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•We observed carrier lifetimes from the angle-lapped SrTiO3 with the (100), (110) and (111) faces.•We analyzed for dependence of the carrier lifetimes on the thickness of the ...angle-lapped SrTiO3.•We obtained accurate surface recombination velocities and bulk carrier lifetimes for SrTiO3.
Strontium titanate (SrTiO3) is a promising photocatalyst for solar-to-hydrogen conversions. The carrier lifetime τ dominates the energy conversion efficiency in photocatalysts, and the surface recombination velocities Ss have significant effects on τ. To estimate Ss for the (100), (110), and (111) faces of SrTiO3, we employed samples with angle-lapped structures. The microwave photoconductivity decay method was adopted for the measurements, and the thickness dependence of τ was analyzed. Consequently, we obtained a more accurate Ss compared to that obtained in a previous study. We also observed differences in bulk τ among the samples, and this difference reflects the crystalline quality.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In recent years, 4H-SiC power devices have been widely employed in power electronic systems owing to their superior performance to Si power devices. However, stacking faults in 4H-SiC can degrade the ...device performance. Stacking faults can be considered as polytype inclusions in 4H-SiC. Carrier recombination in stacking faults is considered a cause for performance degradation. Understanding carrier recombination in different polytypes other than 4H-SiC can be helpful in understanding the mechanism of performance degradation due to stacking faults in 4H-SiC. Therefore, in this study, we characterized the recombination coefficients of 3C- and 6H-SiC and compared them with those of 4H-SiC using the time-resolved free-carrier absorption measurement method. Recombination at the stacking faults in 4H-SiC cannot be considered as the intrinsic recombination of inclusions of other polytypes.
Abstract
SiC bipolar degradation, which is caused by stacking fault expansion from basal plane dislocations in a SiC epitaxial layer or near the interface between the epitaxial layer and the ...substrate, is one of the critical problems inhibiting widespread usage of high-voltage SiC bipolar devices. In the present study, we investigated the stacking fault expansion behavior under UV illumination in a 4H-SiC epitaxial layer subjected to proton irradiation. X-ray topography observations revealed that proton irradiation suppressed stacking fault expansion. Excess carrier lifetime measurements showed that stacking fault expansion was suppressed in 4H-SiC epitaxial layers with proton irradiation at a fluence of 1 × 10
11
cm
−2
without evident reduction of the excess carrier lifetime. Furthermore, stacking fault expansion was also suppressed even after high-temperature annealing to recover the excess carrier lifetime. These results implied that passivation of dislocation cores by protons hinders recombination-enhanced dislocation glide motion under UV illumination.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Silicon carbide (SiC) is a chemically stable and photocatalytic semiconductor material. Among SiC polytypes, 3C-SiC has the smallest band gap (2.3 eV), and thus 3C-SiC is capable to absorb a ...significant part of solar light. The use of p-type semiconductor as photocathode reduces hydrogen in water. Cathodic operation prevents oxidation of photocatalytic materials. Therefore p-type 3C-SiC will be an efficient and durable photocatalyst. Our experiments have revealed that p-type 3C-SiC acts as photocathodes with excellent performance. Solar to hydrogen conversion efficiency for p-type 3C-SiC photocathodes with Pt cocatalysts was 0.52 %. Considering such a high efficiency and possibility of further improvement, SiC is a very promising material for the solar to hydrogen conversion technology.
Abstract
4H-SiC has been commercialized as a material for power semiconductor devices. However, the long-term reliability of 4H-SiC devices is a barrier to their widespread application, and the most ...important reliability issue in 4H-SiC devices is bipolar degradation. This degradation is caused by the expansion of single Shockley stacking-faults (1SSFs) from basal plane dislocations in the 4H-SiC crystal. Here, we present a method for suppressing the 1SSF expansion by proton implantation on a 4H-SiC epitaxial wafer. PiN diodes fabricated on a proton-implanted wafer show current–voltage characteristics similar to those of PiN diodes without proton implantation. In contrast, the expansion of 1SSFs is effectively suppressed in PiN diodes with proton implantation. Therefore, proton implantation into 4H-SiC epitaxial wafers is an effective method for suppressing bipolar degradation in 4H-SiC power-semiconductor devices while maintaining device performance. This result contributes to the development of highly reliable 4H-SiC devices.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The white-rot fungus Phanerochaete chrysosporium can degrade lignin polymers using extracellular, non-specific, one-electron oxidizing enzymes. This results in the formation of guaiacyl (G), syringyl ...(S), and hydroxyphenyl (H) units, such as vanillic acid, syringic acid, and p-hydroxybenzoic acid (p-HBA) and the corresponding aldehydes, which are further metabolized intracellularly. Therefore, the aim of this study was to identify proteins involved in the hydroxylation of H-unit fragments such as p-HBA and its decarboxylated product hydroquinone (HQ) in P. chrysosporium. A flavoprotein monooxygenase (FPMO), PcFPMO2, was identified and its activity was characterized. Recombinant PcFPMO2 with an N-terminal polyhistidine tag was produced in Escherichia coli and purified. In the presence of NADPH, PcFPMO2 used six phenolic compounds as substrates. PcFPMO2 catalyzed the hydroxylation of the H-unit fragments such as p-HBA and HQ, and the G-unit derivative methoxyhydroquinone (MHQ). The highest catalytic efficiency (kcat/Km) was observed with HQ, indicating that PcFPMO2 could be involved in HQ hydroxylation in vivo. Additionally, PcFPMO2 converted MHQ to 3-, 5-, and 6-methoxy-1,2,4-trihydroxybenzene (3-, 5-, and 6-MTHB), respectively, suggesting that PcFPMO2 might partially be involved in MHQ degradation, following aromatic ring fission, via three MTHBs. FPMOs are divided into eight groups (groups A to H). This is the first study to show MHQ hydroxylase activity of a FPMO-group A superfamily member. These findings highlight the unique substrate spectrum of PcFPMO2, making it an attractive candidate for biotechnological applications.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
We characterized the photocatalytic performance of rutile TiO2 single crystals with Nb doping (0.01-0.05 wt%) for water splitting and then observed the effects of doping. Although Nb doping induces ...additional optical absorption below the bandgap energy, it does not contribute to photocatalytic performance. Moreover, Nb doping enhances carrier recombination and donor concentration, resulting in reduction of the hole diffusion length and depletion of the layer width. Furthermore, it reduces the existing holes generated by light for photocatalysis because of the difficulty of charge separation by an internal electric field. In addition, comparison of the theoretically calculated photocurrents indicates that high Nb doping has other negative effects on the photocatalytic performance. These results suggest that, although Nb doping enhances the electrical conduction by increasing the donor concentration, it has negative effects on other important characteristics for photocatalysis. Therefore, Nb doping has optimum concentrations depending on structures of the photoelectrode.
