In bipolar SiC devices, which are promising under ultra-high voltage operation, the carrier lifetime is a highly influential parameter for the device performance. Surface recombination is one of the limiting factors for the carrier lifetime, and quantitative values of the surface recombination velocities are required for the design and development of fabrication processes of the devices. In this study, we observe carrier recombination at various temperatures for the Si- and C-faces of n- and p-type 4H-SiC samples and the a- and m-faces of n-type 4H-SiC samples with a treatment of chemical mechanical polishing or reactive ion etching by using the microwave photoconductivity decay method. From the experimental results, we estimate surface recombination velocities and bulk carrier lifetimes of the samples by using an analytical model. As a result, we found the smallest surface recombination velocity of 150 cm/s for the chemical mechanical polished surface of the Si-face of the n-type samples at room temperature. Surface recombination velocities increased with temperature for the chemical mechanical polished surfaces. The surfaces treated with reactive ion etching showed relatively large surface recombination velocities with weak temperature dependence. Based on these results, we discuss the origins of the recombination centers at surfaces of 4H-SiC.

Phase-separated conetwork structure was induced by a radical copolymerization of telechelic polymer, (polydimethylsiloxane-α,ω-diacrylate (PDMS-DA)), and N,N-dimethylacrylamide (DMAA). The structure development was investigated by in situ SAXS measurement. A mixture of PDMS-DA and DMAA was transparent and homogeneous and gave no peak in SAXS profile. The radical copolymerization of both initiated at 303−363 K was successfully done to form fully transparent objects. Peak was observed in SAXS from the resulting polymer, which can be interpreted in terms of Teubner−Stray model, involving a polymer morphology with given a periodicity. The analysis of time evolution of the SAXS profiles (in site measurement) revealed that the phase separation occurred via the spinodal decomposition mechanism. The morphology was fixed by solidification of the sample due to cross-linking and glass transition during reaction-induced phase separation. The final structure was interpreted fairly using Teubner−Stray model. Thus, the final structure of the PDMS-DA/DMAA copolymer sample was found to be a bicontinuous and periodic structure (conetwork) in nanometer scale. The structure was also confirmed by TEM.

Magnesium-promoted reductive introduction of a trifluoroacetyl group to coumarin in the presence of ethyl trifluoroacetate and the subsequent treatment with trifluoroacetic acid led to simple access to a trifluoromethylated benzofurofuranone at 8a-position with a high regio-and stereoselectivity. Trifluoromethylated or difluoromethylated benzofurofuranone derivatives were also prepared from coumarins including naturally occurring ones only in two successive steps, which might have potential bioactivity in medicinal chemistry.

In the development of 4H‐SiC bipolar devices, defect generation during the fabrication process is an important issue for maintaining a long carrier lifetime in the drift layers. Herein, two 4H‐SiC PiN diode structures are produced with a p‐type layer fabricated through epitaxial growth or Al ion implantation; and the current–voltage characteristics and defect distribution observed using deep‐level transient spectroscopy and cathodoluminescence (CL) are compared. The PiN diode fabricated through ion implantation shows higher deep‐level concentrations even at a drift layer depth of ≈6 μm from the junction. In addition, the concentrations at the deep levels decrease with the depth, as does the CL intensity originating from defects. Therefore, defects induced through Al‐ion implantation are distributed into a drift layer with a gradual decrease in the concentration along the depth. These results suggest that drift layers in 4H‐SiC bipolar devices should be fabricated in regions far from the Al‐ion‐implanted regions to induce an efficient conductivity modulation.

Si ion implantation was widely used to synthesize specimens of SiO 2 containing supersaturated Si and subsequent high temperature annealing induces the formation of embedded luminescent Si nanocrystals. In this work, the potentialities of excimer UV-light (172 nm, 7.2 eV) irradiation and rapid thermal annealing (RTA) to enhance the photoluminescence and achieve low temperature (below 1000 o C) formation of Si nanocrystals have been investigated. The Si ions were introduced at acceleration energy of 180 keV to fluence of 7.5 x 10 16 ions/cm 2. The implanted samples were subsequently irradiated with a excimer-UV lamp. After the process, the samples were rapidly thermal annealed before furnace annealing (FA). Photoluminescence spectra were measured at various stages at the process. We found that the luminescence intensity is strongly enhanced with excimer-UV irradiation and RTA prior to conventional FA at 1050 o C. Moreover, effective visible photoluminescence is found to be observed even after FA at 900 o C, only for specimens treated with excimer-UV lamp and RTA, prior to a low temperature FA process. Based on our experimental results, we discuss the effects of excimer-UV lamp irradiation and RTA process on the luminescence.