In₂O₃-Ga₂O₃-ZnO (IGZO) chemical compositions to manufacture targets by using a metallurgical process. The resulting targets were used to deposit amorphous In-Ga-Zn-O (a-IGZO) channel films using a radio frequency (r.f.) magnetron sputtering process. The average transmittance increased and achieved saturation; the resistivity increased in conjunction with the O₂ flow ratio of less than 6%; and subsequently, the resistivity decreased with increasing the O₂ flow ratio larger than 6%. This study examined the effects of compositions on electrical characteristics and optical properties of a-IGZO films at varied O₂ flow rates. The effects of composition on optical and electrical characteristics of a-IGZO films indicate that the average transmittance of a-IGZO films with more zinc atoms (approximately 50%) had more than 80% at various O₂ flow ratios because of the higher oxygen absorption of the zinc atoms. However, the average transmittance of a-IGZO film with a lower zinc atomic ratio (approximately 20%) without an O₂ flow ratio decreased to below 10% because of the indium and indium oxide crystalline precipitation in the indium-rich a-IGZO films. The results revealed that the resistivity increased when the gallium atomic ratio increased and the indium atomic ratio decreased.     

Effect of annealing temperature and composition on photoluminescence properties of magnetron sputtered SiCN films

Silicon carbonitride (SiCN) films were prepared by means of reactive magnetron sputtering of a sintered SiC target on n-type Si (1 0 0) substrates in the reactant gas of nitrogen, and then the films were respectively annealed at 600, 800 and 1100 °C for 5 min in nitrogen ambient. The films were characterized by energy dispersive spectrometer, X-ray diffraction, Fourier transform infrared spectroscopy and photoluminescence (PL) spectrophotometry. Intense PL peaks at 370, 400 and 440 nm were observed at room temperature. The results show that annealing temperature and composition play an important role in the structures and PL properties of the films. The annealing temperature of 600 °C favors the formation of the SiC (1 0 9) crystal in the SiCN films, and results in a maximal PL peak. The intensity of the 440 nm PL peak can be improved by increasing the abundance of the Si-C bond.     

Structural,electrical and photoluminescence properties of ZnO:Al films grown on MgO(0 0 1) by direct current magnetron sputtering with the oblique target

ZnO:Al films were deposited on MgO(0 0 1) substrates at 300 K and 673 K by direct current magnetron sputtering with the oblique target. The Ar pressure was adjusted to 0.4 Pa and 1.2 Pa, respectively. All the films have a wurtzite structure and a c-axis orientation in the film growth direction. The films deposited at 300 K initially grow with thin columnar grains and subsequently grow with large granular grains on the thin columnar grains. However, the films grown at 673 K consist mainly of dense columnar grains perpendicular to the substrate surface. The ZnO:Al film deposited at 673 K and 0.4 Pa has the lowest resistivity, the highest free electron concentration and Hall's mobility. A temperature dependence of the resistivity within 5–300 K reveals that the films grown at 300 K exhibit a semiconducting behavior and those grown at 673 K show a metal–semiconductor transition. The carrier transport mechanism is Mott's variable range hopping in the temperature range below 90 K for all the films and thermally activated band conduction above 215 K for the films grown at 300 K. Room temperature photoluminescence spectra for wavelengths between 300 nm and 800 nm reveal mainly blue-green emissions centered at 452 nm, 475 nm and 515 nm.     

Formation of silicon dioxide layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of silicon

The formation of silicon dioxide (SiO₂) layers at low temperatures (150-400 °C) by atmospheric pressure plasma oxidation of Si(0 0 1) wafers have been studied using a gas mixture containing He and O₂. A 150 MHz very high frequency (VHF) power supply was used to generate high-density atomic oxygen in the atmospheric pressure plasma. Oxidation rate, structure, and thickness and refractive index profiles of the oxidized layers were investigated by ellipsometry and infrared absorption spectroscopy. Atomic force microscopy was also employed to observe atomic-scale morphologies of the layer surface and wafer Si surface, after chemical removal of the oxidized layers. It was found that stoichiometric SiO₂ layers were obtained at higher oxidation rates than conventional dry O₂ thermal oxidation and radical oxidation processes, even at a very low substrate temperature of 150 °C. Although thickness variations were observed in the plasma region, the refractive index was independent of both substrate temperature and VHF power. In addition, the SiO₂ surface and SiO₂/Si interface roughnesses were comparable to those obtained in conventional dry oxidation at high temperatures.     

Growth and electrical characterization of Zn-doped InAs and InAs1 − xSbx

The electrical properties of Zn doped InAs and InAsSb layers grown on semi-insulating GaAs by metal organic vapour phase epitaxy, using dimethyl zinc as the p-type dopant source, have been studied. The influence of dopant flow rate, V/III ratio and substrate orientation on the electrical properties of these InAs and InAs_1 − xSb_x layers have been studied at a few appropriate growth temperatures. A promising group V source, tertiary butyl arsenic was used as an alternative to arsenic hydride in the case of InAs growth. The electrical properties of the InAs and InAs_1 − xSb_x epitaxial layers were mainly studied by the Hall effect. However, surface accumulation in these materials results in deceptive Hall results being extracted. A two layer model (assuming the layer to consist of two parallel conducting paths viz. surface and bulk) has therefore been used to extract sensible transport properties. In addition, conventional Hall measurements ignores the high electron to hole mobility ratio in InAs and InAsSb leading to erroneous transport properties.     

Preparation and magnetic properties of SrFeO3−x (x = 0.25 ∼ 0.5) using RF magnetron sputtering optimized through sputtering plasma analysis

We investigated the preparation and the magnetic properties of SrFeO_3−x using conventional RF magnetron sputtering. Photoluminescence spectrum analyses of the sputtering plasma revealed that the film composition was changed even using the stoichiometry target. After fixing the composition of the targets from an intensity ratio of the Sr and Fe plasma, the polycrystalline SrFeO_3−x films with different oxygen deficiencies were able to prepare using the various sputtering gas ratio. The magnetic properties of the samples were also changed with changing the sputtering gas ratio. This magnetic property change was likely due to the suppression of the oxygen deficiency in the film.     

Optical absorption dependence on composition and thickness of InxGa1 − xN (0.05 < × < 0.22) grown on GaN/sapphire

We report the change in optical absorption properties of InGaN epilayers around the critical layer thickness determined from X-ray diffraction. Detrimental sub-band gap absorption is observed in InGaN thin films grown beyond the critical layer thicknesses, and is caused by localized electric fields around extended crystalline defects and aided by V-defects through light channeling. The photoluminescence response from InGaN thin films, grown beyond the critical layer thickness, is reduced owing to absorption of the incident laser light by non-radiative recombination extended crystalline defects. The formation of V-defects is observed to occur beyond the critical layer thickness and continues to grow in areal coverage aiding in sub-band gap absorption. This optical behavior sets constraints to be incorporated in the design of InGaN solar cell and requirement for improvement in epitaxial growth techniques to reduce V-defects.