Woo Sik Yoo

Growth mechanism of 6H-SiC in step-controlled epitaxy

Growth of SiC on off‐oriented 6H‐SiC{0001} substrates was performed between 1100 and 1500 °C. Homoepitaxial growth of 6H‐SiC was achieved at temperatures as low as 1200 °C, utilizing step‐flow growth. Twinned crystalline 3C‐SiC was grown at 1100 °C; this result can be ascribed to suppressed surface migration of adsorbed Si species at the lower temperature, and to the occurrence of two‐dimensional nucleation on terraces. The C/Si ratio significantly effected the surface morphology and growth rate. The growth rate was limited by the supply of Si species, where the growth rate activation energy was very small (3.0 kcal/mol), and little difference in the growth rates on Si and C faces was observed. The quantitative analysis revealed that growth of 6H‐SiC in step‐controlled epitaxy is controlled by the diffusion of reactants in a stagnant layer.

Solid-State Phase Transformation in Cubic Silicon Carbide

The thermal stability of single crystalline 3C-SiC was investigated at temperatures from 1800 to 2400°C in an Ar atmosphere, and a solid-state phase transformation from 3C-SiC to 6H-SiC was observed above 2150°C. Single crystals of 3C-SiC(100) grown on Si(100) were used as starting crystals after removing Si. Annealings were carried out with changing temperature, pressure and time. The change in the Si/C composition ratio of annealed samples was determined by Auger electron analysis. The polytypes of samples were examined by photoluminescence, Raman scattering, X-ray diffraction and reflection high-energy electron diffraction before and after annealing. The spatial distribution and depth profile of the phase-transformed 6H-SiC region in annealed samples were observed by means of Raman microscopy. The mechanism of 3C→6H phase transformation in SiC is discussed.

Polytype‐controlled single‐crystal growth of silicon carbide using 3C→6H solid‐state phase transformation

The phase transformation from 3C‐SiC to 6H‐SiC at high temperature has been applied to crystal growth of SiC. Single‐crystal growth of controlled polytype has been carried out on chemical‐vapor‐deposition‐grown 3C‐SiC(001) films by using a sublimation method. The polytype of grown layers was controlled as either cubic 3C‐SiC or hexagonal 6H‐SiC. The growth temperature was varied in the range of 1800–2400 °C. A growth rate up to several hundred micrometers per hour was achieved. The polytypes, crystallographic planes, and crystallinity of the grown layers were examined using photoluminescence, Raman spectroscopy, x‐ray diffraction, reflection high‐energy electron diffraction, and molten KOH (potassium hydroxide) etching. The polytype of the grown layers was changed from 3C‐SiC to 6H‐SiC with an increase in substrate temperature, and 6H‐SiC(0114) planes were grown on 3C‐SiC(001) at high temperatures. The crystallographic relationship between 6H‐SiC(0114) and 3C‐SiC(001) is described. The growth mechanism o...

Bulk crystal growth of 6H-SiC on polytype-controlled substrates through vapor phase and characterization

Abstract Bulk crystal growth of 6H-SiC was carried out by a sublimation method in the temperature range of 2000–2400°C. The pressure was varied from 1 to 760 Torr. As a substrate, polytype-controlled 6H-SiC(01 1 4) grown on 3C-SiC(001) was used. A growth rate as high as 6 mm/h was obtained. Bulk single crystals of 6H-SiC(01 1 4) up to 25 mm in diameter and 12 mm in length were grown in 6 h. The polytypes and crystallinity of the grown layers were examined by optical transmission spectroscopy, photoluminescence, X-ray diffraction and etch-pits observation. The electrical properties of the bulk crystals were characterized by Hall measurements.

Phonon‐electron scattering in single crystal silicon carbide

We have measured the thermal conductivity κ of single crystals of hexagonal silicon carbide (6H‐SiC) of two different electron densities n. The densities are low such that virtually all of the heat is conducted by lattice vibrations. At low temperatures the thermal conductivity of both samples varies as T2 and scales with the electron density. The calculated phonon mean free path thus varies as T−1 and is consistent with a model of scattering of the heat‐carrying phonons by electrons in an impurity band.

Single crystal growth of hexagonal SiC on cubic SiC by intentional polytype control

Crystal growth of SiC on 3C-SiC(100) substrates has been carried out by using a sublimation method, utilizing the phase transformation from cubic 3C-SiC to hexagonal 6H-SiC at high temperatures. Polytype control in SiC growth on CVD-grown 3C-SiC(100) substrates was successfully achieved for the first time. The growth rate was several hundred microns per hour. The polytypes and crystallographic planes of the grown layers were examined using photoluminescence, Raman spectroscopy, X-ray diffraction and RHEED analyses. The polytypes of the grown layers change from cubic 3C modification to hexagonal 6H modification with increase in temperature. 6H-SiC with (0114) planes can be grown on 3C-SiC(100). Ingots of 6H-SiC up to 15 mm in diameter and 6 mm in length were grown in 6 h. The grown mechanism of 6H-SiC on 3C-SiC substrates based on the experimental results is discussed.

Homoepitaxial Chemical Vapor Deposition of 6H–SiC at Low Temperatures on {01\bar14} Substrates

Homoepitaxial chemical vapor deposition of 6H-SiC at low temperatures on {014} substrates has been investigated. The crystal growth was carried out using a SiH4-C3H8-H2 system in the temperature range of 1000~1500°C. Crystallinity of grown layers was characterized by means of reflection high-energy electron diffraction and etch-pit observation. The influences of surface polarity and growth conditions on crystallinity of grown layers were investigated. Significant effects of C/Si ratio on the growth were observed. Homoepitaxial growth of 6H-SiC was realized on (01)C-face substrates at temperatures as low as 1100°C, which is 700°C lower than that on {0001} basal planes.

Interface structures of epitaxial β-SiC on α-SiC substrates

Abstract Epitaxial β-SiC (3C) films were grown on (0001) 6H-SiC and 15R-SiC substrates by chemical vapor deposition (CVD). Transmission electron microscopy (TEM) characterization revealed that both films exhibited large areas of atomically flat, coherent interfaces. These areas were sometimes separated by structural ledges that were integral numbers of α-SiC unit cells in height. When 3C-SiC films were grown on 6H substrates, the primary defects were double position boundaries (DPBs), and islands of 6H were occasionally embedded in the predominantly 3C film. Films of 3C-SiC grown on 15R substrates exhibited relatively few grain boundaries, although islands of 15R were sometimes observed. The effect of substrate surface terraces on the observed interfacial microstructures and on defect formation mechanisms is discussed.

Photoluminescence of Ti doped 6H-SiC grown by vapor phase epitaxy

Sharp luminescence peaks near the bandgap have been observed in 6H-SiC epitaxial films doped with Ti. The intensity of the Ti-related peak increases with the increase of Ti concentration in the films. The peak energy of the zero-phonon line (2.864 eV) is independent of both excitation intensity and temperature. Above results reveal that the luminescence lines are attributed to exciton recombination bound to Ti atoms and its phonon replicas.

Lattice mismatch measurement of epitaxial β‐SiC on α‐SiC substrates

The lattice mismatch in chemically vapor deposited epitaxial β‐SiC (3C‐SiC) films on 6H‐ and 15R‐SiC (0001) substrates was investigated using a high‐resolution x‐ray diffractometer. The misfit parallel and perpendicular to the growth plane was determined to be (Δc/c)∥=−9.3×10−4 and (Δa/a)⊥=1.9×10−4 for the 3C/6H system, and (Δc/c)∥=−10.0×10−4 and (Δa/a)⊥=2.3×10−4 for the 3C/15R system. Our analysis of the lattice parameters in these three SiC polytypes revealed that the Si‐C pair spacings along the c direction increased with substrate hexagonality, while the lattice spacings along the a direction decreased with hexagonality. The extent of relaxation was greater in 3C films grown on 6H substrates, a phenomenon attributed to a higher density of double position boundaries.