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The concept of an extended Brillouin zone is used to analyze the intensity of phonon modes observed in optical and Raman investigations
of different polytypes of silicon carbide. It is shown that the relative intensity of these modes agrees with the magnitude
of the splitting of the doublets, which are degenerate in the extended zone.
Pis’ma Zh. éksp. Teor. Fiz. 69, No. 3, 247–250 (10 February 1999) 相似文献
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采用平面波超软赝势法和范数不变赝势法对几种SiC多型体的几何结构、能带结构等进行了系统的研究.结果表明:6HSiC导带最低点在ML线上U点,用平面波超软赝势法计算时U点在(0000,0500,0176)点附近;而用范数不变赝势法计算时在导带最低点附近能带呈现不连续点,不连续点出现在(0000,0500,0178)点附近.两种赝势法计算结果相比,用平面波超软赝势法得到的导带最低点位置更靠近布里渊区M(0,05,0)点.在平面波超软赝势下,随着六角度的增加,cp,cpa增大的趋势较为明显,能隙和价带宽度变宽的趋势也较为明显.在计算极限内,绝对零度下4HSiC系统能量最低、最稳定,而Ewald能量显示3CSiC最稳定.
关键词:
密度泛函理论
电子结构
SiC 相似文献
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The electronic band structures of boron nitride crystal modifications of the graphite (h-BN), wurtzite (w-BN), and sphalerite (c-BN) types are calculated using the local coherent potential method in the cluster muffin-tin approximation within the framework of the multiple scattering theory. The specific features of the electronic band structure of 2H, 4H, and 3C boron nitride polytypes are compared with those of experimental x-ray photoelectron, x-ray emission, and K x-ray absorption spectra of boron and nitrogen. The features of the experimental x-ray spectra of boron nitride in different crystal modifications are interpreted. It is demonstrated that the short-wavelength peak revealed in the total densities of states (TDOS) in the boron nitride polytypes under consideration can be assigned to the so-called outer collective band formed by 2p electrons of boron and nitrogen atoms. The inference is made that the decrease observed in the band gap when changing over from wurtzite and sphalerite to hexagonal boron nitride is associated with the change in the coordination number of the components, which, in turn, leads to a change in the energy location of the conduction band bottom in the crystal. 相似文献
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We report an ab initio study of the electronic properties of surface dangling-bond (SDB) states in hydrogen-terminated Si and Ge nanowires with diameters between 1 and 2 nm, Ge/Si nanowire heterostructures, and Si and Ge (111) surfaces. We find that the charge transition levels epsilon(+/-) of SDB states behave as a common energy reference among Si and Ge wires and Si/Ge heterostructures, at 4.3+/-0.1 eV below the vacuum level. Calculations of epsilon(+/-) for isolated atoms indicate that this nearly constant value is a periodic-table atomic property. 相似文献
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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. 相似文献
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Richard Nader Elie Moussaed Michel Kazan Joerg Pezoldt Pierre Masri 《Superlattices and Microstructures》2008,44(2):191-196
Structural and optical measurements were performed on silicon carbide (SiC) samples containing several polytypes. The SiC samples investigated were grown on (111) Si substrates by solid source molecular beam epitaxy (SSMBE). Several quantities of Ge were predeposited before the growth procedure. The influence of Ge on the SiC polytypes formation was studied by X-Ray, FTIR and μ-Raman characterizations methods. The spectra of the samples with less than one Ge monolayer exhibit a mixture of 2H, 15R and 3C–SiC polytypes. This mixture is due to the mismatch between the heterostructure layers. We propose that the Ge predeposition in the heterostructure can be used to stabilize and unify the polytypes formation. 相似文献
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Abstract Lattice parameters for SiC-15R and phonon frequencies for SiC-15R and SiC-6H were investigated as function of pressure by X-ray single crystal analysis and first-order Raman scattering. Linear and bulk moduli and phonon Gruneisen parameters were obtained. Phonon dispersion curves plotted in the standard large zone reveal certain softening of the TA-branch at the zone boundary. The nature of the covalent systems stability is discussed in the light of the sum rule. 相似文献
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V. N. Brudnyi A. V. Kosobutsky 《Journal of Experimental and Theoretical Physics》2012,114(6):1037-1042
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. 相似文献
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Pseudopotential calculations have been carried out for the α, β and γ polytypic forms of the layer semiconductor ZnIn2S4, respectively, corresponding to space groups C53v, C13v and D33d. The required form factors are consistent with those used in our previous calculations for ZnS and CdIn2S4. The band structure of the α phase, the only one up to now for which optical data are available, compares quite satisfyingly with very recent photoemission and reflectivity experimental data. The computed band structures of the β and γ phases are very alike; on the contrary, interesting differences exist between these structures and the α phase which could easily be verified by experimental investigations. 相似文献
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Shang-Peng Gao 《Solid State Communications》2012,152(19):1817-1820
Geometry optimizations are performed for three polytypes of h-BN using density functional theory with dispersion correction for the van der Walls interaction. Quasiparticle band structure calculations are carried out to solve the controversy on band gap type of h-BN. Band energies are corrected by GW method. The h-BN with Bk structure has an indirect band gap of 5.840 eV. Two kinds of h-BN polytypes are shown to be mechanically stable and have quasi-direct band gap type. 相似文献
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Wen-Zhou Chen Qian Li Zhen-Yi Jiang Xiao-dong Zhang Liang Si Li-Sha Li Rui Wu 《Physica B: Condensed Matter》2012,407(14):2744-2748
The structural properties and mechanical stabilities of B2-IrTi have been investigated using first-principle calculations. The elastic constants calculations indicate that the B2-IrTi is unstable to external strain and the softening of C11−C12 triggers the B2-IrTi (cubic) to L10-IrTi (tetragonal) phase transformation. Detailed electronic structure analysis revealed a Jahn–Teller-type band split that could be responsible for elastic softening and structure phase transition. The cubic–tetragonal transition is accompanied by a reduction in the density of states (DOS) at the Fermi level and the d-DOS of Ti at Fermi level plays a decisive role in destabilizing the B2-IrTi phase. 相似文献
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We present the results of theoretical analysis of structural varieties of compounds for which polytypism is important. As a result, the possibility of isomeric polytype varieties existing has been established, as well as regularities in their formation, depending on the period of repeatability of layers in packaging. In addition, the methods of density functional theory are used to calculate the structure and properties of various polytypic modifications of diamond. Dependences of the interlayer distances and the difference total energy on the hexagonality of diamond polytypes and their isomeric varieties have been found. The theoretical powder X-ray diffraction patterns of diamond polytypes are calculated and their comparative analysis is performed. 相似文献
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D. Zhang P. Wang X. Jiao C. Min G. Yuan Y. Deng H. Ming L. Zhang W. Liu 《Applied physics. B, Lasers and optics》2006,85(1):139-143
Optical polarization properties of aluminum, gold and aluminum/gold subwavelength metallic gratings (SWMGs) are investigated numerically in the visible light band. Their performance as polarizing beam splitters are simulated with RCWA for varied metallic materials, grating depth and incident angle. Metallic waveguide theory is applied to explain the performance difference between Au and Al grating. A new type of Al/Au bimetallic is also investigated numerically for potential applications. PACS 42.79.Dj; 42.81.Gs; 73.20.Mf 相似文献
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J. Osvald 《Applied Physics A: Materials Science & Processing》2007,87(4):679-682
We report on a classical approach used to calculate energy band diagrams of AlGaN/GaN heterostructures. We were able to calculate the band diagram and carrier concentrations by this method also when the external bias was applied on the structure. The potential on the Schottky barrier side of the structure is defined more exactly than in a self-consistent solution of Poisson and Schrödinger equations. Dependence of the band profile and the carrier concentration of the two-dimensional gas on the piezoelectric charge can also be calculated by this approach. 相似文献