Paramagnetic defects in diamond films synthesized by the hot filament chemical vapour deposition

Defects in nitrogen‐doped diamond films, produced by hot filament chemical vapour deposition have been studied by Electron Spin Resonance (ESR), Raman spectroscopy and Scanning Electron Microscopy (SEM). The peak‐to‐peak ESR line width (ΔH _pp) varies in the range 0.36‐0.52 mT and depends on the nitrogen concentration in the process gas. In the case of nitrogen‐doped diamond films ESR spectrum shows a hyperfine structure typical of N_S⁰ paramagnetic centre. The shape of the central ESR line shows that it is a superposition of two components: a narrower Lorentzian and a broader Gaussian one, characterized by different saturation behaviour. With increasing nitrogen concentration in process gas the ratio of integral intensities A _G/A _L (Gausian to Lorentzian) of ESR spectrum also increases. The Raman spectra show that with increasing doping level the diamond Raman line at 1332.5 cm^‐1 broadens, the broad band at about 1530 cm^‐1 becomes more pronounced what indicate on degradation of diamond crystallinity and it is in agreement with SEM observation. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis of polycrystalline silicon thin films with ‘icosahedral’ symmetry by ceramics hot wire chemical vapor deposition

We report on synthesis and materials physics of polycrystalline silicon thin films deposited on glass with rarely observed ‘five-fold’ symmetry or ‘icosahedral’ symmetry. We invented these ‘novel form’ of polycrystalline silicon thin films by ceramics hot wire chemical vapor deposition (hot-wire CVD). A new physical effect in hot-wire CVD technology has been proposed that controls the nucleation and growth of silicon thin films on glass substrate.     

Formation of needlelike crystallites during growth of diamond films by chemical vapor deposition

Diamond polycrystalline films have been grown by chemical vapor deposition from a hydrogenmethane mixture. The phase composition and structure of the films were studied using Raman spectroscopy, electron microscopy, and thermogravimetry. It is found that, upon heating in air, the oxidation of the carbon material forming the films occurs at significantly different temperatures, depending on the degree of its order and the crystallite size. This difference is used for selective oxidation of the least ordered fine-grained component of the films. The material obtained by this selective oxidation of the films consists of diamond crystallites shaped like regular micrometer-sized tetragonal pyramids with a radius of tip curvature of several nanometers.     

Structural features of epitaxial NiFe2O4 thin films grown on different substrates by direct liquid injection chemical vapor deposition

NiFe₂O₄ (NFO) thin films are grown on four different substrates, i.e., Lead Zinc Niobate–Lead Titanate (PZN–PT), Lead Magnesium Niobate–Lead Titanate (PMN–PT), MgAl₂O₄ (MAO) and SrTiO₃ (STO), by a direct liquid injection chemical vapor deposition technique (DLI-CVD) under optimum growth conditions where relatively high growth rate (～20 nm/min), smooth surface morphology and high saturation magnetization values in the range of 260–290 emu/ cm³ are obtained. The NFO films with correct stoichiometry (Ni:Fe=1:2) grow epitaxially on all four substrates, as confirmed by energy dispersive X-ray spectroscopy, transmission electron microscopy and x-ray diffraction. While the films on PMN–PT and PZN–PT substrates are partially strained, essentially complete strain relaxation occurs for films grown on MAO and STO. The formations of threading dislocations along with dark diffused contrast areas related to antiphase domains having a different cation ordering are observed on all four substrates. These crystal defects are correlated with lattice mismatch between the film and substrate and result in changes in magnetic properties of the films. Atomic resolution HAADF imaging and EDX line profiles show formation of a sharp interface between the film and the substrate with no inter-diffusion of Pb or other elements across the interface. Antiphase domains are observed to originate at the film–substrate interface.     

Advances in hot wire chemical vapor deposition technology for the synthesis of novel silicon thin films materials

We report in this paper on fabrication of an advanced hot wire chemical vapor deposition technique. We introduced for the first time ‘box-type’ ceramics filament holder in hot-wire CVD technology. The surface topography and atomic-scale structure of the films synthesized by the new ceramics hot-wire CVD technique have been compared with that of films prepared with that of standard hot-wire CVD.     

Predicted nitrogen doping concentrations in silicon carbide epitaxial layers grown by hot-wall chemical vapor deposition

A simple quantitative model for the surface adsorption of nitrogen has been developed to simulate the doping incorporation in intentionally doped 4H–SiC samples during epitaxial growth. Different reaction schemes are necessary for the two faces of SiC. The differences are discussed, and implications to the necessary model adjustments are stressed. The simulations are validated by experimental values for a large number of different process parameters with good agreement.     

Simulation of temperature and gas density field distribution in diamond films growth on silicon wafer by hot filament CVD

In the present study, the temperature and gas density field inside the hot filament chemical vapor deposition (HFCVD) reactor, which play a determinate role on the growth rate and quality of as-deposited diamond films, are simulated using the finite volume method, and the influence of the size and arrangement of filaments and inlets are investigated. Firstly, the correctness of the simulation model is verified by comparing the temperature data obtained from the simulation with that measured in an actual depositing process, and the results show that the error between them is less than 3%. Thereafter, the deposition parameters are optimized using this model as N(filament number)=6, r(filament radius)=0.4 mm, D(filament separation)=16–18 mm, H(substrate–filament distance)=8–9 mm, and 25 inlets. Finally, diamond films are deposited on silicon (100) wafers using above parameters and the results of characterization by SEM and Raman spectrum exhibit that the deposited diamond films appear homogeneous surface with fine-faceted crystals.     

Mechanisms of chemical vapor deposition of silicon

The distribution in the silicon epitaxial growth from SiCl₄ and hydrogen are observed in situ by IR absorption spectroscopy. Two methods are used complementarily, one is IR spectroscopy of reactants extracted from the reactor by a fine quartz tube which is not disturbing the reactions, and gives knowledge about the local distribution, the other is direct IR spectroscopy of hot reactants in the reactor which is useful to ascertain the results at the real high temperature situation. The intermediate species are SiHCl₃, SiH₂Cl₂ which is estimated from the induced emission bands at 500 and 570 cm^-1. HCl is a dominant waste product and contributes to reverse reactions. To investigate the reaction, HCl is intentionally injected into the reacting gas. This kind of injection method may also be very effective to analyze the reactions using other reactants such as SiCl₄, SiHCl₃ and SiH₂Cl₂.     

Low-temperature deposition of crystalline silicon nitride nanoparticles by hot-wire chemical vapor deposition

The nanocrystalline alpha silicon nitride (α-Si₃N₄) was deposited on a silicon substrate by hot-wire chemical vapor deposition at the substrate temperature of 700 °C under 4 and 40 Torr at the wire temperatures of 1430 and 1730 °C, with a gas mixture of SiH₄ and NH₃. The size and density of crystalline nanoparticles on the substrate increased with increasing wire temperature. With increasing reactor pressure, the crystallinity of α-Si₃N₄ nanoparticles increased, but the deposition rate decreased.     

Properties of hydrogenated amorphous silicon prepared by chemical vapor deposition

Properties of hydrogenated amorphous silicon (a-Si:H) prepared by chemical vapor deposition (CVD) are reported and compared to corresponding properties of glow discharge a-Si:H. The CVD material was produced from mixtures of silane, disilane, trisilane and higher polysilanes in hydrogen carrier gas at one atmosphere total pressure, at substrate temperatures from 420 to 530 °C. The photovoltaic properties of our present CVD a-Si:H are somewhat inferior to those of the best glow discharge a-Si:H. However, as discussed below, there are some indications that higher quality CVD a-Si:H may be possible.     

Zn-doped AlInAs grown at high temperature by metalorganic chemical vapor deposition

Zn-doped AlInAs growth at high temperature, mainly at 750°C, by metalorganic chemical vapor deposition is investigated. When introducing DEZn during AlInAs growth, it is necessary to increase the TMAl flow rate in order to make the layer lattice-matched to InP. This is due to the enhanced In incorporation rather than the large covalent radius of Zn. To clarify the electrical characteristics, the dependence of the DEZn flow rate, the V/III ratio, and the growth temperature are investigated using the van der Pauw Hall method. In our growth system, a GaInAs intermediate layer is effective in preventing n-type inversion in Zn-doped AlInAs, which occurs when it is grown directly on an InP buffer layer. In addition, a large DEZn flow rate is effective for reducing carrier compensation in Zn-doped AlInAs layers grown at 750°C. Si impurities are apparently the cause of the type-inversion and compensation in Zn-doped AlInAs.     

Polar dependence of impurity incorporation and yellow luminescence in GaN films grown by metal-organic chemical vapor deposition

We have investigated the unintentional impurities, oxygen and carbon, in GaN films grown on c-plane, r-plane as well as m-plane sapphire by metal-organic chemical vapor deposition. The GaN layer was analyzed by secondary ion mass spectroscopy. The different trend of the incorporation of oxygen and carbon has been explained in the polar (0 0 0 1), nonpolar (1 1 2¯ 0) and semipolar (1 1 2¯ 2) GaN by a combination of the atom bonding structure and the origin direction of the impurities. Furthermore, it has been found that there is a stronger yellow luminescence (YL) in GaN with higher concentration of carbon, suggesting that C-involved defects are originally responsible for the YL.     

Cracking assisted nucleation in chemical vapor deposition of silicon nanoparticles on silicon dioxide

Deposition of sub-monolayer silicon on SiO₂/Si(1 0 0) greatly facilitates nucleation in subsequent thermal chemical vapor deposition (CVD) of silicon nanoparticles. Sub-monolayer seeding is accomplished using silicon atoms generated via disilane decomposition over a hot tungsten filament. The hot-wire process is nonselective towards deposition on silicon and SiO₂, is insensitive to surface temperature below 825 K, and gives controlled coverages well below 1 ML. Thermal CVD of nanoparticles at 1×10⁻⁴ Torr disilane and temperatures ranging from 825 to 925 K was studied over SiO₂/Si(1 0 0) surfaces that had been subjected to predeposition of Si or were bare. Seeding of the SiO₂ surface with as little as 0.01 ML is shown to double the nanoparticle density at 825 K, and densities are increased twenty fold at 875 K after seeding the surface with 30% of a monolayer.     

Low-pressure chemical vapor deposition of TaCN films by pyrolysis of ethylamido-tantalum

Thin films of Tantalum nitride (TaN) were deposited from tetra-ethylamido-tantalum (Ta (NEt₂)₄) by low-pressure chemical vapor deposition. Good-quality step coverage is achieved below 400°C, because the deposition rate is determined by the reaction rates on the surface. The film resistivity increases, however, as the substrate temperature decreases. In order to obtain the low resistivity of films deposited at lower temperatures, we have increased the amount of injected H₂ gas during the deposition. The resistivity decreases by the increase in the H₂ gas flow rate, and it is shown that a large amount of H₂ gas injection during the deposition is an effective method for obtaining both low resistivity and high-quality step coverage. The residual carbon concentration in the film is measured to be >10%, on the other hand, the concentration of N less than 1%. The microstructural investigation using transmission electron microscopy (TEM) reveals that crystalline structure of the deposited film has an amorphous phase.     

Hydrogen removal by annealing from C-doped InGaAs grown on InP by metalorganic chemical vapor deposition

Hydrogen removal from C-doped InGaAs grown on InP substrate by metalorganic chemical vapor deposition is discussed based on the dependence of hole concentration on various annealing conditions. It is revealed that the hydrogen removal rate becomes higher as the annealing temperature is higher and the activation energy of hydrogen removal is about 1.9 eV regardless of C-doped layer thickness. The hydrogen removal rate is also found to be inversely proportional to C-doped layer thickness, suggesting that the hydrogen removal reaction is mainly governed by hydrogen diffusion.     

Nonstoichiometry and nanocrystallization of silicon-rich silicon carbide deposited by chemical vapor deposition

Silicon carbide (SiC) deposited by chemical vapor deposition (CVD) from methyltrichlorosilane (MTS)/H₂ was often found to be silicon-rich and micro- or nanocrystalline. We address here the question whether the excess silicon would be localized inside the small SiC crystals contained in the deposit or not. We performed semi-empirical total energy calculations and free energy estimations which show that excess Si atoms should not be localized inside a finite SiC crystal. This is essentially due to the difference between the Si---Si and Si---C σ overlaps of sp³ hybrids for a given nearest-neighbor distance. Comparison of a crystallographic equation with experimental results from CVD materials suggests that the SiC nanocrystals be of maximum size allowing all excess Si atoms to be localized at the border of the crystals, provided that there are no Si crystals in the deposited material.     

Hydrogenated amorphous silicon produced by laser induced chemical vapor deposition of silane

a-Si:H films deposited by laser induced CVD (LICVD) have been characterized and the growth process modelled. Growth rates are exponentially dependent on gas temperature and film properties follow the equilibrium hydrogen content, exponentially dependent on substrate temperature.     

Optical properties and chemical bonding characteristics of amorphous SiNX:H thin films grown by the plasma enhanced chemical vapor deposition method

Amorphous silicon nitride (SiN_X:H) thin films grown by the plasma enhanced chemical vapor deposition (PECVD) method are presently the most important antireflection coatings for crystalline silicon solar cells. In this work, we investigated the optical properties and chemical bonding characteristics of the amorphous SiN_X:H thin films deposited by PECVD. Silane (SiH₄) and ammonia (NH₃) were used as the reactive precursors. The dependence of the growth rate and refractive index of the SiN_X:H thin films on the SiH₄/NH₃ gas flow ratio was studied. The chemical bonding characteristics and the surface morphologies of the SiN_X:H thin films were studied using the Fourier transform infrared spectroscopy and atomic force microscopy, respectively. We also investigated the effect of rapid thermal processing on the optical properties and surface morphologies of the SiN_X:H thin films. It was found that the rapid thermal processing resulted in a decrease in the thickness, increase in the refractive index, and coarser surfaces for the SiN_X:H thin films.