Electrochemical deposition of Ni and Cu onto monocrystalline n-Si(100) wafers and into nanopores in Si/SiO2 template

Nickel and copper were potentiostatically deposited onto monocrystalline n-Si (100) wafers and in nanoporous SiO₂/Si template from 0.5 M NiSO₄ + 0.5 M H₃BO₃ and 0.005 M CuSO₄ + 0.5 M H₃BO₃ solutions. Nanoporous SiO₂/Si template was formed by etching in dilute HF solution of ion tracks. The latter were produced by high-energy (380 MeV) Au⁺ ions bombardment of silicon oxide thermally grown on silicon (100) substrate. The deposition of metals was studied using cyclic voltammetry (CV), chronoamperometry; the structure and morphology of products were ex-situ investigated by SEM and XRD. The level of pores filling was controlled by deposition time. Electrodeposition occurred selectively into nanopores and the deposition on SiO₂ layer was excluded. It was found out that Ni and Cu electrodeposited into nanopores of SiO₂/Si system formed the same structures as at electrodeposition on the surface of monocrystalline n-Si—granules for Ni and scale-shaped particles for Cu deposits.     

Properties of silicon nitride films prepared by plasma-enhanced chemical vapour deposition of SiH4-N2 mixtures

The refractive indices and IR absorption spectra are measured for silicon nitride films plasma deposited from SiH₄-N₂-H₂ gas mixtures. The composition of the film (N:Si ratio) is derived from the value of the refractive index and the concentration of bonded hydrogen as Si-H and N-H in the film is estimated from the absorption intensities in the IR spectrum. The optimum deposition conditions for giving excellent insulating silicon nitride films are confirmed to be same as the conditions for giving films with stoichoimetric composition and the lowest amount of incorporated hydrogen.     

Sources of Carbon Impurities in the Preparation of High-Purity Monoisotopic <Superscript>28</Superscript>Si by a Hydride Method

This paper examines sources of carbon impurities in polycrystalline monoisotopic ²⁸Si prepared by a hydride method. Analytical data on the concentrations of carbon-containing impurities in volatile silicon compounds (²⁸SiH₄ and ²⁸SiH₄), process gases (Ar and H₂), and polycrystalline ²⁸Si are used to identify the major sources of carbon in the polycrystalline ²⁸Si prepared by the hydride method. These are the starting ²⁸SiH₄ and calcium hydride used in ²⁸SiH₄ conversion into ²⁸SiH₄. The rate of carbon intake into polycrystalline silicon from the apparatus material during the monosilane pyrolysis process does not exceed 9 × 10¹¹ cm^–2 h^–1. Polycrystalline silicon has been precipitated from monosilane with different concentrations of hydrocarbon impurities. At hydrocarbon concentrations in the range 10^–4 to 10^–3 mol %, the carbon concentration in the monosilane correlates with that in the silicon obtained from it. High-purity monosilane has been used to prepare polycrystalline ²⁸Si samples with concentrations of carbon impurities in the range (0.8–2.3) × 10¹⁵ cm^–3. Based on calculations of the carbon impurity distribution along the length of a zone-refined ingot, we examine the effect of the initial carbon concentration in the starting polycrystal on the yield of single-crystal monoisotopic ²⁸Si. Requirements are formulated for the carbon concentration in polycrystalline ²⁸Si which ensure a high yield of single crystals with parameters suitable for metrological applications.     

Optical property and crystalline quarity of Si and Ge added β-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> thin films

A transparent electrode of β-Ga₂O₃ films for solar cells, flat panel displays and other devices, which consist in chemically abundant and ecological elements of gallium and oxygen, were grown on quartz or silicon substrates by RF magnetron sputtering using a sintered Ga₂O₃ target. The impurities of Si or Ge were also added into the grown films. The polycrystalline β-Ga₂O₃ grew by the thermal annealing after RF sputtering. Optical absorption measurements indicated that the grown β-Ga₂O₃ film after 600°C annealing have a band gap of about 5 eV.     

Growth and characterisation of wide-bandgap,I-VII optoelectronic materials on silicon

γ-CuCl is a wide-bandgap (E_g = 3.395 eV), direct bandgap, semiconductor material with a cubic zincblende lattice structure. Its lattice constant, a_CuCl = 0.541 nm, means that the lattice mismatch to Si (a_Si = 0.543 nm) is < 0.5%. γ-CuCl on Si—the growth of a wide-bandgap, direct bandgap, optoelectronics material on silicon substrates is a novel material system, with compatibility to current Si based electronic/optoelectronics technologies.The authors report on early investigations consisting of the growth of polycrystalline, CuCl thin films with layer thicknesses of 100 nm to 1 μm on Si (100), Si (111), and quartz substrates by physical vapour deposition. X-ray diffraction (XRD) studies indicate that CuCl grows preferentially in the (111) direction but an epitaxial alignment with the substrate is also detected to a lesser extent in the case of Si (100). Photoluminescence (PL) and Cathodoluminescence (CL) reveal a strong room temperature Z₃ excitonic emission at ≈387 nm. X-ray microanalysis and XRD are used to investigate the effect of heat treatments on the CuCl thin films after deposition in the temperature range of 50 to 430∘C, (melting point of CuCl ≈ 430∘C). It is a found that a reaction occurs with Si on heating above 250∘C forming SiCl₄ and Cu.     

Surface and optical characterization of the porous silicon textured surface

In the present studies, the structural and optical properties of the electrochemically etched PS layers are presented. The formation conditions under constant anodization current density was varied to get a variety of PS samples to analyze the structural and optical characteristics of the porous silicon layers and, then to correlate the resultant surface morphology with the etching process. The low-porosity PS layers thus formed on the silicon substrate have a refractive index value (n_ps = 1.9), which is an intermediate value between bulk silicon substrate (n_Si = 3.4) and air (n_air = 1.0). The results of diffused reflectance, surface morphology by atomic force microscopy (AFM), and Raman scattering measurements show that the resultant surface morphology of the PS layers consist of irregular and randomly distributed nanocrystalline Si structures. The reduction in reflection of the low porosity porous silicon layers is due to light scattering and light trapping of the incoming light by total randomization of the incoming light within the PS structure. The Fourier transform infrared (FTIR) measurements on the PS layer on Si substrate show that PS surface is characterized by chemical species like Si—H and Si—O etc., co-existing on the surface. The presence of hydrogen-related species on the PS layer can provide to some extent a surface passivation effect.     

Features of formation of germanium silicate glasses during oxidation of nanostructured films of germanium-doped polycrystalline silicon

Nanostructured films of polycrystalline silicon obtained by joint pyrolysis of monosilane (SiH₄) and monogermane (GeH₄) were oxidized in a medium of dry and wet oxygen. As a result of their oxidation, vitreous films of complex oxides of germanium and silicon, germanium silicate glass (GSG), is formed. It is established that the presence of germanium in the composition of nanostructured films of polycrystalline silicon (NSF PCS) increases their reaction ability with respect to oxidation. Using the methods of IR spectroscopy, XPE spectroscopy, Auger spectroscopy, and thermal analysis, the composition and phase transformation of vitreous oxides formed in the course of oxidation of NSF PCS are investigated. It is shown that the composition and phase transformation of the films of vitreous silicon and germanium oxides depend on the germanium content in the NSF PCS and conditions of their oxidation.     

Structure and optical properties of Zr1−xSixN thin films on sapphire

A series of zirconium silicon nitride (Zr_1−xSi_xN) thin films were grown on r-plane sapphire substrates using reactive RF magnetron co-sputtering of Zr and Si targets in a N₂/Ar plasma. X-ray diffraction pole figure analysis, X-ray reflectivity, X-ray photoelectron spectroscopy (XPS), optical microscopy, and optical absorption spectroscopy were used to characterize the film stoichiometries and structures after growth at 200 °C and post-deposition annealing up to 1000 °C in ultra-high vacuum. The atomically clean r-plane sapphire substrates induce high quality (100) heteroepitaxy of ZrN films rather than the (111) orientation observed on steel and silicon substrates, but the addition of Si yields amorphous films at the 200 °C growth temperature. After the annealing treatment, films with Si content x < 0.15 have compressive stress and crystallize into a polycrystalline structure with (100) fiber texture. For x > 0.15, the films are amorphous and remain so even after ultra-high vacuum annealing at 1000 °C. XPS spectra indicate that the bonding changes from covalent to more ionic in character as Si―N bonds form instead of Zr―N bonds. X-ray reflectivity, atomic force microscopy (AFM) and optical microscopy data reveal that after post-deposition annealing the 100 nm thick films have an average roughness < 2 nm, except for Si content near x = 0.15 corresponding to where the film becomes amorphous rather than being polycrystalline. At this stoichiometry, evidence was found for regions of film delamination and hillock formation, which is presumably driven by strain at the interface between the film and sapphire substrate. UV-visible absorption spectra also were found to depend on the film stoichiometry. For the amorphous Si-rich films (x > 0.15), the optical band gap increases with Si content, whereas for Zr-rich films (x < 0.15), there is no band gap and the films are highly conductive.     

High-temperature thermal conductivity of biomorphic SiC/Si ceramics

Thermal conductivity of biomorphic SiC/Si, a silicon carbide + silicon containing two phase material, was evaluated using the laser steady-state heat flux method. These materials were processed via silicon melt infiltration of wood-derived carbon scaffolds. In this approach, heat flux was measured through the thickness when one side of the specimen was heated with a 10.6-µm CO₂ laser. A thin mullite layer was applied to the heated surface to ensure absorption and minimize reflection losses, as well as to ensure a consistent emissivity to facilitate radiative loss corrections. The influence of the mullite layer was accounted for in the thermal conductivity calculations. The effect of microstructure and composition (inherited from the wood carbonaceous performs) on measured conductivity was evaluated. To establish a baseline for comparison, a dense, commercially available sintered SiC ceramic was also evaluated. It was observed that at a given temperature, thermal conductivity falls between that of single-crystal silicon and fine-grained polycrystalline SiC and can be rationalized in terms of the SiC volume fraction in biomorphic SiC/Si material.     

RF sputtered piezoelectric zinc oxide thin film for transducer applications

This paper demonstrates the substrate dependency of the c-axis zinc oxide growth in radio-frequency sputtering system. Different deposition conditions were designed to study the influences of Si, SiO₂/Si, Au/Ti/Si, and Au/Ti/SiO₂/Si substrates on the piezoelectric and crystalline qualities of the ZnO thin films. Experimental results showed that the multilayer of Au/Ti/SiO₂/Si-coated silicon substrate provided a surface that facilitated the growth of ZnO thin film with the most preferred crystalline orientation. The 1.5 μm-thick thermally grown amorphous silicon dioxide layer effectively masked the crystalline surface of the silicon substrate, thus allowing the depositions of high-quality 20 nm-thick titanium adhesion layer followed by 150 nm-thick of gold thin film. The gold-coated surface allowed deposition of highly columnar ZnO polycrystalline structures. It was also demonstrated that by lowering the deposition rate at the start of sputtering by lowering RF power to less than one-third of the targeted RF power, a fine ZnO seed layer could be created for subsequent higher-rate deposition. This two-step deposition method resulted in substantially enhanced ZnO film quality compared to single-step approach. The influence of stress relaxation by annealing was also investigated and was found to be effective in releasing most of the residual stress in this layered structure.     

Binding energies of Si 2<Emphasis Type="Italic">p</Emphasis> and Co 3<Emphasis Type="Italic">p</Emphasis> electrons in cobalt silicides

The binding energies of Si 2p and Co 3p core-shell electrons in four stable cobalt silicides (Co₃Si, Co₂Si, CoSi, and CoSi₂) have been determined by high-resolution photoelectron spectroscopy using synchrotron radiation. The silicides were formed by solid-state epitaxy under identical conditions on Si(100), Si(110), and Si(111) faces of silicon single crystals.     

NMR,XRD, IR and synchrotron NEXAFS spectroscopic studies of OPC and OPC/slag cement paste hydrates

This work aims to determine the fundamental similarities and/or differences between OPC and OPC/slag paste hydrates. OPC and 35% slag pastes are investigated using five techniques: ²⁹Si NMR, ²⁷Al NMR, X-ray diffraction (XRD), infrared (IR) and synchrotron near edge X-ray absorption fine structure (NEXAFS) spectroscopy. ²⁹Si NMR provides valuable information related to the formation of the C–S–H gel, the main hydrated phase of the cement paste. ²⁷Al NMR is a useful tool to characterize calcium aluminates and aluminate hydrates such as ettringite and monosulphate hydrate. XRD identifies polycrystalline phases of the hardened cement paste, including ettringite, monosulphate and CaOH₂. Vibrational frequencies in IR assist in identifying the silicate, sulphate and carbonate phases of the cement paste. As far as we are aware, Si K-edge NEXAFS has never been applied in cement research and its advantages and disadvantages are discussed. Using these techniques, a comparison between OPC and 35% slag paste hydrates is made, shedding light on differences in the amount and form of hydrated phases present, especially the absence of ettringite in the 35% slag paste.     

L'oxynitrure de silicium: Si2N2O I. Attribution des absorptions du spectre infrarouge aux vibrations fondamentales

Infrared absorption frequencies (4000 ? 200 cm^?1) are assigned to stretching and bending normal vibrations of the various inter-atomic bonds in silicon oxinitride. The two kinds of atoms linked to the silicon with different force constants as well as numerous results on the Si1bO1bSi bridge in materials with quite the same symmetry make Si₂N₂O a suitable material for such an investigation. The study of silicon oxygen bonds is more particulary supported by the analysis of vibrations in a “pseudo-molecule” (N₃Si1bO1bSiN₃), with a simplified computation of valence force field, and by their correlation with normal modes in the primitive cell. The assigment is also supported by a study using internal coordinates of the reduced representation of the degrees of freedom and by the behavior of the absorption bands at low temperature.     

The Extended Range of Reaction-layer Fatigue Susceptibility of Polycrystalline Silicon Thin Films

A linear elastic fracture mechanics analysis of a silicon dioxide-polycrystalline silicon (SiO₂–Si) bimaterial system was performed to assess the vulnerability of micron-scale silicon structures, such as microelectromechanical systems, to fatigue in ambient air. Previous research has shown that fatigue of silicon films is due to a “reaction-layer fatigue” process where silicon structural films fail due to the sequential, mechanically induced thickening and environmentally assisted cracking of the silicon dioxide reaction layer which forms on the surface upon exposure to air. This work specifically considered the stability of a crack reaching the SiO₂–Si interface. This analysis revealed a significant overestimate in the oxide thicknesses susceptible to reaction-layer fatigue reported in our previous studies. Instead, a surface oxide layer as thin as 15 nm may activate this fatigue mechanism for a polycrystalline silicon thin film whose fracture strength exceeds 5 GPa.     

SiNx/a-SiCx:H passivation layers for p- and n-type crystalline silicon wafers

In this work we present a detailed investigation of Si surface passivation obtained by a PECVD double dielectric layer, composed of intrinsic hydrogenated amorphous silicon-carbon (a-SiC_x:H), followed by a silicon nitride (SiN_x). The double layers have been deposited on p- and n-type of mono- and multi-crystalline silicon wafers. IR spectra have been carried out to evaluate the structure of a-SiC_x:H layers on monocrystalline wafers. The passivation effects have been studied performing the following measurements: the photoconductance decay, to measure contactlessly the effective lifetime of passived mono and multi Si wafers; the capacitance voltage profile of Al/SiN_x/Si, Al/a-SiC_x:H/Si and Al/SiN_x/a-SiC_x:H/Si MIS structures, to estimate the field effect at the dielectric/silicon interface and individuate the passivation mechanism on silicon surfaces. It has been found that the mechanism of the surface passivation depends on the doping type of the silicon wafer. Indeed from C-V measurements it has been realized that the great amount of positive charge within the SiN_x is able to promote an inversion layer if it is deposited on a-SiC_x:H/Si p-type and an accumulation if it is grown on a-SiC_x:H/Si n-type.     

Optoelectronic properties n:CdS:In/p-Si heterojunction photodetector

Optoelectronic properties of CdS:In/Si anisotype heterojunction photodetector fabricated by depositing of polycrystalline CdS and indium doped CdS films used thermal resistive technique on clean monocrystalline p-type silicon substrates are presented. The effect of In diffusion temperature(T _d)in CdS layer on the optoelectronic characteristics of these devices has been studied. Two peaks situated at 650 and 800 nm with values of 0.32 and 0.43 A/W, respectively, were observed in the responsivity plot. Other optoelectronics properties such as detectivity, photovoltaic, and response time are also presented.     

IR and x-ray studies of ion-beam-synthesized aluminium nitride films

IR transmission spectroscopy in conjunction with X-ray diffraction was used to characterize the phase composition of aluminium films after nitrogen ion implantation. Aluminium films deposited onto single-crystal silicon and implanted with 30 keV nitrogen ions (¹⁴N₂⁺) to a dose of 10¹⁷-10¹⁸ ions cm^-2 were subsequently characterized for aluminium nitride (AIN) formation by IR spectroscopy. The formation of a stoichiometric AIN layer was evident from the IR absorption band observed at 648 cm^-1. Furthermore, X-ray diffraction of an aluminium foil after nitrogen implantation at 110 keV to a dose of 5.0 × 10¹⁷ ions cm^-2 on each side revealed the presence of a polycrystalline AIN phase. A thermal treatment at 700°C did not yield any new crystalline phases.     

Structural, morphological and optical properties of TiO2 films prepared using aqueous sol–gel methods

The influence of the preparation conditions on the structural, morphological and optical properties of TiO₂ thin films deposited on silicon substrate (Si), indium tin oxide coated glass (ITO) and alkali-free borosilicate glass (AFG), respectively is studied in this work. The X-ray diffraction analysis revealed that all TiO₂ samples had a polycrystalline structure. The TiO₂ films coated on Si showed a mixed phase of anatase and rutile while in the case of those on ITO and AFG only the pure anatase phase was observed. The crystallite size within the TiO₂ thin films varied with the calcinations temperature, solvent lateral chain and catalyst type. The optical transmittance, band gap, reflective index and porosity were strongly affected by the annealing temperature, substrate nature and solvent.     

Magnetron sputter deposition of (SiC)<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>(AlN)<Subscript>x</Subscript> solid solution films

Magnetron sputtering of polycrystalline SiC-AlN targets was used to obtain films of (SiC)_{1− x} (AlN)_x solid solutions on silicon carbide (6H-SiC) substrates heated to a temperature in the range T = 500–1200°C. The deposits were characterized with respect to structure, composition, and optical absorption. It is demonstrated that the films obtained on 6H-SiC substrates at T ≥ 1000°C possess a single crystal structure. The compositions of (SiC)_1−x (AlN)_x films are close to those of the corresponding SiC-AlN targets.     

Infrared light emission from porous silicon

Very intense broad sub-bandgap infrared (IR) light emission around 1,550 nm was observed on porous silicon by photoluminescence (PL) measurements. The integrated intensity of the IR signal is two orders of magnitude higher than that of the band–band emission in Cz silicon. PL measurements with the sample immersed in different media, e.g., in HF and H₂O₂, confirmed that the broad IR band originates from the Si/SiO _x interface. Electroluminescence spectroscopy was carried out on a porous silicon p–n junction sample contacted with indium-tin oxide. The IR band was detected at room temperature at both forward and reverse bias. The results indicate that radiative recombination through interface states is very efficient at room temperature.