Papers by Keyword: 15R-SiC

Abstract: The electronic quality of a Physical Vapour Transport (PVT) grown 15R-SiC crystal at different stages of growth was assessed by time-resolved optical pump-probe techniques. The measured differential transmittivity (DT) kinetics for the layers corresponding to the initial, middle and final stages of growth revealed clear differences in the decay of the DT signal, indicating a decreasing concentration of traps at the later stages of the crystal growth. The estimated trap concentration in the initial layer was N_T ≈ 10¹⁹ cm^-3, while it decreased down to less than 2×10¹⁸ cm^-3 in the top layer. The injection dependence of the diffusion coefficient at room temperature confirmed the gradual decrease of N_T in the layers corresponding to later stages of growth. Accordingly, the bipolar diffusion coefficient in the middle and the top layer was D_a ≈ 2 cm²/s, while D_a = 0.9 cm²/s was measured in the layer closest to the seed.

Abstract: We report on the stabilization of 15R Silicon Carbide (15R-SiC) grown by seeded sublimation method. It was found that polytype transitions are directly related to the occurrence of facets on the grown crystals. Once a foreign polytype is formed, its propagation is governed mainly by the interface shape of the crystal and its evolution during growth. A concave crystal shape enhances the expansion of foreign polytypes, usually formed at the periphery of the crystal. Then, foreign polytypes can either overlap the original polytypes (constant concave crystal shape) or form inclusions (change to convex crystal shape). On the contrary, an initially slightly convex interface repels foreign polytypes towards the edge of the crystal. The optimization of the growth interface shape can be a key issue towards the stabilization of bulk 15R-SiC crystals.

Abstract: To study the geometrical and electronic structure of 15R-SiC polytypes, the lattice parameter, band structure, density of states (DOS) and charge density of 15R-SiC are calculated by using density functional theory based on the plane wave pseudopotential approach, and electronic structure and ground properties of 15R-SiC are investigated by the calculated band structure and DOS, the results show that 15R-SiC is an indirect band gap semiconductor, with calculated indirect band gap width being 2.16 eV and band gap dependent on Si 3p and C 2p states. While charge density results show that Si-C bond is a hybrid bond semiconductor strong in covalent bond and weak in ionicity, characterized by intense sp³ hybrid characteristics, which is in accordance with the experimental results. The above mentioned results are considered as theoretical reference for design and application of SiC polytype materials.

Abstract: We present experimental results with regard to the evaluation of growth-induced polytype domains in 6H-SiC crystals grown by sublimation method and these domains are characterized by using the polarized optical microscopy and micro-Raman spectroscopy. The polytype domains of reverse triangular are generated by local variation of temperature along cdirection and spread-wing shapes normally occurred forming micropipes in many cases. These polytype domains may be generated due to the local variation of supersaturation and/or temperature at central position during crystal growth. In this work, we try to elucidate the origin and mechanism responsible for growth-induced polytype domains.