Determination of size and concentration of critical clusters of silicon carbide in the vapour phase in homogeneous nucleation process

The concentrations of clusters of various size in the atmosphere during silicon carbide crystal growth have been calculated on the basis of fundamental ideas of homogeneous nucleation theory, taking into account the specific parameters of silicon carbide. It has been shown that the cluster concentration are sufficiently high to conclude that this is the dominant influence during the initial stages of crystal growth. In this way the assumption of the polymer theory of polytypism, namely that the polytype properties of silicon carbide can be determined from the composition of the gas phase, containing sufficiently large clusters with various polytype structures, has been confirmed.     

碳化硅多型体连生现象的X射线研究

本工作用劳埃法对分布于三十二炉的四百多个碳化硅单晶进行了类型分布、连生规律和结构完整性等的分析。大量的观察表明,碳化硅片状晶体中的共轴平行连生是一种普遍的现象,二种以上类型的连生占晶体总数的三分之二。文中列出了各种连生类型的统计。系统地报导了SiC晶体连生状况的X射线法实验结果。对各炉晶体所作的类型分布的分析表明,不同的制备条件下影响较大的是颜色和结构完整度。类型分布的规律性并不明显,邻近的晶体类型可以完全相异。用实验数据分析了类型、颜色和蚀坑间的关系。对碳化硅多型体产生的机理作了讨论。     

Structural heteroepitaxy during topochemical transformation of silicon to silicon carbide

Silicon carbide samples synthesized from silicon by topochemical substitution of atoms are studied by the ion channeling method. The results of the analysis unambiguously demonstrate the occurrence of structural heteroepitaxy. The lattice of synthesized silicon carbide of hexagonal polytype 6H is epitaxially matched in the 〈0001〉 direction with the lattice grating grid array network of an initial substrate silicon in the 〈111〉 direction. The main features of structural self-coupling matching in this epitaxial heterocomposite are revealed. Despite the very large silicon carbide and silicon lattice parameter mismatch, the misfit dislocation density at the interface is low, which is a feature of the topochemical substitution method leading to comparable structures.     

Synthesis of α -SiC nanocrystals by carbothermal reduction of spherical nanoparticles of amorphous silicon dioxide

The method for carbothermal reduction of spherical particles of amorphous silicon dioxide is developed, and hexagonal α-SiC polytype nanocrystals are synthesized. The prepared samples are characterized by X-ray diffraction, Raman spectroscopy, photoluminescence spectroscopy, and electron microscopy. The silicon carbide nanocrystals prepared have sizes in the range 5–50 nm depending on the diameter of initial silicon dioxide particles. A detailed analysis of the positions of the lines in the Raman spectra, their broadening, and shift makes it possible to reliably establish that the samples under investigation predominantly contain the 6H and 4H silicon carbide polytypes and insignificant amounts of the 2H and 3C phases. The 15R and 21R polytypes in the samples are absent. It is noted that the samples are characterized by a substantial size effect: the luminescence intensity of small silicon carbide nanocrystals is more than three times higher than that of large SiC nanocrystals.     

On the calculation of the linear and quadratic dielectric susceptibilities of hexagonal silicon carbide

The electron and lattice contributions to the linear and quadratic dielectric susceptibilities of the hexagonal polytype of silicon carbide 2H-SiC are calculated within the Harrison bond-orbital model. The results obtained are in satisfactory agreement with the calculations performed by other authors and are close in order of magnitude to the corresponding values for the 6H-SiC polytype.     

High-Temperature Spin Manipulation on Color Centers in Rhombic Silicon Carbide Polytype 21R-SiC

JETP Letters - A family of atomic-scale color centers, the spin state of which can be controlled via optical and microwave channels, has been found in the rhombic polytype of silicon carbide...     

Asymmetric split-vacancy defects in SiC polytypes: a combined theoretical and electron spin resonance study

Transition metal defects were studied in different polytypes of silicon carbide (SiC) by ab initio supercell calculations. We found asymmetric split-vacancy (ASV) complexes for these defects that preferentially form at only one site in hexagonal polytypes, and they may not be detectable at all in cubic polytype. Electron spin resonance study demonstrates the existence of ASV complex in niobium doped 4H polytype of SiC.     

Techniques for Polytypic Transformations in Silicon Carbide

Physics of the Solid State - Two main polytype transformations in silicon carbide, namely, 2H → 6H and 3C → 6H, have been studied by ab initio methods. It has been shown that the...     

Electronic structure and spatial distribution of the spin density of shallow nitrogen donors in the SiC lattice

The discovery of unique magnetooptical properties of paramagnetic centers in silicon carbide, which make it possible to control spins of small arrays of centers of atomic sizes to single centers at room temperatures, using the techniques of optical detection of the magnetic resonance, posed a number of problems, among which one of the main ones is the creation of conditions under which spin relaxation effects are minimized. As studies of properties of spin nitrogen-vacancy centers in diamond showed, the main contribution to spin relaxation is made by the interaction with nitrogen donors, being a major impurity in diamond. A similar problem exists for silicon carbide, since nitrogen donors are also basic background impurities. The objective of this work is to study the spatial distribution of the spin density of nitrogen donors in two basic silicon carbide polytypes, i.e., 4H-SiC and 6H-SiC, to use this information for minimizing the interaction of nitrogen donors with paramagnetic centers in silicon carbide. The results of the study are analyzed by magnetic resonance methods; the spin density distribution on the nearest coordination spheres of nitrogen donors occupying carbon sites in silicon carbide is determined. It is concluded that paramagnetic centers in the 4H-SiC polytype, including silicon vacancies, can be more stable to the interactions with unpaired donor electrons, since electrons are not localized on the coordination sphere closest to the paramagnetic center in this case.     

Effect of inelastic deformation on crystallite size in post-shock 6H polytype SiC

Shock-recovery experiments have been conducted on 6H polytype silicon carbide to 135 GPa and post-shock samples have been analyzed by Raman spectroscopy, x-ray diffraction, and electron microscopy. Results indicate that at up to 25-30 GPa, crystallite size is reduced faster than above this pressure, when reduction slows. Shock-induced inelastic deformation of 6H-SiC is known to develop fully for stress above 25 GPa, coinciding with the pressure range observed where crystallite size reduction decreases. Inelastic deformation appears to be responsible for this slowed crystallite size reduction.     

Monte Carlo study of the hetero-polytypical growth of cubic on hexagonal silicon carbide polytypes

In this article we use three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on misoriented hexagonal (4H and 6H) substrates. We analyze the quality of the 3C-SiC film varying the polytype, the miscut angle and the initial surface morphology of the substrate. We find that the use of 6H misoriented (4°–10° off) substrates, with step bunched surfaces, can strongly improve the quality of the cubic epitaxial film whereas the 3C/4H growth is affected by the generation of dislocations, due to the incommensurable periodicity of the 3C (3) and the 4H (4) polytypes. For these reasons, a proper pre-growth treatment of 6H misoriented substrates can be the key for the growth of high quality, twin free, 3C-SiC films.     

4H-SiC纳米薄膜的微结构及其光电性质研究

采用新设计的电极结构的等离子体增强化学气相沉积(PECVD)技术,在高功率密度、高氢稀释比、低温、偏压及低反应气压的条件下,在衬底表面形成双等离子流,增加了衬底表面SiC的成核概率,增强成核作用,形成纳米晶.采用高H2等离子体刻蚀弱的、扭曲的、非晶Si—C及Si—Si和Si—H等键时,由于H等离子体对纳米SiC晶粒与非晶态键的差异刻蚀作用,产生自组织生长,发生晶化.Raman光谱和透射电子衍射(TEM)的测试结果表明,纳米晶SiC是4HSiC多型结构.电子显微照片表明平均粒径为16nm,形状为微柱体.实验结果指出,SiC纳米晶的形成必须经过偏压预处理成核,并且其晶化存在一个功率密度阈值;当低于这一功率密度阈值时,晶化消失;当超过这一阈值时,纳米晶含量随功率密度的提高而增加.随着晶化作用的加强,电导率增加. 关键词： 4H-SiC PECVD 纳米结构 多型薄膜 纳米电子学     

Estimates of the spontaneous polarization in silicon carbide

Various approaches to calculating the spontaneous polarization P _sp for different polytypes of silicon carbide are discussed. Our estimates combined with data reported by other authors reveal a considerable scatter in the values of P _sp for the 2H-SiC polytype (from ?1.11 to ?4.32 × 10^?2 C/m²). The need for further studies is stressed.     

Electronic structure and the local electroneutrality level of SiC polytypes from quasiparticle calculations within the GW approximation

The most important interband transitions and the local charge neutrality level (CNL) in silicon carbide polytypes 3C-SiC and nH-SiC (n = 2?C8) are calculated using the GW approximation for the self energy of quasiparticles. The calculated values of band gap E _g for various polytypes fall in the range 2.38 eV (3C-SiC)-3.33 eV (2H-SiC) and are very close to the experimental data (2.42?C3.33 eV). The quasiparticle corrections to E _g determined by DFT-LDA calculations (about 1.1 eV) are almost independent of the crystal structure of a polytype. The positions of CNL in various polytypes are found to be almost the same, and the change in CNL correlates weakly with the change in E _g, which increases with the hexagonality of SiC. The calculated value of CNL varies from 1.74 eV in polytype 3C-SiC to 1.81 eV in 4H-SiC.     

Some features of surface formation during brittle failure of covalent crystals with diamond-type lattice according to EPR data

The dependence was found of the intensity of “mechanical paramagnetic centres” EPR signals on the temperature of grinding of diamond, silicon carbide, silicon and germanium crystals. Signals intensity increase with grinding temperature lowering (up to 77 K) is related with formation of the materials' amorphous phase during their brittle failure as well as with specific features of the microcracks structure development.     

Thermodynamic study of the solubility process of boron in silicon carbide,grown from the vapour phase

The thermodynamics of the solubility process of the acceptor impurity boron in silicon carbide is investigated. The thermodynamic analysis of equilibrium in the Si-C-B system has been carried out and the temperature dependences of the partial pressures of interacting components are determined for the temperature interval (1800–3000) K.The calculation of the Fermi level in p-SiC(B) is carried out. The heat of solution and the distribution coefficient of boron in silicon carbide are determined on the basis of the thermodynamic analysis of the Si-C-B system, the experimental temperature dependence of boron solubility and the calculation of the Fermi level and Fermi-Dirac distribution in p-SiC(B).     

The possibility of cyclotron echo generation in graphene on a SiC substrate

The possibility of cyclotron echo generation in graphene on a silicon carbide substrate has been predicted on the basis of the direct quasi-classical Monte Carlo simulation. The nature of this effect is the quasi-relativistic dependence of the effective mass of charge carriers on their velocity. The numerical values of the field strengths at which the effect should be most pronounced are found.     

宽带隙薄膜材料场电子发射研究的背景、现状和问题

介绍了以金刚石为代表的宽带隙薄膜材料场电子发射研究背景和现状,对金刚石、类金刚石（ＤＬＣ）、立方氮化硼（ｃ－ＢＮ）、氮化铝（Ａ１Ｎ）和碳化硅（ＳｉＣ）薄膜场电子发射研究的进展进行了评述,着重介绍了发射性能与薄膜的结构特征、杂质含量和处理方法间的关系,并讨论了研究中存在的问题。     

pH-Dependent shape changes of water-soluble CdS nanoparticles

Annealing of silicon-carbon nanoparticles was performed in argon at atmospheric pressure to enable formation of silicon carbide nanomaterials and/or carbon structures. Three precursor powders with increasing crystallinity and annealing temperatures from 1,900 to 2,600 °C were used to gain information about the effect of precursor properties (e.g. amorphous vs. nanocrystalline, carbon content) and annealing temperature on the produced materials. Three structures were found after annealing, i.e. silicon carbide crystals, carbon sheets and spherical carbon particles. The produced SiC crystals consisted of several polytypes. Low annealing temperature and increasing crystallinity of the precursor promoted the formation of the 3C-SiC polytype. Raman analysis indicated the presence of single-layer, undoped graphene in the sheets. The spherical carbon particles consisted of curved carbon layers growing from the amorphous Si–C core and forming a ‘nanoflower’ with a diameter below 60 nm. To our knowledge, the formation of this kind of structures has not been reported previously. The core was visible in transmission electron microscopy analysis at the annealing temperature of 1,900 °C, decreased in size with increasing temperature and disappeared above an annealing temperature of 2,200 °C. With increasing crystallinity of the precursor material, fewer layers (~5 with the most crystalline precursor) were detected in the carbon nanoflowers. The method presented opens up the possibility to produce new carbon nanostructures whose properties can be controlled by changing the properties of the precursor material or by adjusting an annealing temperature.     

Preparation and application of the 3C–SiC substrate to piezoelectric micro cantilever transducers

This study examines the fabrication process and mechanical properties of piezoelectric films with the substrate, which is made from silicon carbide. After depositing the PZT thick film on silicon carbide substrate and silicon substrate respectively, it was shown that silicon carbide substrate formed a stable interface with PZT thick film up to 950?°C, compared with silicon substrate. In addition, the dielectric constant of the PZT thick film sintered at 950?°C on a silicon carbide substrate was 843, and this value was about over 25 % improved value compared with that on a silicon substrate. A thick film piezoelectric micro transducer of a micro cantilever type was fabricated by using a multifunctional 3C–SiC substrate. The fabricated micro cantilever was a micro cantilever with multiple thin films on either silicon or silicon carbide substrate. The piezoelectric thick-film micro cantilever that was fabricated by using a SiC substrate showed excellent mechanical and thermal properties. The piezoelectric micro cantilever on the SiC substrate shows an excellent sensitivity towards the change of mass compared with the piezoelectric micro cantilever on the Si substrate.