3C-SiC Crystals Research Articles

Growth of cubic SiC single crystals by the physical vapor transport technique

Suitable process parameters for the growth of cubic 3C-SiC single crystals via the seeded physical vapor transport (PVT) technique, also known as the modified Lely method, have been determined. Free-standing, 200 μm thick 3C-SiC epilayers with (0 0 1)- or (0 0 1¯)-face grown on undulant Si (0 0 1) as well as 3C-SiC platelets with [1 1 1]- or [1¯ 1¯ 1¯]-orientation grown by thermal decomposition of methyl trichlorosilane in hydrogen were employed as seed crystals. The source material consisted of stoichiometric SiC; in addition, a separate Si source was deposited in the furnace at a temperature of about 1500 °C. The temperature of the seed crystals was kept at about 1900 °C. Stable growth of 3C-SiC bulk material of high crystalline quality was reached on 3C-SiC seed crystals with (0 0 1)-face providing a low density of planar defects and at near-thermal-equilibrium conditions resulting in a reduction of internal stress and as a consequence in avoiding the generation of new extended crystal defects. The growth rate achieved under these conditions was approximately 0.05 mm/h. The nitrogen donor concentration in the grown 3C-SiC crystals was determined to be equal to (2–6)×10 18 cm −3.

Synthesis of silicon carbide nanorods without defects by direct heating method

High quality silicon carbide single crystal nanorods were successfully synthesized through gas–solid reaction between silicon and multiwall carbon nanotubes (CNTS) by direct heating methods. The X-ray diffraction (XRD) analysis showed that the reaction product of Si vapor with CNTS is β-SiC. SEM and HRTEM images suggested that the SiC nanorods are 3C-SiC single crystals almost free of defects. Based on these results, it is presumed that the reaction first took place at an end of CNTS giving β-SiC nuclei, one of which with its [111] parallel to the tube direction could grow consecutively along this direction so that a straight and solid SiC single crystal rod was formed without defects.

High-Temperature Nucleation of Cubic Silicon Carbide on (0001) Hexagonal-SiC Nominal Surfaces

The development of 3C-SiC crystals from oriented hexagonal seed has always suffered from systematic twinning that appears during the nucleation step of the layer. To investigate the possibility to reduce or eliminate the incoherent twin boundaries at high temperature (for conditions close to bulk growth ones), we conducted an experimental study on 3C-SiC nucleation. A mechanism for the selection of one 3C-SiC orientation among the two possible is proposed. It is based on a strong interaction between the α-SiC substrate steps and the anisotropic lateral expansion of the β-SiC domains. This model is confirmed by cross-sectional high resolution transmission microscopy observations of the α−β interface. The mechanism is discussed with respect to the surface polarity (Si or C faces), the miscut angle, and the substrate polytype.

Raman Scattering Analyses of Stacking Faults in 3C-SiC Crystals

Visible and deep UV Raman measurements have been applied to investigate the structural and electrical properties of stacking disordered 3C-SiC crystals. It is found that free-carrier density shows the significant dependence on the density of stacking faults in 3C-SiC. The density of stacking faults has been estimated from the comparison between experimentally obtained Raman spectra and Raman intensity profiles simulated using one-dimensional lattice models considering the disorder in bond polarizability arrangement.

Improvement of cubic silicon carbide crystals grown from solution

Abstract Cubic-silicon carbide crystals have been grown from carbon-rich silicon solutions using the travelling-zone method. To improve the growth process, we investigated the effect of controlling more tightly some of the growth parameters. Using such improved growth conditions, our best sample is a 12 mm diameter and ∼3 mm long 3C–SiC crystal. It is grown on a (0001) 2∘ off, 6H–SiC seed and has 〈 111 〉 -orientation. The low amount of silicon inclusions results in a reduced internal stress, which is demonstrated by the consideration of μ -Raman spectra collected at room temperature on a large number of samples.

Oscillatory structure in radiation spectra of individual microplasmas in silicon carbide p-n-junctions

The breakdown electroluminescence spectra of individual microplasmas in a p-n-junction with microplasma breakdown, which was prepared on a 3C-SiC crystal, have been investigated. The clear periodic structure of an oscillatory nature, which was discovered first by the authors recently, with a period of about 0.16 eV was observed in the emission spectra of this microplasma. The oscillations were superimposed over the entire investigated spectral region between 1.8–4.7 eV. The amplitude of the oscillations amounted to 0.05–0.25 of the background radiation intensity. The characteristics of the oscillatory structure and of the background radiation have been separated and compared. It turned out that they depend in different ways on the temperature and on the sample-powering regime. It has been revealed that the oscillatory structure is associated apparently with the energy transition (X3c−X1c) in the conduction band.

Characteristics of SiC Heteroepitaxial Growth on Si by Hot-Mesh Chemical Vapor Deposition

The heteroepitaxial growth of 3C-SiC films on Si(100) substrates by the hot-mesh chemical vapor deposition (HM-CVD) method using monomethylsilane as a source gas was investigated. From the results of X-ray diffraction spectra, 3C-SiC crystal was epitaxially grown on Si substrates at substrate temperatures above 750°C. The SiC/Si interface was observed by cross-sectional scanning electron microscopy, and was confirmed to be void-free and smooth. The density of hydrogen radicals supplied to the substrate surface during the growth was also estimated measuring the optical absorbance change of tungsten phosphate glass plates. From the dependence of the growth rate on substrate temperature, the mechanism of SiC film growth by HM-CVD was considered.

Pressure Effect on the Elastic Properties of SiC Polytypes

The pressure dependences of the second-order elastic constants ij C and the velocity of sound in 3C-SiC and 2H-SiC crystals are calculated in the framework of the Keating model with the additional assumption that the central α and the noncentral β force constants are linear functions of external hydrostatic pressure. Grüneisen parameters for the different acoustic modes of 3C-SiC have been also calculated. The third –order elastic constants ijk C for 3C-SiC are determined from the dependences of ij C on the pressure.

Suppression Mechanism of Double Positioning Growth in 3C-SiC(111) Crystal by Using an Off-Axis Si(110) Substrate

Hetero-epitaxial CVD growth of 3C-SiC on a Si(110) substrate gives a (111) crystal with low defects density. However, double positioning growth often disturbs growth of a single crystal. The growth on an off-axis Si(110) substrate suppressed propagation of the double positioning defects in the grown layer effectively. Cross-sectional transmission electron microscopy revealed the details of the suppression process on the off-axis substrate. The suppression mechanism and the origin of the defects formation at double positioning boundaries were interpreted by the growth model based on an anisotropic growth rate on (111) plane of 3C-SiC.

Suppression of the Twin Formation in CVD Growth of (111) 3C-SiC on (110) Si Substrate

Chemical vapor deposition of (111) 3C-SiC on (110) Si substrate was carried out, and the effect of the substrate off-axis introduced on (110) Si substrate for suppressing the twin formation in 3C-SiC hetero-epitaxial layers was investigated. From the growth on hemispherically polished (110) Si substrate, it was found that the off-axis toward the [001] Si axis had a noble effect for suppressing the twin formation, while the off-axis toward the [110] Si axis was ineffective. The growth of single 3C-SiC crystal containing few double positioning boundaries, which are related with the twin formation, was demonstrated on the (110) Si substrate 3° off-axis toward the [001] Si axis. Transmission electron microscopic observation revealed that double positioning boundaries on the (110) Si substrate off-axis toward the [001] Si axis were nearly eliminated within the initial a few hundreds nano meter in thickness.

Influence of Substrate Roughness on the Formation of Defects in 3C-SiC Grown on Si(110) Substrate by Hetero-Epitaxial CVD Method

Interfaces between a Si(110) substrate and 3C-SiC crystals grown hetero-epitaxially by CVD were investigated by cross-sectional transmission electron microscopy. Gas flow condition during the carbonization process affects the roughness of the substrate surface and there is an optimum condition to preserve the flat surface. High quality 3C-SiC crystals grew only on the flat substrate, with crystallographic relationship of Si[1-10]//SiC[1-10] and Si[001]//SiC[1-1 - 2], because the well-lattice-match relationship was limited in a two-dimensional region at the SiC(111)/Si(110) interface. Using the optimum condition, some kinds of roughness at an atomic scale remained on the surface of the substrate. Nanoscopic observation of the crystals grown on an off-axis substrate revealed the influence of the roughness on the epitaxial growth and the defects generation at the interface.

Low-Temperature Heteroepitaxial Growth of SiC on (100) Si Using Hot-Mesh Chemical Vapor Deposition

The crystal growth of 3C-SiC films on (100) Si substrates by the hot-mesh chemical vapor deposition (HMCVD) method using monomethylsilane (MMS) as a source gas was investigated. A mesh structure of hot tungsten (W) wire was used as a catalyzer. At substrate temperatures above 750°C and at a mesh temperature of 1600°C, 3C-SiC crystal was epitaxially grown on Si substrates. From the X-ray rocking curve spectra of the (311) peak, SiC was also epitaxially grown in the substrate plane. From the dependence of growth rate on substrate temperature and W-mesh temperature, the growth mechanism of SiC films by HMCVD was considered.

Hot-mesh Chemical Vapor Deposition for 3C-SiC Growth on Si and SiO2

AbstractThe crystal growth of SiC films on (100) Si and thermally oxidized Si (SiO2/Si) substrates by hot-mesh chemical vapor deposition (HMCVD) using monomethylsilane as a source gas was investigated. A mesh structure of hot tungsten (W) wire was used as a catalyzer. At substrate temperatures above 750°C and at a mesh temperature of 1600°C, 3C-SiC crystal was epitaxially grown on (100) Si substrates. From the X-ray rocking curve spectra of the (311) peak, SiC was also epitaxially grown in the substrate plane. On the basis of the X-ray diffraction (XRD) measurements, on the other hand, the growth of (100)-oriented 3C-SiC films on SiO2/Si substrates was determined to be achieved at substrate temperatures of 750-800°C, while polycrystalline SiC films, at substrate temperatures above 850°C. From the dependence of growth rate on substrate temperature and W-mesh temperature, the growth mechanism of SiC crystal by HMCVD was discussed.

Lateral epitaxial overgrowth and reduction in defect density of 3C-SiC on patterned Si substrates

Selective growth and reduction of defects of cubic silicon carbide (3C-SiC) crystals grown within windows and laterally over SiO2 masks patterned on Si substrates are presented. The growth has been performed via chemical vapor deposition using hexachlorodisilane and propane, as well as hexamethyldisilane. Lateral epitaxial overgrowth (LEO) was achieved at selected areas where windows are square or array of stripes. The LEO process was characterized mainly by atomic force microscopy.3C-SiC grew epitaxially on Si inside the window of SiO2 mask, and after filling up the window area, SiC grew laterally onto the SiO2 mask. The LEO begins with appearance and growth of (112) facets of 3C-SiC, and finally, the fronts of laterally overgrown SiC from the opposite sides of windows coalesce with each other. If the mask is an array of rectangular stripes, the coalescence point becomes a seam. Cathodoluminescence micrographs showed the absence of dislocations in the LEO region and the presence at the seam lines. Although many rectangular-shaped pits are observed in the area of epitaxially grown 3C-SiC, they disappeared in the LEO regions. This suggests the pits being originated upon epitaxy of 3C-SiC on Si and expanded to form rectangular shape on the final surface.

Effect of pressure on the elastic properties of silicon carbide

The pressure dependences of the second-order elastic constants Cij and the velocity of sound in 3C-SiC and 2H-SiC crystals are calculated in the framework of the Keating model. The third-order elastic constants Cijk for 3C-SiC are determined from the dependences of the second-order elastic constants Cij on the pressure p.

Si c(4×4) structure appeared in the initial stage of 3C-SiC epitaxial growth on Si(0 0 1) using monomethylsilane and dimethylsilane

The Si c(4×4) structure formed on Si(001)-(2×1) surface using monomethylsilane (MMS) and dimethylsilane (DMS) was studied by reflection high-energy electron diffraction (RHEED), X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). From the XPS measurement, it was found that SiC bonds existed in the Si c(4×4) surface layer. The crystal structure of surface layer, however, was not the one of cubic SiC (3C-SiC) crystal, because 3C-SiC spots were not observed on RHEED pattern. Therefore, Si1−xCx alloy layer would have been formed on the surface. From the angle-resolved XPS (AR-XPS) measurement, the thickness of the alloy layer was estimated to be 0.3nm. From the AFM images of the Si surface after SiC nucleation, the Si c(4×4) layer is considered to play a role as buffer layer relaxing the lattice mismatch between Si and SiC.

Synthesis and growth of 3C-SiC crystals from solution at 950°C

In order to reduce the growth temperature of SiC crystals, Ga–Al–Si and/or Sn–Al–Si solution, in which the Si content was just below the saturation value, was reacted with C 3H 8 gas at 950°C. After a 10 h-reaction, many small crystals were found in the solution. X-ray diffraction measurements revealed that the crystals are 3C-SiC. Using the wetting solution of these solutions, 3C-SiC crystal layers could be grown on a 6H-SiC substrate.

Orientation dependence of solid phase growth of implantation-induced amorphous layer in 6H–SiC

The orientation dependence of solid phase growth of the implantation-induced amorphous layer on (0 0 0 1)- and (1 1 ̄ 0 0) -oriented 6H–SiC has been investigated at annealing temperatures below 1000°C using transmission electron microscopy. The surface region of the sample is amorphized by the 100 keV-Ar + implantation at a dose rate of 2×10 15 cm −2. The amorphous layer in the (1 1 ̄ 0 0) -oriented 6H–SiC is epitaxially regrown with a uniform regrowth rate (4.4 nm/min at 770°C). For the (0 0 0 1)-oriented 6H–SiC, the annealing of the amorphous layer leads to the regrowth of the micro-twinned 3C–SiC crystals with a regrowth rate of 0.019 nm/min at 770°C and an activation energy of 3.4 eV, followed by a faster regrowth of highly oriented 3C–SiC crystals. A change of the regrowth mechanism in the regrowth of the implantation-induced amorphous layer to 3C–SiC is suggested.

Optical and structural properties of SiC layers grown by an electron cyclotron resonance CVD technique

Large area microcrystalline and polycrystalline SiC thin films have been grown by electron cyclotron resonance CVD over (100) silicon wafers. The samples have been characterized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), micro-Raman and photo luminescence spectroscopy. Stoichiometric SiC films containing 3C–SiC crystals with orientation close to that of Si substrate and lateral grain dimension up to 1400 Å were obtained under suitable deposition conditions. They also exhibit blue photoluminescence at room temperature in the range of 400–450 nm with features dependent on their structure.

Liquid phase epitaxial growth of 3C-SiC films deposited on Si

In this paper, we present a novel method to grow 3C-SiC crystal in a liquid-phase epitaxy-like manner, but without any substantial substrate. The starting material to be used in this method is the 3C-SiC-thin film deposited on Si substrate in a gas-phase heteroepitaxial technology. The free 3C-SiC film which remained of the molten Si substrate epitaxially grows up from the Si solution saturated by SiC in a highly purified graphite crucible heated by an inductive heater. XRD, XPS and Raman spectroscopy were used to characterize the samples. The only one peak with full width at half maximum (FWHM) of 0.2 at 2θ=35.65° in XRD is attributed to the diffraction of (111) planes in 3C-SiC. The energy difference between C1s and Si2p binding energy in XPS data is 183.2 eV, which is well consistent with the result published before for single crystal 3C-SiC. Although the only sharp and strongest peak at 796.6 cm −1 in the Raman spectrum also confirms the crystal structure, the additional broadened weak peak at 523.6 cm −1 may imply the existence of some lattice defects related to nitrogen unintentionally introduced in the growth process.