Hexagonal 6H-SiC Research Articles

CVD diamond-SiC composite films: Structure and electrical properties

Thin films of microcrystalline diamond-silicon carbide composite have been deposited by microwave plasma chemical vapor deposition (CVD) in methane-silane-hydrogen gas mixtures on Si substrates with an insulating polycrystalline diamond buffer layer. The structure and phase composition of the films were characterized by scanning electron microscopy, Raman and photoluminescence spectroscopy. The silicon carbide grains are identified to be cubic polytype 3C-SiC with only a minor admixture of hexagonal 6H-SiC. The measured electrical resistivity of the films is found to decrease with the temperature from ~10−1 Ω·cm at 300 K to ~10−2 Ω·cm at 460 K, with activation energy Ea = 0.20 eV. The conductivity is assumed to be realized via pathways in the SiC network immersed in isolating diamond matrix. The obtained results show that such diamond/SiC composites may be considered as an alternative to electrically conductive nitrogenated ultrananocrystalline diamond films for a number of practical applications.

Polycarbosilane facilitated growth of SiC nanowires from biowaste coconut shell

ABSTRACT The SiC nanowires were synthesised by the pyrolysis of a mixture of agricultural waste coconut shell (CS) and polycarbosilane (PCS) precursor at 1400°C. The characterisation of synthesised nanowires was carried out by X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The single crystalline cubic β-SiC nanowires were found to be grown on <111> directions along (111) planes. The SiC nanowires had striped morphology containing stacking faults and twins as a planar defect. The extensive growth of SiC nanowires was owing to the continuous deposition of SiO and CO gaseous over the tiny SiC nuclei from the amorphous SiOC matrix. The vapour–solid (VS) and vapour–phase (VP) mechanisms have played the dominant role in nanowire formation. The 3C-SiC nanowires had striped morphology containing hexagonal 4H-SiC and 6H-SiC stacking faults.

Создание темплейтов для гомоэпитаксиального роста 3C-SiC методом прямого сращивания пластин карбида кремния различающихся политипов

An approach of direct bonding of SiC wafers of differing polytypes has been implemented in order to create a template for cubic 3C-SiC homoepitaxy. Heteroepitaxial 3C-SiC layers grown by chemical vapor deposition were transferred onto a hexagonal 6H-SiC wafer. The results of structural characterization showed that the quality of 3C-SiC sublimation epitaxy on the templates is comparable to the level of epitaxy of cubic silicon carbide by chemical vapor deposition method. It was confirmed that the 3С-SiC layer transferred onto the 6H-SiC substrate plays the role of a crystalline "seed" that determines cubic polytype of the overgrown SiC layer.

Templates for homoepitaxial growth of 3C-SiC obtained by direct bonding of silicon carbide wafers of differing polytype

An approach of direct bonding of SiC wafers of differing polytypes has been implemented in order to create a template for cubic 3C-SiC homoepitaxy. Heteroepitaxial 3C-SiC layers grown by chemical vapor deposition were transferred onto a hexagonal 6H-SiC wafer. The results of structural characterization showed that the quality of 3C-SiC sublimation epitaxy on the templates is comparable to the level of epitaxy of cubic silicon carbide by chemical vapor deposition method. It was confirmed that the 3C-SiC layer transferred onto the 6H-SiC substrate plays the role of a crystalline &amp;quot;seed&amp;quot; that determines cubic polytype of the overgrown SiC layer. Keywords: Silicon carbide, polytypes, direct bonding, templates, sublimation epitaxy.

3C-SiC growth by sublimation in vacuum technology optimization

Results of an epitaxial growth of 3C-SiC epilayers on hexagonal 6H-SiC, 4H-SiC substrates are described. The study of the obtained epitaxial layers grown on 6H substrates was made by photoluminescence and optical microscopy. Also, an image analysis of the interface of 3C-SiC epitaxial layers with 6H, 4H, and 15R substrates obtained by Transmission Electron Microscopy (TEM) are presented. Difference between the layers on the Si and C faces are discussed.

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.

Enhanced Phase Transition Properties of VO2 Thin Films on 6H-SiC (0001) Substrate Prepared by Pulsed Laser Deposition.

For growing high quality epitaxial VO2 thin films, the substrate with suitable lattice parameters is very important if considering the lattice matching. In addition, the thermal conductivity between the substrate and epitaxial film should be also considered. Interestingly, the c-plane of hexagonal 6H-SiC with high thermal conductivity has a similar lattice structure to the VO2 (010), which enables epitaxial growth of high quality VO2 films on 6H-SiC substrates. In the current study, we deposited VO2 thin films directly on 6H-SiC (0001) single-crystal substrates by pulsed laser deposition (PLD) and systematically investigated the crystal structures and surface morphologies of the films as the function of growth temperature and film thickness. With optimized conditions, the obtained epitaxial VO2 film showed pure monoclinic phase structure and excellent phase transition properties. Across the phase transition from monoclinic structure (M1) to tetragonal rutile structure (R), the VO2/6H-SiC (0001) film demonstrated a sharp resistance change up to five orders of magnitude and a narrow hysteresis width of only 3.3 °C.

Lattice sites of ion-implanted Mn, Fe and Ni in 6H-SiC

Using radioactive isotopes produced at the CERN-ISOLDE facility, the lattice location of the implanted transition metal (TM) ions 56Mn, 59Fe and 65Ni in n-type single-crystalline hexagonal 6H-SiC was studied by means of the emission channeling technique. TM probes on carbon coordinated tetrahedral interstitial sites (TC) and on substitutional silicon sites (SSi,h+k) were identified. We tested for but found no indication that the TM distribution on SSi sites deviates from the statistical mixture of 1/3 hexagonal and 2/3 cubic sites present in the 6H crystal. The TM atoms partially disappear from TC positions during annealing at temperatures between 500 °C and 700 °C which is accompanied by an increase on SSi and random sites. From the temperature associated with these site changes, interstitial migration energies of 1.7–2.7 eV for Mn and Ni, and 2.3–3.2 eV for Fe were estimated. TM lattice locations are compared to previous results obtained in 3C-SiC using the same technique.

RHEED intensities from two-dimensional heteroepitaxial nanoscale systems of GaN on a 3C-SiC(111) surface

This paper presents a version of simulation program, which facilitates the calculation of changes to the intensity of RHEED oscillations in the function of the glancing angle of incidence of the electron beam, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC surface, including the possible existence of various diffuse scattering models through the layer parallel to the surface. New version program summaryTitle of program: RHEED_DIFF_ZProgram Files doi:http://dx.doi.org/10.17632/52nxmwzkxx.1Licensing provisions: GNU General Public License 3Programming language used: C++Journal reference of previous version: Computer Physics Communications 207 (2016) 536–538Does the new version supersede the previous version?: No. It is a supplement to the previous version.Reasons for new version:Responding to users’ feedback we present a practical procedure of construction of simulation program, which facilitates the calculation of changes to the intensity of RHEED rocking curves, employing various models of scattering crystal potential for heteroepitaxial structure of hexagonal (0001) GaN film nucleated on a 3C-SiC(111) surface.Nature of problem:Growth of GaN layers on SiC is of importance for potential electronic device applications.Silicon carbide crystallizes in numerous different modifications, so-called polytypes [1]. Among them, only hexagonal structure 4H-SiC and 6H-SiC have been thoroughly investigated while the cubic 3C-SiC polytype is lagging behind in technological developments. The 3C-SiC has a Zincblende crystal structure and is characterized by an identical orientation of all bilayers in the crystal, where the atomic geometry is repeated every three bilayers along the c-axis this crystal structure (Fig. 1). For this reason, 3C-SiC has the high electron mobility and saturation velocity by reducing phonon scattering resulting from the high symmetry. The lattice mismatch between GaN(0001) and 3C-SiC(111) is about 3.3%, and is smaller than the mismatch between GaN(0001) and Si(111) [2]. Therefore progress in investigations on crystal growth of GaN on 3C-SiC is a key issue for device developments related to this heterostructure. Researchers and technologists manufacturing two-dimensional heterostructures frequently use RHEED rocking curves to control growth of samples at the atomistic level of accuracy. The fundamental scientific problem in such research is to specify both interface type and growth mechanism for subsequent layers.Method of solution:RHEED intensities are calculated within the general framework described in Refs. [2] and [3].Summary of revisions:The presented version of the program implements an original algorithm of self-consistent calculations for scattering potentials GaN(0001)/3C-SiC(111) and solving a time-independent Schrödinger equation for high-energy electrons.During the numerical calculations of the changes in the intensity of the specular beam in the function of the glancing angle, it was assumed that the azimuth of the incident beam direction corresponds to the one-beam condition, the electron energy equals 10 keV, the glancing angle was increased from 0.5∘ to 6.5∘, and the value of αparameter=0.1 and β=0.5 for the MODEL3 of the scattering potential [3] with the model of ideal SiC/GaN interface [4].

Moissanite (SiC) with metal-silicide and silicon inclusions from tuff of Israel: Raman spectroscopy and electron microscope studies

Here, we present studies of natural SiC that occurs in situ in tuff related to the Miocene alkaline basalt formation deposited in northern part of Israel. Raman spectroscopy, SEM and FIB-assisted TEM studies revealed that SiC is primarily hexagonal polytypes 4H-SiC and 6H-SiC, and that the 4H-SiC polytype is the predominant phase. Both SiC polytypes contain crystalline inclusions of silicon (Sio) and inclusions of metal-silicide with varying compositions (e.g. Si58V25Ti12Cr3Fe2, Si41Fe24Ti20Ni7V5Zr3, and Si43Fe40Ni17). The silicides crystal structure parameters match Si2TiV5 (Pm-3m space group, cubic), FeSi2Ti (Pbam space group, orthorhombic), and FeSi2 (Cmca space group, orthorhombic) respectively. We hypothesize that SiC was formed in a local ultra-reduced environment at respectively shallow depths (60–100 km), through a reaction of SiO2 with highly reducing fluids (H2O–CH4–H2–C2H6) arisen from the mantle “hot spot” and passing through alkaline basalt magma reservoir. SiO2 interacting with the fluids may originate from the walls of the crustal rocks surrounding this magmatic reservoir. This process led to the formation of SiC and accompanied by the reducing of metal-oxides to native metals, alloys, and silicides. The latter were trapped by SiC during its growth. Hence, interplate “hot spot” alkali basalt volcanism can now be included as a geological environment where SiC, silicon, and silicides can be found.

Monte Carlo Study of the early Growth Stages of 3C-SiC on Misoriented &amp;lt;11-20&amp;gt; and &amp;lt;1-100&amp;gt; 6H-SiC Substrates: Role of Step-Island Interaction

In this paper 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 hexagonal 6H-SiC step-bunched substrates with miscuts towards the &lt;11-20&gt; and &lt;1-100&gt; directions. We find that the preferential 3C conversion observed on &lt;1-100&gt; misoriented substrates could be due to a different step-to-island interaction which enhances island stability and expansion in this specific direction. For this reason 3-4° degrees off step-bunched 6H substrates with miscut towards the &lt;1-100&gt; direction should be the best choice for the stable and reproducible hetero-polytypical growth of high quality cubic epitaxial films.

Adsorbed O2 on the Graphite‐Induced Growth of Ultra‐Long Single‐Crystalline 6H–SiC Nanowires

Large‐scale ultra‐long 6H–SiC nanowires were in situ synthesized on the as‐prepared SiC–Si ceramic substrate using graphite as the carbon source and substrate as the silicon source via improving the adsorbed O2 content on the graphite precursors using milling technology. The as‐grown nanowires were typical single crystal of hexagonal 6H–SiC with diameters of 50–100 nm and lengths of up to several millimeters (or even centimeters). Vapor‐solid mechanism was proposed for the growth mode of the as‐grown ultra‐long 6H–SiC nanowires. This study not only provided new insight into the growth mode for in situ synthesizing 6H–SiC nanowires on silicon‐based ceramics, but also suggested a new design methodology for synthesizing ultra‐long nanowires.

Monte Carlo Study of the Early Growth Stages of 3C-SiC on Misoriented and 6H-Sic Substrates

In this paper we used three dimensional kinetic Monte Carlo simulations on super-lattices to study the hetero-polytypical growth of cubic silicon carbide polytype (3C-SiC) on hexagonal 6H-SiC substrates with miscuts towards the &lt;11-20&gt; and &lt;1-100&gt; directions. We analyze the grown film for different miscut angles (in the range 2° to 12° degrees) and different growth rates, finding that substrates with miscut of 3-4° degrees towards the &lt;1-100&gt; direction should be the best choice for the growth of high quality cubic epitaxial films, being able to promote, given a suitable pre-growth treatment to induce step bunching, the nucleation of single domain 3C-SiC films.

Thermal Conductivity of Hexagonal SiC Nanowire by Nonequilibrium Molecular Dynamics Simulations

Using nonequilibrium Molecular Dynamics method, thermal properties of hexagonal 4H-SiC and 6H-SiC nanowires are investigated. The quantum errors between realistic temperatures and Molecular dynamics temperatures are rectified based on Density Functional Theory. Thermal conductivities of 4H-SiC and 6H-SiC nanowires are both simulated from 50K to 800K. The scale effect on the thermal conductivity of nanowire is also investigated by varying the nanowires length from 10nm to 130nm. Results indicate, if the length of phonon mean free path is shorter than that of nanowire, phonon-surface scattering will surpass boundary scattering to contribute thermal resistances. Therefore, the thermal conductivity of 4H-SiC or 6H-SiC nanowire is mainly determined by the comparability between the length of nanowires and phonon mean free path.

First-principles molecular dynamics study on temperature-dependent dielectric function of bulk 3C and 6H SiC in the energy range 3–8 eV

The present work aims at investigating the temperature-dependent dielectric function of cubic (3C) and hexagonal (6H) SiC in the energy range 3–8eV. To compute the temperature effect, the first-principles molecular dynamics (FPMD) method is implemented that can effectively calculate the finite temperature electronic band structure, density of states and dielectric function. In comparison with experimental data, the FPMD approach successfully predicts the dielectric spectra of 3C and 6H SiC over the temperature range from 90K to 538K. The convincing results enable us to predict the dielectric function of SiC at higher temperature.

Heteroepitaxial Growth of 3C-SiC on Polar Faces of 6H-SiC Substrates, TEM Investigations

Abstract Results of an epitaxial growth of 3C-SiC epilayers on Si (0001) and C(000¯1) faces of hexagonal 6H-SiC substrates are described. TEM study of grown layers as well as interface between cubic and hexagonal polytypes is presented. Difference between the layers on the Si and C faces are discussed.

Palladium assisted silver transport in polycrystalline SiC

The transport of silver in polycrystalline 3C-SiC and hexagonal 6H-SiC has been investigated by annealing the SiC samples in contact with a Pd–Ag compound at temperatures of 800 and 1000°C and times of 24 and 67h. The Pd was added in an attempt to improve the low wetting of SiC by Ag and further because Pd is produced in measurable concentrations in coated particles during reactor operation. Pd is also known to coalesce at the IPyC–SiC interface and to chemically attack the SiC layer. SEM, TEM and EDS were used to show that the Ag penetrates polycrystalline SiC along grain boundaries together with Pd. It is suggested that Ag transport in SiC takes place along grain boundaries in the form of moving nodules consisting of a Ag–Pd mixture. It is assumed that the nodules move along grain boundaries by dissolving the SiC at the leading edge followed by the reprecipitation of SiC at the trailing edge. Since the solubility of Cs in Ag and Pd is extremely low, it is unlikely that Cs will penetrate the SiC together with the Ag–Pd compound if present at the IPyC–SiC interface. If it is assumed that the dominant transport mechanism of Ag in intact polycrystalline SiC is indeed the Pd assisted mechanism, then the stabilization of Pd (and other metallic fission products) in the kernel could be a way of mitigating Ag release from TRISO-coated particles.

Interface structure of graphene on SiC: an ab initio and STM approach

High temperature treatment of SiC surfaces is a well-established technique for producing graphene directly on top of an insulating substrate. In this domain an important question is the influence of the substrate on the atomic and electronic structure of the graphene layers. This requires a detailed investigation of the interactions at the graphene–SiC interface. Surface science techniques and ab initio calculations are well suited for that purpose. In this paper, we present a brief review of the recent investigations performed in this domain by scanning tunnelling microscopy (STM) and ab initio simulations. It is largely based on the work performed in our group, but it also provides a survey of the literature in these fields. Both the so-called Si and C face of the hexagonal 6H(4H)SiC{0 0 0 1} substrates will be considered, as they show markedly different types of behaviour.

Studying edge luminescence of n-3C-SiC epilayers grown on 6H-SiC substrates

Epitaxial films of cubic silicon carbide (n-3C-SiC) polytype grown on hexagonal (6H-SiC) polytype substrates by sublimation epitaxy in vacuum have been studied. The films of the best structural quality exhibit low-temperature photoluminescence related to the recombination of bound excitons. The results are compared to the available data for volume 3C-SiC crystals.

Preparation of silicon carbide using bamboo charcoal as carbon source

Silicon carbide (SiC) was prepared by carbothermal reduction with amorphous silica sol as silicon source and bamboo charcoal powder as carbon source. The compositions and microstructure of prepared SiC were investigated by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). XRD of prepared SiC showed that the major phase of prepared SiC was hexagonal 6H-SiC with the existence of some 4H-SiC. SEM showed that SiC particle was granular, rod-like and of tower-shape, and it inherited the shape of bamboo charcoal. EDS showed that prepared SiC was pure without being doped by the mineral elements from bamboo charcoal.