다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Wide bandgap semiconductors show superior material properties enabling potential power device operation at higher temperatures, voltages, and switching speeds than current Si technology. As a result, a new generation of power devices is being developed for power converter applications in which traditional Si power devices show limited operation. The use of these new power semiconductor devices will allow both an important improvement in the performance of existing power converters and the development of new power converters, accounting for an increase in the efficiency of the electric energy transformations and a more rational use of the electric energy. At present, SiC and GaN are the more promising semiconductor materials for these new power devices as a consequence of their outstanding properties, commercial availability of starting material, and maturity of their technological processes. This paper presents a review of recent progresses in the development of SiC- and GaN-based power semiconductor devices together with an overall view of the state of the art of this new device generation.

A Survey of Wide Bandgap Power Semiconductor Devices

Light-Emitting Diodes. (Monographs in Electrical and Electronic Engineering.) By A. A. Bergh and P. J. Dean. Pp. viii+591. (Clarendon: Oxford; Oxford University: London, 1976.) £22.

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Light-emitting diodes

An object is to provide a semiconductor device of which a manufacturing process is not complicated and by which cost can be suppressed, by forming a thin film transistor using an oxide semiconductor film typified by zinc oxide, and a manufacturing method thereof. For the semiconductor device, a gate electrode is formed over a substrate; a gate insulating film is formed covering the gate electrode; an oxide semiconductor film is formed over the gate insulating film; and a first conductive film and a second conductive film are formed over the oxide semiconductor film. The oxide semiconductor film has at least a crystallized region in a channel region.

Semiconductor device, and manufacturing method thereof

Through recent progress in SiC technology, 1–3 kV-class SiC power devices (field effect transistors and Schottky barrier diodes) have been commercialized, demonstrating remarkable reduction of power dissipation in various electric systems. However, “bipolar degradation” caused by forward conduction of pn junctions has not been completely solved [1]. In this paper, physical understanding and prevention of the bipolar degradation in SiC devices are reviewed.
 Degradation in SiC bipolar devices is caused by expansion of a single Shockley-type stacking fault (SSF) in {0001} from a basal plane dislocation (dislocations lying on a {0001} plane) through minority carrier injection and subsequent recombination [2]. The authors conducted careful observation and theoretical analyses on the shapes of expanded SSFs in SiC upon minority carrier injection, and clarified 36 different types of SSFs [3]. For fabrication of high-reliability SiC devices, any basal plane dislocations must be eliminated from a lightly-doped voltage-blocking layer, where a high density of excess carriers is injected during device operation. The authors carried out a number of SiC epitaxial growth runs by using a custom-made chemical vapor deposition system and discovered that almost all the basal plane dislocations can be converted to threading edge dislocations in the initial stage of SiC epitaxial growth (dislocation conversion occurs near the epilayer/substrate interface). The typical density of basal plane dislocations in SiC epitaxial layers was 1–10 cm-2, but the density could be reduced to 0.1 cm-2 or less by increasing the growth rate from 5 to 24 µm/h on 4 degrees off-axis SiC(0001) substrates without any conflicts in the surface morphology and doping control (see the attached image). The achieved dislocation density (< 0.1 cm-2) is low enough to fabricate 1 cm2 devices (300–400 A devices) free from the degradation phenomenon. A basal plane dislocation and a threading edge dislocation can possess the same Burgers vector, which is the reason why the dislocation conversion can take place. It is also noted that a threading edge dislocation, which runs along <0001> (perpendicular to the {0001} plane), does not affect the performance and reliability of SiC devices, at least, within operation conditions in practical applications.
 It has been experimentally revealed that a SSF can either expand or contract, depending on the current density and temperature. Thus, it is essential to clarify the critical condition where SSF expansion starts. The authors developed a physics-based model to calculate the effective formation energy of a SSF in SiC, taking account of the electronic energy gain by forming a SSF under minority carrier injection [4]. Here a SSF exhibits a slightly smaller bandgap than the perfect SiC and a SSF behaves like a quasi-quantum well in SiC. It can be judged that SSF expansion takes place when the effective SSF formation energy is negative, by which the free energy is lowered by SSF expansion [5].
 The effective SSF formation energy was calculated as a function of the injected excess carrier density at different temperatures. When the carrier density is low, the SSF formation energy is close to the value in equilibrium (4.7 mJ/m2 [6]). As the carrier density increases, the SSF formation energy turns to be negative due to the electronic energy gain, and the critical excess carrier density above which SSF expansion occurs can be determined as about 5E14 cm-3 at 300 K from this calculation. This critical carrier density gradually increases with elevating the temperature, due to the enhanced emission of electrons from an SSF and thereby a lowered energy gain. The critical carrier density was experimentally determined through observation of SSFs in fabricated SiC pn diodes operating at different current densities and temperatures. The critical carrier density experimentally determined was 4E14 cm-3 at room temperature, being a very good agreement with the theoretical prediction mentioned above. Therefore, the developed model serves as a guideline for preventing bipolar degradation. Based on these results, nearly perfect prevention of bipolar degradation can be achieved by introducing a “recombination-enhancement layer” between a voltage-blocking layer and a substrate, the detail of which shall be explained at the conference.
 [1] T. Kimoto and H. Watanabe, Appl. Phys. Express, 13, 120101 (2020).
 [2] M. Skowronski and S. Ha, J. Appl. Phys., 99, 011101 (2006).
 [3] A. Iijima et al., Philos. Mag., 97, 2736 (2017).
 [4] A. Iijima and T. Kimoto, J. Appl. Phys., 126, 105703 (2019).
 [5] K. Maeda et al., Mater. Sci. Forum, 725, 35 (2012).
 [6] K. Maeda et al., Appl. Phys. Express, 14, 044001 (2021).
 
 
 
 
 
 Figure 1


(Invited) Physical Understanding and Prevention of Bipolar Degradation in SiC Power Devices

Ultra-pure n-type (8×1013 cm-3), 99 μm thick epitaxial films of 4H SiC were electron irradiated at 170 keV with a fluence of 5×1016 cm-2 or at 1 MeV with a fluence of 1×1015 cm-2 in various geometries. Low temperature photoluminescence (LTPL) spectra and microwave photoconductance (μPCD) lifetime measurements were obtained on all samples prior to annealing and after annealing in Argon in free standing mode or on a POCO carbon platform, every 50°C from 1100°C to 1500°C. No improvement in carrier lifetime was obtained. Spurious lines attributable to the use of a Genesis CX 3550A laser are also reported.

Annealing of Electron Irradiated, Thick, Ultrapure 4H SiC between 1100°C and 1500°C and Measurements of Lifetime and Photoluminescence

We calculated the conduction band structure of GeNWs by a tight-binding model and obtained the fundamental understanding of electron transport characteristics in [001], [110], [111], and [112] GeNW FETs. The simulation of ballistic electron transport revealed that [110] GeNW FETs on the (001) face achieve high drive current as well as high injection velocity, being the best choice for n-channel FETs.

Orientation and size effects on ballistic electron transport properties in gate-all-around rectangular germanium nanowire FETs

The present tight-binding study of rectangular SiNWs along [001], [110], and [111] revealed that the hole m* of [001] and [110] NWs on the {001} basal face has strong dependence on the width. Because this nature may make the design of devices difficult, these NWs are considered to be unfavorable for p-channel devices. In contrast, rectangular [111] NWs on both (112) and (110) basal faces are favorable for p-channel devices because they have the smallest hole m* and its value is very resistant to the variability of the width.

Tsunenobu Kimoto

Papers

(Invited) Physical Understanding and Prevention of Bipolar Degradation in SiC Power Devices

Annealing of Electron Irradiated, Thick, Ultrapure 4H SiC between 1100°C and 1500°C and Measurements of Lifetime and Photoluminescence

Orientation and size effects on ballistic electron transport properties in gate-all-around rectangular germanium nanowire FETs

Tight-binding study of size and geometric effects on hole effective mass of silicon nanowires

High-Voltage SiC Power Devices for Energy Electronics