3C-SiC Crystals Research Articles

Growth and characterization of SiC layers obtained by microwave-CVD

Silicon carbide is a wide band gap semiconductor of interest for its application in many electronic devices. In recent years, a large research activity has been devoted to growth techniques for amorphous, polycrystalline or even epitaxial structures. In this paper, we have reported results on microcrystalline and polycrystalline SiC layers grown by high temperature ECR-CVD over 4″ (100) silicon wafer in SiH4+CH4 gas mixtures. The structure of the films has been investigated by X-ray diffractometry, micro-Raman spectroscopy and transmission electron microscopy (TEM). Stoichiometric SiC films containing a complete chemical order, 3C–SiC crystals with orientation close to that of Si substrate and lateral dimensions larger than 100 nm have been obtained.

Lattice Parameter Measurements of 3C-SiC Thin Films Grown on 6H-SiC(0001) Substrate Crystals

The lattice parameters of 3C-SiC thin films epitaxially grown on 6H-SiC(0001) substrate crystals have been precisely determined by using high resolution x-ray diffraction methods. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections revealed a pseudomorphic growth of the thin film in relation to the substrate lattice, whereas perpendicular to the surface the interplanar spacing of the lattice planes differ slightly ∆d/d = 8.7⋅10. This implicates inherent thin film strain (e) and stress (σ ) components. The in-plane components are found to be ei = 4.8⋅10 and σi = 2.26⋅10 N/m, whereas perpendicular to the surface the thin film strain component is found to be e^ = 2.8⋅10. Introduction Silicon Carbide (SiC) occurs in many polytypes which differ in their periodic stacking sequences of hexagonal and cubic Si-C bilayers. The SiC lattice parameters differ slightly from polytype to polytype [1]. Using x-ray diffraction methods the lattice parameters of 4Hand 6H-SiC single crystal wafers [2] have been determined precisely (Table 1). Unfortunately, large 3C-SiC single crystals are not available. However, 3C-SiC thin films can be easily grown and used to derive the lattice parameters of compact 3C-SiC crystals if one takes the inherent stress, induced by the thin film growth, into account. The 3C-SiC thin films (thickness ≈ 1.2 μm) were grown by solid-source molecular beam epitaxy on (0001)-oriented on-axis 6H-SiC crystal wafers at deposition temperatures between 780°C to 950°C and with growth rates between 30 nm/h to 120 nm/h [3]. High resolution x-ray diffraction of 3C-SiC thin films Although the lattice parameters of the different SiC polytypes differ only slightly, the x-ray diffraction pattern showed, close to each other but well separated, so-called family reflections of the 3C-SiC thin film and 6H-SiC substrate. Using the well known 6H-SiC bulk crystal values (Table 1) as a reference, we could determine the lattice parameters of the 3C-SiC thin films with a corresponding accuracy of 10 for Da/a and 10 for Dc/c. Reciprocal space maps recorded around symmetrical and asymmetrical x-ray reflections (Fig. 1) revealed a pseudomorphous growth of the 3C-SiC thin films in relation to the substrate lattice (Fig. 2). There is no difference between the lateral interplanar spacing of the lattice planes, but perpendicular to the surface their interplanar spacing differ by ∆d/d = 8.7⋅10. The growth direction of the 3C-SiC thin film was found to be [111] with respect to the surface normal. Silicon Carbide and Related Materials (2001). 319-322 319

Origin of Threefold Periodicity in High-Resolution Transmission Electron Microscopy Images of Thin Film Cubic SiC.

: High-resolution transmission electron microscopy (HRTEM) images of the [1-10] zone of cubic SiC layers grown by molecular beam epitaxy (MBE) often reveal regions of material exhibiting an unusual threefold periodicity. The same contrast was found in earlier works of Jepps and Page, who attributed this contrast in HRTEM images of polycrystalline SiC to the 9R-SiC polytype. In this report we demonstrate by HRTEM image simulations that the model of the 9R polytype and an alternative twinning model can fit qualitatively the experimental HRTEM images. However, by comparing the fast Fourier transform (FFT) patterns of the experiments and the simulations, as well as by using dark-field imaging, we show unambiguously that only the model of overlapping twinned 3C-SiC crystals fully agrees with the experiments.

Electron paramagnetic resonance of deep boron acceptors in 4H-SiC and 3C-SiC crystals

EPR spectra of deep boron in 4H-SiC and 3C-SiC crystals have been observed and studied. Two sites in 4H-SiC produced deep-boron EPR signals, quasi-cubic k and hexagonal h. In both cases the deep-boron center symmetry is close to axial along the c crystal axis, and the g factor anisotropy is about an order of magnitude larger than that for shallow boron centers. In the 3C-SiC crystal, the deep-boron symmetry is also close to axial along one of the four 〈111〉 directions. The model proposed for the deep boron center with acceptor properties is BSi-v C, where BSi is the boron substituting for silicon, and v C is the carbon vacancy, with the BSi-v C direction coinciding in 4HSiC with the hexagonal axis of the crystal for both k and h positions. In the cubic 3C-SiC crystal, there are four equivalent deep boron centers, which represent BSi-v C pairs with the bond directed along one of the four 〈111〉 crystal directions.

The Effect of Hydrogen/ Deuterium Introduction on Photoluminescence of 3C-SiC Crystals

ABSTRACTThe effect of the incorporation and annealing of deuterium in 3C-SiC on its photoluninescence is reported. A 3C-SiC crystal has been implanted with 100 keV deuterium and subsequently annealed at temperatures between 1015 °C and 1220 °C for 1 to 5 minutes. SIMS depth profiles indicate hydrogen is strongly trapped by defects generated through ion bombardment, but a gradual damage repairing occurs during annealing. Photoluminescence was measured with 488 nm Ar laser excitation for sample temperatures from 89 K to 400 K. The PL peak wavelength of 540 nm at room temperature has shifted to 538 nm at 89 K. The peak PL intensity decreases with measurement temperature while its full width at half maximum (FWHM) exhibits an increasing trend. PL data were taken at five annealing stages. The post-implantation peak PL intensity and its integrated area increase initially with annealing temperature and time. After the final annealing at 1218 °C for 2 minute, PL intensity and its integrated area exhibit a decrease in level.

Characterization of 3C–SiC crystals grown by thermal decomposition of methyltrichlorosilane

Single crystal 3C–SiC platelets, formed by thermal decomposition of methyltrichlorosilane at 1650–1750 °C, have been characterized in terms of structure and morphology. The platelets are ∼3–5 mm in length and 1–1.5 mm in thickness. The (111) C face of the crystal, which has an effective zero growth rate, presents a large, mirrorlike surface in the as-grown 3C crystals. Atomic force microscopy indicates that these as-grown surfaces are extraordinarily flat and uniform, with a mean surface roughness of 1–2 Å. This value is comparable with the roughness of state-of-art polished Si wafers. X-ray rocking curves of the 〈111〉 peak were obtained with a linewidth of 12.3 arcsec. This is the smallest value reported to date for any polytype of SiC. Raman spectroscopy at 300 K reveals a very sharp TO–phonon peak at 797.8 cm−1, with a linewidth of 2.1 cm−1.

Are polytype transitions possible during boron diffusion?

The influence of boron diffusion on the polytype structure of 3C, 6H and 15R SiC polytypes was studied in the temperature range 1600–1900 °C. In the surface region partial polytype transitions 15R → 3C and 6H → 3C were detected by reflection high energy electron diffraction. In the bulk region such diffraction spots could not be detected. A maximum of the diffraction intensities of 3C in α-SiC was observed at 1800°C, whereas in the temperature range 1600–1800°C no phase transitions in the 3C SiC crystal were detected. At 1800°C and for long diffusion times a phase transition of the type 3C → 15R occur. This reverse phase transition may be the cause of the decrease in diffraction spot intensities of 3C SiC in 15R and 6H crystals in comparison with crystals treated by boron diffusion at lower temperatures. Reasons for the observed polytype transitions are the local generation of stacking faults which lead to elimination of the hexagonal sites in the stacking order of the α-SiC polytypes and their stabilization by the diffusion distribution induced stress field.

Electronic band structure and optical properties of cubic silicon carbide crystals

The electroreflectance spectra of cubic silicon carbide crystals are measured in the range 1.0 to 5.6 eV. The energies of direct optical transitions are determined using a multiple oscillator model. The electronic band structure and optical functions of 3C-SiC crystals are calculated by semiempirical pseudopotential methods. From comparison between theoretical and experimental optical spectra numerical parameters of electronic band structure 3C-SiC are obtained, and values of atomic form factors of carbon atoms, giving the realistic band structure and optical spectra of 3C-SiC, are determined.

Low-temperature growth and its growth mechanisms of 3C-SiC crystal by gas source molecular beam epitaxial method

Low-temperature growth of epitaxial 3C-SiC films on the just cut and 4° off-Si(111) substrates were performed by gas source molecular beam epitaxial method. Also the irradiation effect of ArF laser was briefly examined. Two kinds of gaseous combinations such as SiHCl 3-C 2H 4 and SiHCl 3-C 3H 8 systems were used to achieve the stoichiometric growth at low temperature. These gases were first thermally cracked at 1000°C and deposited on the substrates. From detailed examinations of the reaction mechanism for this growt method, we concluded that the growth was performed under the conditions of a three-temperature method of MBE in both gaseous systems. Using these cracked species, 3C-SiC films having good crystallinity could be grown at 1000 and 800°C in the SiHCl 3-C 2H 4 and SiHCl 3-C 3H 8 systems, respectively. Currently, it seems that the growth temperature of 800°C is the lowest as compared with other works. We consider that such a low-temperature growth can be performed by the reactions of cracked species at the hollow bridge sites which exist on (111) terraced surface. The ArF laser irradiation was found to enhance the SiC crystallization reaction.

Electron spin resonance in electron-irradiated 3C-SiC

Electron-irradiation-induced defects in epitaxially grown 3C-SiC crystals have been studied by electron-spin-resonance (ESR) measurements. The results indicate the presence of an isotropic ESR center that consists of five lines equally spaced at about 1.5 G and has a g value of 2.0029±0.0001. Isochronal and isothermal annealing of electron-irradiated 3C-SiC showed that this center was annealed at three stages (150, 350, and 750 °C) and that the 750 °C stage exhibited first-order reaction with an activation energy of 2.2±0.3 eV.

High-Pressure Studies of Absorption and Luminescence Spectra in 3C–SiC

The pressure dependence of absorption spectra in 3C-SiC crystals has been studied up to 14 GPa at room temperature by using a diamond anvil cell. The pressure derivative of the fundamental gap between \(\varGamma_{\text{v}}\) and X c band extrema is found to be -1.9 meV/GPa, the absolute value of which is anomalously small, in contrast with the values usually observed for \(\varGamma_{\text{v}}{-}X_{\text{c}}\) (or Δ c ) gaps in the diamond and zinc-blende structure semiconductors or insulators. Luminscence spectra measured at 1.8 K reveal that the binding energy of excitons trapped by donors increases drastically at pressures higher than 4 GPa.