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。     

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...     

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...     

Polytypism of silicon carbide and Schottky barriers

The results obtained in our previous work [4] are revised taking into account the dependence of the electron affinity on the polytype of silicon carbide SiC. The dependence of the energy level of vacancies in a polytype of silicon carbide on the band gap is determined from the data on the Schottky barrier height and is explained in the framework of a simple two-band model.     

Impurity Effects on Nucleation and Growth of SiC Clusters and Layers on Si(100) and Si(111)

Physics of the Solid State - A kinetic Monte Carlo model of silicon carbide growth on silicon surface is proposed. Based on this model, the growth of silicon carbide clusters on silicon in the...     

Transformation of point defects in silicon dioxide during annealing

In our previous studies, we have demonstrated that annealing of silicon dioxide in the absence of oxygen leads to the formation of silicon clusters near the surface. The mechanism of the formation of silicon clusters by this technique has not been sufficiently investigated. However, it has been found that the rate of the formation of nanoclusters and their sizes depend on the concentration of point defects in the silicon dioxide and on the concentration of impurities, for example, hydroxyl groups. As a continuation of these studies, in the present work we have investigated changes in the concentration of point defects in silicon dioxide films during high-temperature annealing. A new method has been proposed for the evaluation of changes in the concentration of point defects in silicon dioxide films before and after annealing. A model of the transformation of point defects in silicon dioxide into silicon nanoclusters due to the high-temperature annealing has been developed.     

Evolution of the symmetry of intermediate phases and their phonon spectra during the topochemical conversion of silicon into silicon carbide

A symmetry analysis of the crystal structure and the phonon spectrum during continuous topochemical conversion of silicon into silicon carbide has been carried out. The transformation of the symmetry of phonons at high-symmetry points of the Brillouin zone upon the transition from the initial cubic structure of silicon (diamond) through an intermediate cubic structure of silicon carbide to the trigonal structure of SiC has been determined. The selection rules for the infrared and Raman spectra of all the three phases under investigation have been established.     

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.     

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.     

Classification and structure of silicon carbide phases

Molecular-mechanical and semiempirical quantum-mechanical methods have been applied to simulate and calculate a geometrically optimized structure of clusters of polymorphic types of silicon carbide, and their structural parameters and some properties (densities, sublimation energies) have been determined. A classification of silicon carbide phases has been proposed, which shows the possible existence of twenty one SiC phases whose atoms are at crystallographically equivalent sites. The structures of seventeen proposed silicon carbide phases have been described and studied for silicon carbide for the first time.     

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.     

研究SiC多种多型体连生方式的X射线方法

本文提出了一种研究碳化硅多种类型连生的晶体中连生次序的实验方法。用超声波研磨法将极硬的薄片状碳化硅单晶逐层磨薄并逐次摄取双套劳埃照片。对劳埃法得出的SiC多型类型数据的分析可以确定各种连生多型体的次序和比例。用一晶体的实验结果对Mitchell的碳化硅多型性机理作了讨论。     

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.     

Investigation of the 4H-SiC surface

The silicon carbide (SiC) surface is more complex than that of silicon and can be carbon-terminated or silicon-terminated, and can exist as several reconstructions. Investigations of the surface structure as a function of temperature, under ultrahigh vacuum (UHV) conditions using scanning tunneling microscopy (STM) and low energy electron diffraction (LEED), are presented. The 4H-SiC surface can be passivated using a silicon deposition/evaporation technique to reconstruct the surface. This has a significant effect on the electrical behaviour of metal contacts to the silicon carbide surface, critical in any electronic device. Atomic resolution STM studies of the 4H-SiC surface have revealed step features and micropipe defects in unprecedented detail. STM has also been used to image clusters of metal deposited on the 4H-SiC surface. The effect of annealing on the behaviour of these nickel clusters is also presented. The surface of the silicon carbide is extremely important in the fabrication of silicon carbide electronic devices and this paper presents a discussion of the SiC surface with particular reference to its impact on SiC device applications in power electronics.     

Luminescence spectra of hexagonal forms of silicon carbide in mosaic films grown by solid-state epitaxy

The luminescence spectra of silicon carbide films grown on silicon by solid-state epitaxy have been studied. It has been shown that, depending on the growth conditions, one can obtain films of different SiC polytypes, including the cubic and hexagonal ones. In many cases, the films thus grown display a mixture of various polytypes, but it is possible to prepare films of predominantly hexagonal symmetry (the coexistence of the 4H and 2H hexagonal phases, which are close in properties, is also possible). It thus has been demonstrated that the silicon carbide films grown on silicon by solid-state epitaxy are promising for application as damping layers in fabrication of wide-band-gap hexagonal semiconductors on silicon substrates.     

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.     

Features and mechanisms of growth of cubic silicon carbide films on silicon

The mechanisms and specific features of the growth of silicon carbide layers through vacuum chemical epitaxy in the range of growth temperatures from 1000 to 700°C have been considered. The structure of the heterojunction formed has been studied using the results of the performed investigations of photoluminescence spectra in the near-infrared wavelength range and the data obtained from the mass spectrometric analysis. It has been found that, in the silicon layer adjacent to the 3C-SiC/Si heterojunction, the concentration of point defects significantly increases and the dislocation structure is not pronounced. According to the morphological examinations of the surface of the growing film, by analogy with the theory of thermal oxidation of silicon, the theory of carbidization of surface silicon layers has been constructed. A distinctive feature of the model under consideration is the inclusion of the counter diffusion fluxes of silicon atoms from the substrate to the surface of the structure. The growth rate of films and the activation energy of diffusion processes have been estimated. The performed experiments in combination with the developed growth model have explained the aggregates of voids observed in practice under the silicon carbide layer formed in the silicon matrix and the possibility of forming a developed surface morphology (the island growth of films) even under conditions using only one flow of hydrocarbons in the reactor.     

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.     

Negative crystals of silicon carbide

Systems of negative silicon carbide crystals are classified and studied by experimental methods. The crystal structure and morphology forming during growth, etching, and erosion are discussed.     

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.