Papers by Keyword: 6H-SiC

Abstract: Carrier lifetimes in 6H-SiC epilayers were investigated by using numerical simulations and micro-wave photoconductivity decay measurements. The measured carrier lifetimes were significantly increasing with an increased thickness up to 200 μm while it stays almost constant in layers thicker than 200 μm. From a comparison of the simulation and experimental results, we found that if the bulk lifetime in 6H-SiC is around a few microseconds, both the surface recombination and interface recombination influence the carrier lifetime in layers with thickness less than 200 μm while only the surface recombination determines the carrier lifetime in layers with thickness more than 200 μm. In samples with varying thicknesses, a bulk lifetime = 2.93 μs and carrier diffusion coefficient D= 2.87 cm²/s were derived from the linear fitting of reciprocal lifetime vs reciprocal square thickness.

Abstract: The growth of homoepitaxial layers on off-oriented 6H-SiC substrates proceeds via step flow growth. Such epilayers can exhibit irregularities like step bunching, splicing or crossover of steps. The effects of the substrate off-orientation and growth temperature show an influence on formation of surface irregularities. The mean features seem to be given by the growth mode competition of two-dimensional growth to the step-flow growth.

Abstract: This paper describes the solution growth of SiC by a temperature difference method using an Fe-Si solvent. Crystal growth of SiC from an Fe-40 mol%Si solvent onto a seed wafer of 6H-SiC or 4H-SiC was carried out at 1623 – 1723 K under induction heating. Homo-epitaxial growth on both 6H-SiC and 4H-SiC was identified by Raman spectroscopy, and the SiC growth rate was found to be 90 – 260 μm/h. Experiments were also conducted under resistance heating at 1623 K using conditions which suppressed natural convection. Convective mass transfer in the solution was found to be important for rapid growth of SiC.

Abstract: The preparation and application of co-doped polycrystalline SiC as source in sublimation growth of fluorescent layers is a complex topic. Photoluminescence topographies of luminescent 6H-SiC layers and their corresponding source crystals have been studied in order to investigate the dependence of the epitaxial growth on the source material. It is shown that the homogeneity concerning the dopant incorporation and the layer luminescence intensity does not depend on the characteristics of the PVT grown source material. Therefore co-doped polycrystalline SiC is a promising source material in fast sublimation growth of luminescent 6H-SiC.

Abstract: Micro-Raman spectroscopy is an excellent non-destructive analysis method, which compensates for disadvantages of KOH method. Raman shift of A1(LO) and E1(TO) band at threading screw dislocation(TSD) were investigated in n-type on/off-axis 4H- and 6H-SiC single crystal wafers by Micro-Raman scattering at room temperature. The results showed that A1(LO) band were shifted toward higher frequency while the E1(TO) band were shifted toward lower frequency on the on-axis wafers. The shifts are caused by increasing electron concentration and lattice disorder near the dislocation core, respectively. In the off-axis wafers, no shifts were observed possibly due to the measurement geometry which does not contain whole dislocation core.

Abstract: High-resolution synchrotron radiation X-ray absorption of Si K-edge have been employed to investigate 6H-, 4H- and 3C-SiC. Detailed analyses of the extended x-ray absorption fine structure are taken by using the IFEFFIT program, and significant results on the atomic bonding are obtained from these comparative studies. The x-ray absorption near-edge structures of the Si K-edge are investigated, and the electronic structure of 3C-, 4H- and 6H-SiC are studied. In order to investigate the angular dependence, the x-ray absorption near-edge spectra were operated at 55o and 90o of the angle between the surface and the X-ray direction.

Abstract: The structural defects in the single 6H-SiC crystals grown by the PVT method have been studied by the scanning electron microscopy, Raman scattering and photoluminescence techniques. The formation mechanism of the defects, micropipes and parasitic polytypes 4H and 15R, observed in the single 6H-SiC crystal has been proposed.

Abstract: We have grown graphene on SiC(0001) using propane-hydrogen CVD. In this work, we present the effects of growth pressure and temperature on structural and electrical properties. Structural characterizations evidence the formation of graphene with in-plane rotational disorder, except for low growth pressure and high growth temperature which lead to the formation of a (6Ö3´6Ö3)-30° interface between graphene and SiC. Electrical properties of samples presenting different graphene/SiC stacking and interfaces are compared and discussed.

Abstract: We present epitaxial graphene (EG) growth on non-polar a-plane and m-plane 6H-SiC faces where material characterization is compared with that known for EG grown on polar faces. AFM surface morphology exhibits nanocrystalline graphite like features for non-polar faces, while polar silicon face shows step like features. This differing behavior is attributed to the lack of a hexagonal template on the non-polar faces. Non-polar faces also exhibit greater disorder and red shift of all Raman peaks (D, G and 2D) with increasing temperature. This is attributed to decreasing stress with increasing temperature. These variations provide evidence of different EG growth mechanisms on non-polar and polar faces, likely due to differences in surface free energy. We also present differences between a-plane ( ) EG and m-plane ( ) EG in terms of morphology, thickness and Raman characteristics.

Abstract: Nitrogen-boron doped 6H-SiC epilayers grown on low off-axis 6H-SiC substrates have been characterized by photoluminescence and Raman spectroscopy. The photoluminescence results show that a doping larger than 10¹⁸ cm^-3 is favorable to observe the luminescence and addition of nitrogen is resulting in an increased luminescence. A dopant concentration difference larger than 4x10¹⁸ cm^-3 is proposed to achieve intense photoluminescence. Raman spectroscopy further confirmed the doping type and concentrations for the samples. The results indicate that N-B doped SiC is being a good wavelength converter in white LEDs applications.