Hexagonal Polytypes Research Articles

Characterization of nano-bio silicon carbide

Plasma-enhanced chemical vapor deposition, reactive magnetron sputtering, hot-wire chemical vapor deposition and radio frequency plasma-enhanced chemical vapor deposition were used to develop technology for preparation of nano-bio silicon carbide coating of ceramic materials for dental applications. The effect of the bias voltage applied to the ceramic prostheses and dental crowns on the crystallization processes have been recognized. The optimal bias voltage applied to conductive substrate was –200 V, whereas for dielectric substrate the bias voltage Vbias did not affect the properties of SiC coating. The analysis of CVCs and spectroscopic diagnostics as the methods for studying the mechanism of interfacial rearrangements to investigate SiC phase transition in nano silicon carbide coatings were used. The conductivity of the SiC coating coincided with the conductivity on the dielectric (µn0 = 1012…1013 сm–1·s–1·V–1). The conductive substrate had a significant effect on the properties of the coating and thus depended on the bias voltage Vbias. The conductivity increased by three-four orders of magnitude (µn0 = 3·1017 сm–1·s–1·V–1), if the bias voltage Vbias = –200 V. The increase of the bias voltage (Vbias = –600 V) led to a decrease in the conductivity (µn0 = 1011…1012 сm–1·s–1·V–1). It was found that there was the double injection regime with bimolecular recombination in this structure with the dependence I = V3/2 for CVCs of SiC. The luminescence spectrum of SiC coating on non-dielectric ceramics (if Vbias = – 200 V during deposition) was significantly different from the luminescence spectrum of SiC coating on dielectric ceramics. Increasing the applied voltage to the substrate Vbias during deposition led to increasing the fraction of hexagonal polytypes. Directions in the crystal lattice according to the photoluminescence spectra were identified from the comparing the values of the width of the non-phonon parts of stacking faults and deep level spectra in the low-temperature photoluminescence with arrangements of atoms in the SiC lattice structure. The displacement of each atom participating in photoluminescence allowed to find the correlation with technology of SiC deposition and to develop technology of SiC coating on the dental materials.

Comparative Ellipsometric Analysis of Silicon Carbide Polytypes 4H, 15R, and 6H Produced by a Modified Lely Method in the Same Growth Process

A model is suggested for a quantitative analysis of the dependence of the dielectric function of hexagonal silicon carbide polytypes on photon energy in the range of 0.7–6.5 eV. The model, which is the sum of two Tauc–Lorentz oscillators (main and minor) with a common energy gap, is used to describe three hexagonal silicon carbide polytypes (4H, 15R, 6H) obtained in the same growth process. Both C- and Si-faces of each polytype are analyzed. A number of conclusions are drawn about how the oscillator parameters depend on the degree of hexagonality of a polytype and on the type of a surface face. The strongest dependence is that the amplitude of the minor oscillator grows with increasing degree of hexagonality of a polytype. The increase in the energy gap on passing from the C-face (000 $$\bar {1}$$ ) to the Si-face (0001) is also worthy of note.

Unraveling crystal symmetry and strain effects on electronic band structures of SiC polytypes

The modulations of the electronic band structures of hexagonal (2H, 4H, and 6H) and cubic (3C) SiC under biaxial (0001) and (111) in-plane strain are investigated by using first-principles calculations including spin–orbit coupling effects. We have clarified that the strain dependency of the valence bands is closely related to the crystal symmetry and hexagonality. Specifically, tensile strain induces hybridization and crossover between the heavy-hole and light-hole bands in the hexagonal polytypes. On the other hand, the degeneracy between the heavy-hole and light-hole bands breaks in the cubic polytype under tensile strain. Consequently, the hole effective masses change significantly under certain tensile strain in all four polytypes. The values of the critical tensile strain are approximately proportional to the energy differences between the heavy-hole and crystal-field splitting bands under no strain and, in turn, show a correlation with the hexagonality. In contrast to the case of the valence bands, the band structures around the conduction band minima and, therefore, the electron effective masses are insensitive to the strain, except for the ML direction in 6H–SiC. The present study provides principles for elucidating and designing the crystal structure and strain dependency of the electronic band structures and transport properties of SiC.

Evolution of Structure, Magnetism, and Critical Behavior of Nanocrystalline BaCo1-yMnyO3-δ (0.0 ≤ Y ≤ 0.3)

We report the structural, magnetic, and magnetocaloric properties of the nanocrystalline BaCo1-yMnyO3-δ (0 ≤ y ≤ 0.3) samples synthesized by sol-gel method. The samples crystallized into different hexagonal polytypes as a function of composition and annealing temperature. The crystal structure of parent BaCoO3 (y = 0) changed from 2H- to mixed 2H+10H (y = 0.3) through 2H+12H (y = 0.2) hexagonal phase for 900 °C annealed samples. The increase in annealing temperature reduces the fraction of face sharing octahedra, and the crystal structure of 1100 °C samples exhibited 2H+12H, 12H, 12H+10H, and 2H+10H- hexagonal phases. The relationship between structural and magnetic properties is explained by the structural spin model projection. The 2H- and 10H-hexagonal phases exhibited antiferromagnetic ordering, whereas 12H- phase attributed to ferrimagnetic ordering. The critical exponent analysis indicates that the 12H- hexagonal phase exhibits mean-field approach and the other mixed hexagonal polytypes do not follow any universal model.

Impact of polytypism on the ground state properties of zinc oxide: A first-principles study

The last past two decades have witnessed tremendous scientific and technological interest in zinc-oxide (ZnO), a wide-band gap II-VI semiconductor with unparalleled optoelectronic, piezoelectric, thermal and transport properties. Herein, we present a clear view of the electronic structure properties of cubic (3C), hexagonal (2H, 4H, and 6H) and body-centered tetragonal polytypes of ZnO using stat-of-the-art first-principles pseudopotentials method.All the crystal structures studied evince marked energetic stabilities, rivaling with the ground-state wurtzite 2H phase. Furthermore, the calculations of the elastic constants and phonon dispersion evidence the mechanical and dynamical stabilities of the four ZnO-polymorphs. In addition, the impact of the stacking order on the structural, energetic, electronic, piezoelectric, and dynamical properties is explored and examined.

Self-ordering water molecules at TiO2 interfaces: Advances in structural classification.

In the five-decade search for efficient photocatalysts to convert natural sunlight into hydrogen via photoelectrochemical (PEC) dissociation of water, the underlying physics and chemistry of PEC processes taking place at metal-oxide photocatalysts remains relatively poorly understood and is an active area of research by both theorists and experimentalists. This is surely the case for water structuring at metal-oxide surfaces, including their "self-ordering." In this work, we apply classical molecular-dynamics techniques to investigate and classify the structure and ordering of water layers at two TiO2 surfaces-anatase ⟨101⟩ and rutile ⟨110⟩. We are interested in identifying and classifying layers using local order parameters to distinguish the layered-water superstructure from bulk-like water configurations as observed in liquid water and common ice polymorphs. In particular, we look for the formation of regions with reduced molecular mobility and assess whether they are "ice-like," as has been proposed in recent interpretations in the literature, or, instead, how these interfacial-water structures might be otherwise described. We leverage quantitative and order-parameter analysis techniques to categorize the structural properties of layers of water molecules formed and compare them to both cubic and hexagonal polytypes of bulk ice I, as well as bulk liquid water. In doing so, we propose a general structural recognition/classification framework suitable for identifying and describing molecules at any condensed-state-water interface.

Generation of empirical pseudopotentials for transport applications and their application to group IV materials

Empirical pseudopotentials (EPs) allow for accurate and efficient modeling of atomistic electron transport. Unfortunately, EPs are available only for a few materials and atomic configurations. Furthermore, EPs for nanostructures have historically been described using a variety of different parameterized forms. To compete with more general first-principles methods, we propose an automated workflow to generate EPs of a general form for any material and atomistic configuration. In particular, we focus on the generation of EPs for electron transport calculations, i.e., we provide an EP that accurately reproduces a reference band structure. To demonstrate the applicability of the proposed method, we generate the EPs to reproduce the band structure for bulk Si, Ge, 3C–SiC (zinc-blende polytype), 4H–SiC (hexagonal polytype), diamond, and hydrogen terminated ⟨100⟩ oriented Si and Ge thin films, calculated using first principles. In addition, using the generated EPs, along with the virtual crystal approximation, we demonstrate that our method reproduces accurately the band structure related properties of Si1−xGex alloy as a function of Ge mole fraction, x. As an application of our generated EPs, we perform ballistic quantum transport simulations of extremely scaled (≈0.6 nm wide), hydrogen terminated, ⟨100⟩ oriented Ge and Si gate-all-around nanowire field-effect transistors and compare their transfer characteristics.

Synthesis and characterization of molybdenum disulfide nanoparticles in Shewanella oneidensis MR-1 biofilms.

Shewanella oneidensis MR-1 is a dissimilatory metal-reducing bacterium capable of reducing various metal and sulfur compounds and precipitating them in nanoparticulate form. Here, we report the synthesis of molybdenum disulfide nanomaterials at the site of S. oneidensis biofilms grown in the presence of molybdenum trioxide and sodium thiosulfate. Samples from the growth medium were imaged using scanning electron microscopy and characterized using transmission electron microscopy, energy-dispersive x-ray spectroscopy, absorbance spectroscopy, and x-ray diffraction. These methods revealed the presence of molybdenum disulfide nanoparticle aggregates 50-300 nm in diameter with both hexagonal and rhombohedral polytypes. As a biosynthesis method for molybdenum sulfide, the use of S. oneidensis offers the advantage of significantly reduced heat and chemical solvent input compared to conventional methods of synthesizing molybdenum disulfide nanoparticles.

A theoretical and experimental study of hexagonal molybdenum trioxide as dual-ion electrode for rechargeable magnesium battery

Abstract The hexagonal polytype of molybdenum trioxide (h-MoO3) was prepared through the hydrothermal method. The anisotropic growth of the particles yields to micro rods with prismatic geometry. Theoretical calculations were carried out to simulate the insertion of magnesium in the framework of h-MoO3. The electrochemical behavior of single-phase h-MoO3 in non-aqueous magnesium cells was studied, and for that purpose, Mg metal or activated carbon (A.C.) was used as a counter electrode. This is the first report about the insertion of a divalent cation into h-MoO3. The experimental capacity vs. Mg is only around 20–50 mAh g−1. Nevertheless, whether Mg metal is replaced by A.C. as the counter electrode, the electrochemical behavior of h-MoO3 is improved, and the reversible capacity is about 100 mAh g−1 after 130 cycles. The combination of h-MoO3 and A.C. forms a hybrid or asymmetric electrochemical capacitor. The mechanism of the reaction in the working electrode is more complex than a Mg2+-insertion. Anion (TFSI−) adsorption and redox of oxygen ions in the lattice of h-MoO3 also contribute to the reversible capacity. Consequently, h-MoO3 is a dual-ion electrode material. For higher mass ratio A.C./h-MoO3, the experimental maximum reversible capacity is up to 350 mAh g−1 (equivalent to nominal composition Mg0.94MoO3).

Degradation mechanisms in mixed-cation and mixed-halide CsxFA1−xPb(BryI1−y)3 perovskite films under ambient conditions

With in situ ESEM and GIWAXS we saw that the perovskite degradation passes through hexagonal polytypes and is dependent on the composition.

Сравнительный эллипсометрический анализ политипов карбида кремния 4H, 15R, 6H, полученных модифицированным методом Лели в одном ростовом процессе

In this paper, we propose a model for the quantitative analysis of the dependence of the dielectric function of hexagonal silicon carbide polytypes on the photon energy in the range 0.0–6.5 eV. This model consists of the sum of two Tauc-Lorentz oscillators (main and minor) with a total band gap. This approach is used to describe the three hexagonal polytypes of silicon carbide 4H, 15R, 6H obtained in one growth process. Both C-faces and Si-faces of each polytype are analyzed. A number of conclusions have been made about the dependence of the oscillator parameters on the polytype hexagonality degree and the type of surface face. The strongest dependence is an increase of the minor oscillator amplitude with an increase of polytype hexagonality degree. It should also be noted that the band gap increases upon transition from the C-face (0001 ̅) to the Si-face (0001).

Fabrication of Gas-Sensor Chips Based on Silicon–Carbon Films Obtained by Electrochemical Deposition

In this study, we designed two types of gas-sensor chips with silicon–carbon film, doped with CuO, as the sensitive layer. The first type of gas-sensor chip consists of an Al2O3 substrate with a conductive chromium sublayer of ~10 nm thickness and 200 Ω/□ surface resistance, deposited by magnetron sputtering. The second type was fabricated via the electrochemical deposition of a silicon–carbon film onto a dielectric substrate with copper electrodes formed by photoelectrochemical etching. The gas sensors are sensitive to the presence of CO and CH4 impurities in the air at operating temperatures above 150 °C, and demonstrated p- (type-1) and n-type (type-2) conductivity. The type-1 gas sensor showed fast response and recovery time but low sensitivity, while the type-2 sensor was characterized by high sensitivity but longer response and recovery time. The silicon–carbon films were characterized by the presence of the hexagonal 6H SiC polytype with the impurities of the rhombohedral 15 R SiC phase. XRD analysis revealed the presence of a CuO phase.

Nanoscale mapping of chemical composition in organic-inorganic hybrid perovskite films.

Lead-based organic-inorganic hybrid perovskite (OIHP) solar cells can attain efficiencies over 20%. However, the impact of ion mobility and/or organic depletion, structural changes, and segregation under operating conditions urge for decisive and more accurate investigations. Hence, the development of analytical tools for accessing the grain-to-grain OIHP chemistry is of great relevance. Here, we used synchrotron infrared nanospectroscopy (nano-FTIR) to map individual nanograins in OIHP films. Our results reveal a spatial heterogeneity of the vibrational activity associated to the nanoscale chemical diversity of isolated grains. It was possible to map the chemistry of individual grains in CsFAMA [Cs0.05FA0.79MA0.16Pb(I0.83Br0.17)3] and FAMA [FA0.83MA0.17Pb(I0.83Br0.17)3] films, with information on their local composition. Nanograins with stronger nano-FTIR activity in CsFAMA and FAMA films can be assigned to PbI2 and hexagonal polytype phases, respectively. The analysis herein can be extended to any OIHP films where organic cation depletion/accumulation can be used as a chemical label to study composition.

Comparative Studies on Structural Properties and Total Energetics of Nonequivalent Hexagonal Polytypes for a Wide Variety of Metallic Systems

Since the functionalities of materials usually originate from the spatial inhomogeneity in the associated systems, the local inhomogeneity such as defect, surface, interface, and nanostructure often assumes an important role for developing sophisticated materials. In this paper, among the many phenomena related to inhomogeneity in materials, we will report our computational research on the phenomenon called "Polytypism". Polytypism is a special case of polymorphism when the two polymorphs differ only in the stacking of identical two-dimensional sheets or layers. The polytypes are characterized by a stacking sequence with a given repeating unit along a directional axis (c-axis) and are theoretically possible to have endless permutations of the sequences. Among these polytypes, the crystalline systems composed of close-packed (CP) layers have especially attracted attention on their fundamental and technological properties for many years. While these polytypes are often experimentally observed in wide-bandgap semiconductors, SiC is particularly known to show several hundred polytypes [1]. In addition, the long period stacking ordered (LPSO) Mg alloys with light weight, high specific strength, and high heat resistance are also recently drawing attention as a metallic system with similar polytypism to that in SiC [2]. We have proposed a computational method coupled with three theoretical tools (PGA: polytype generation algorithm; FPC-DFT: first-principles calculations based on the density functional theory; and ANNNI: axial next-nearest-neighbor Ising model), which can make us possible to efficiently investigate the structural energetics for diverse nonequivalent polytypes [1]. In the present study, also motivated by the recent research activities on the LPSO [2], we have systematically evaluated the static energetics of metallic polytypes for a wide variety of elements based on the same computational method proposed by the authors [1]. For all these elemental systems, the atomistic geometry, energetics, and electronic structure for all polytypes with up to the periodic stacking length of L=13 (165 kinds of polytypes in total) have been carefully calculated based on the DFT within the GGA. Using the ANNNI model extracted from the GGA calculations, some trends of physical properties will be illustrated for the tremendous kinds of nonequivalent stacking polytypes based on the efficient PGA. In the CP structures, three different layers are often denoted by A, B, and C, corresponding to different atomistic positions in the planes perpendicular to the stacking direction (c-axis). These descriptions for nearest neighbor stacking result in the so called “hk” notation, where a letter “h” is assigned to each layer with the same type of layer at both sides (e.g., AXA, BXB, CXC) and a letter “k” is assigned otherwise. Using this “hk” notation, the “hexagonality”(σH ) is essentially defined as σH=nh/(nh+nk), where nh and nk are numbers of layers in a hexagonal or cubic environment, respectively [1]. Figure 1 exemplifies the increments of (a) lattice constants in the basal plane (a-axis) and (b) total energies as a function of hexagonality for the nonequivalent polytypes composed of Be, Mg, Pd, and Pt within the present GGA calculations. The figure implies that both physical values are depicted based on those in the 3C (fcc) configuration. We have found that these values have a strong linear correlation with hexagonality in the polytypes for any elemental systems except for La with 4H ground state. The rate of change of both physical values with respect to hexagonality in Mg is found to be significantly smaller than those in other elemental systems. Therefore, the trend should be key factors for the formation of stacking faults, twin boundaries, and also LPSO structures experimentally observed in Mg-based alloys [2]. Focusing on Fig.1 (a), it should be noticed that the a-axis lattice constant decreases with increasing hexagonality in the elemental systems with 3C (fcc) ground state and the opposite trend is true in the systems with 2H (hcp) ground state. Kaneko et al. have experimentally reported that the property of oxygen reduction reaction (ORR) on the catalytic Pt surface is maximized with a 2.0% surface compression strain [3]. Since the compression ratio of lattice constant against hexagonality can be reached around 1.5% in Pt system, the ORR performance may be sufficiently influenced by the stacking faults and/or twin boundaries in the vicinity of surface. Therefore, control of the polytypism in metallic systems may provide interesting functionalities of materials in various fields of solid-state science. [1] K. Moriguchi, et al., J. Mater. Res. 28, 7 (2013) and references therein.[2] E. Abe et al., Phil. Mag. Lett, 91, 690 (2011). [3] S. Kaneko et al., J. Phys. Chem. Lett, 8, 5360 (2017). Figure 1

Co-deposition of diamond and β-SiC by microwave plasma CVD in H2-CH4-SiH4 gas mixtures

The co-deposition of diamond and silicon carbide (SiC) was realized in a microwave plasma using H2-CH4-SiH4 mixtures at enhanced microwave power density of up to 150 W/cm3, and SiC/diamond composite films on (100) Si substrates were produced. The growth parameters were selected to ensure almost equal deposition rates of ~0.3 μm/h for both phases. Composite films were formed either directly on Si surface, or on a buffer (nucleation) layer of SiC or diamond, preliminary deposited on the Si substrate. The film structure has been characterized by SEM, XRD, Raman and PL spectroscopy. It was confirmed that the silicon carbide phase in the composite is the cubic polytype β-SiC (3C-SiC) with the presence of only a small fraction of the hexagonal polytype, while the diamond is in well-faceted microcrystalline form. Diamond grains are Si-doped as was evidenced by the strong photoluminescence of silicon-vacancy color centers. Also, minor inclusions of amorphous sp2 carbon and of trans-polyacetylene (t-PA) were detected in the β-SiC phase. The overall crystalline quality of the composite is high, as evidenced by narrow Raman peaks both for diamond and β-SiC. Our results show, that with an appropriate choice of growth parameters, particularly SiH4/CH4 ratio, high-quality films of Si-doped diamond, silicon carbide, SiC-diamond composite, and combinations of these structures can be synthesized in a single process. Prime novelty statementThe co-deposition of diamond and SiC was realized by microwave plasma CVD using H2-CH4-SiH4 mixtures at enhanced microwave power density; β-SiC/diamond composite films were produced with high crystalline quality on (100) Si substrates.

Manipulating the Mixed-Perovskite Crystallization Pathway Unveiled by In Situ GIWAXS.

Mixed perovskites have achieved substantial successes in boosting solar cell efficiency, but the complicated perovskite crystal formation pathway remains mysterious. Here, the detailed crystallization process of mixed perovskites (FA0.83 MA0.17 Pb(I0.83 Br0.17 )3 ) during spin-coating is revealed by in situ grazing-incidence wide-angle X-ray scattering measurements, and three phase-formation stages are identified: I) precursor solution; II) hexagonal δ-phase (2H); and III) complex phases including hexagonal polytypes (4H, 6H), MAI-PbI2 -DMSO intermediate phases, and perovskite α-phase. The correlated device performance and ex situ characterizations suggest the existence of an "annealing window" covering the duration of stage II. The spin-coated film should be annealed within the annealing window to avoid the formation of hexagonal polytypes during the perovskite crystallization process, thus achieving a good device performance. Remarkably, the crystallization pathway can be manipulated by incorporating Cs+ ions in mixed perovskites. Combined with density functional theory calculations, the perovskite system with sufficient Cs+ will bypass the formation of secondary phases in stage III by promoting the formation of α-phase both kinetically and thermodynamically, thereby significantly extending the annealing window. This study provides underlying reasons of the time sensitivity of fabricating mixed-perovskite devices and insightful guidelines for manipulating the perovskite crystallization pathways toward higher performance.

Strain engineering of core–shell silicon carbide nanowires for mechanical and piezoresistive characterizations

This study evaluated the mechanical properties and piezoresistivity of core–shell silicon carbide nanowires (C/S-SiCNWs) synthesized by a vapor–liquid–solid technique, which are a promising material for harsh environmental micro electromechanical systems (MEMS) applications. The C/S-SiCNWs were composed of a crystalline cubic (3C) SiC core wrapped by an amorphous silicon dioxide (SiOx) shell; however, TEM observations of the NWs showed that hexagonal polytypes (2H, 4H , and 6H) were partially induced in the core by a stacking fault owing to a Shockley partial dislocation. The stress–strain relationship of the C/S-SiCNWs and SiC cores without an SiOx shell was examined using MEMS-based nanotensile tests. The tensile strengths of the C/S-SiCNWs and SiC cores were 7.0 GPa and 22.4 GPa on average, respectively. The lower strength of the C/S-SiCNWs could be attributed to the SiOx shell with the surface roughness as the breaking point. The Young’s modulus of the C/S-SiCNWs was 247.2 GPa on average, whereas that of the SiC cores had a large value with scatter data ranging from 450 to 580 GPa. The geometrical model of the SiC core based on the transmission electron microscopy observations rationalized this scatter data by the volume content of the stacking fault in the core. The piezoresistive effects of the C/S-SiCNW and SiC core were also evaluated from the I–V characteristics under uniaxial tensile strain. The gauge factor of –30.7 at 0.008 ε for the C/S-SiCNW was approximately two-times larger than that of –15.8 at 0.01 ε for the SiC core. This could be caused by an increase of the surface state density at the SiOx/SiC interface owing to the positive fixed oxide charge of the SiOx shell.

Impact of Crystal Types of AgFeO2 Nanoparticles on the Peroxymonosulfate Activation in the Water.

A simple co-precipitation method was developed to synthesize AgFeO2 nanoparticles (NPs) with hexagonal 2H and 3R polytypes coexistence. The ratio of 2H and 3R types in AgFeO2 NPs were regulated by controlling the calcination temperature (300, 400, and 500 °C). Such AgFeO2 NPs were used as heterogeneous catalysts to activate peroxymonosulfate (PMS) for the removal of Orange I (OI) in the water. External water conditions effects and the stability of AgFeO2 NPs were investigated. The catalytic performance of AgFeO2 NPs was found to be significantly enhanced with the increasing content of 2H-AgFeO2. 1O2, O2•-, SO4•-, and •OH were identified as the dominating reactive oxygen species (ROSs) participated in the catalytic process. The electron transfer of Ag0/Ag+ and Fe2+/Fe3+ cycles facilitated the decomposition of PMS to generate ROSs. The surface hydroxyl groups (-OH) were regarded as the catalytic active sites. The higher 2H-AgFeO2 content in AgFeO2 NPs promoted the concentration of surface hydroxyl groups ( C-OH) and the reactivity of AgFeO2 NPs for PMS activation. Based on theoretical calculations, the 2H-AgFeO2 (004) plane with more Fe sites was more conducive to binding with the -OH compared to the 3R-AgFeO2 (012) plane, ascribed to the stronger adsorption energy and shorter Fe-O bond length between 2H-AgFeO2 and -OH.

Radiation Defects in Heterostructures 3C-SiC/4H-SiC

The effect of 8 MeV proton irradiation on n-3C-SiC epitaxial layers grown by sublimation on semi-insulating 4H-SiC substrates has been studied. Changes in sample parameters were recorded using the Hall-effect method and judged from photoluminescence spectra. It was found that the carrier removal rate (Vd) in 3C-SiC is ~100 cm−1, which is close to Vd in 4H-SiC. Compared with 4H and 6H silicon carbide, no significant increase in the intensity of the so-called defect-related photoluminescence was observed. An assumption is made that radiation-induced compensation processes in 3C-SiC are affected by structural defects (twin boundaries), which are always present in epitaxial cubic silicon carbide layers grown on substrates of the hexagonal polytypes.

SiC nanodot formation in amorphous-Si and poly-Si substrates using a hot-C+-ion implantation technique

We experimentally studied SiC nanodot formation in an amorphous-Si (a-Si) and poly-Si on quartz substrates, using a hot-C+-ion implantation technique and post-N2 annealing, compared with SiC-dots in a (100) crystal-Si (c-Si) on insulator substrate. Even in the poor crystal quality substrates of the C+-ion implanted in a-Si and poly-Si layers, we experimentally verified 3C-SiC dot formation by transmission electron microscopy, and the strong photoluminescence (PL) intensity in the near-UV-vis regions, because a-Si is partially poly-crystallized by the high-temperature processes of hot-C+-ion implantation and post-N2 annealing. The PL spectral line shape strongly depends on the Si crystal structures, but the peak PL intensity after N2 annealing is almost independent of the Si crystal structures. Moreover, the PL spectrum can be explained by the sum of PL emissions from different cubic and hexagonal polytypes of SiC. We clarified that the three Si crystal structures have a different contribution ratio of PL components of SiC polytypes.