- 标题
- 摘要
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- 实验方案
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Use of 1.7 kV and 3.3 kV SiC Diodes in Si-IGBT/ SiC Hybrid Technology
摘要： Replacing conventional Si diodes with SiC diodes in Si insulated gate bipolar transistor (IGBT) modules is advantageous as it can reduce power losses significantly. Also, the fast switching nature of the SiC diode will allow Si IGBTs to operate at their full high-switching-speed potential, which at present conventional Si diodes cannot do. In this work, the electrical test results for Si-IGBT/4H-SiC-Schottky hybrid substrates (hybrid SiC substrates) are presented. These substrates are built for two voltage ratings, 1.7 kV and 3.3 kV. Comparisons of the 1.7 kV and the 3.3 kV Si-IGBT/Si-diode substrates (Si substrates) at room temperature (20 ?C, RT) and high temperature (125 ?C, HT) have shown that the switching losses in hybrid SiC substrates are miniscule as compared to those in Si substrates but necessary steps are required to mitigate the ringing observed in the current waveforms. Also, the effect of design variations on the electrical performance of 1.7 kV, 50 A diodes is reported here. These variations are made in the active and termination regions of the device.
关键词： Hybrid substrates,Switching losses,IGBT,JTE and FLRs,Schottky diode,SiC
更新于2025-09-23 15:21:01
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[Advances in Experimental Medicine and Biology] || Photoresponsive Hydrogels with Photoswitchable Stiffness: Emerging Platforms to Study Temporal Aspects of Mesenchymal Stem Cell Responses to Extracellular Stiffness Regulation
摘要： An extensive number of cell-matrix interaction studies have identi?ed matrix stiffness as a potent regulator of cellular properties and behaviours. Perhaps most notably, matrix stiffness has been demonstrated to regulate mesenchymal stem cell (MSC) phenotype and lineage commitment. Given the therapeutic potential for MSCs in regenerative medicine, signi?cant efforts have been made to understand the molecular mechanisms involved in stiffness regulation. These efforts have predominantly focused on using stiffness-de?ned polyacrylamide (PA) hydrogels to culture cells in 2D and have enabled elucidation of a number of mechano-sensitive signalling pathways. However, despite proving to be a valuable tool, these stiffness-de?ned hydrogels do not re?ect the dynamic nature of living tissues, which are subject to continuous remodelling during processes such as development, ageing, disease and regeneration. Therefore, in order to study temporal aspects of stiffness regulation, researchers have developed and exploited novel hydrogel substrates with in situ tuneable stiffness. In particular, photoresponsive hydrogels with photoswitchable stiffness are emerging as exciting platforms to study MSC responses to extracellular stiffness regulation. This chapter provides an introduction to the use of PA hydrogel substrates, the molecular mechanisms of mechanotransduction currently under investigation and the development of these emerging photoresponsive hydrogel platforms.
关键词： Photoswitchable stiffness,Biophysical regulation,Photoresponsive,Cell-matrix interaction,Regenerative medicine,Polyacrylamide,Mechanotransduction,Stiffness regulation,Mesenchymal stem cells,Cell adhesion,Temporal,Hydrogel substrates
更新于2025-09-23 15:21:01
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Laser firing in silicon heterojunction interdigitated back contact architecture for low contact resistance
摘要： This work reports a laser firing technique applied to completed silicon heterojunction interdigitated back contact solar cells in order to lower contact resistance. Previously, the implementation of a-Si:H(i) at the electron contact of polycrystalline silicon solar cells on glass substrates led to an increase in series resistance. The cell architecture with the current record efficiency of 14.2% (with illumination through glass) utilizes only an a-Si:H(nt) layer (cid:0) 2 of short circuit current density is lost due to electrical shading under the electron contact and 2–2.9 mA cm [1,2]. The goal of implementing an a-Si:H(i) layer and laser firing at this contact is to achieve low contact resistance at fired spots while preserving a-Si:H(i) passivation in unfired regions. After the laser firing, VOC was (cid:0) 2 loss in JSC. In the best retained, while up to 14% absolute increase in FF was obtained with a mere 0.2 mA cm (cid:0) 2 loss in JSC. Two laser sources were used to first performing cell, a 72.1% FF was achieved with a 0.7 mA cm ablate a part of the silver contact metal, and then to laser fire through the Si(n)/a-Si:H(i/nt)/ITO/Ag contact. (cid:0) 2 (355 nm, picosecond pulse duration) and The optimal laser fluence was found to be 1.1–0.5 J cm (cid:0) 2 (532 nm, nanosecond pulse duration), respectively. The upper limit on specific contact resistance 4.4–5.2 J cm in the laser fired spots was calculated to be 38 ? 20 mΩcm2 as a conservative estimate.
关键词： Liquid phase crystallized silicon,Passivation,Interdigitated back contact,Foreign substrates,Laser fired contacts,Silicon heterojunction
更新于2025-09-23 15:19:57
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GaAs solar cells grown on intentionally contaminated GaAs substrates
摘要： III-V materials such as GaAs and GaInP have some of the best electronic and optical properties of any semiconductor materials, but deposition of these materials relies on high-quality single crystal GaAs substrates for their superior performance. Unfortunately, the cost of these substrates makes these high-efficiency devices only accessible in high-value or niche markets. Here, we explore the effect of growing bulk GaAs crystals with lower purity input materials in order to reduce their cost. We observe that intentional impurities added to the melt before the crystal growth occurs segregate to the top of the boule. Single junction GaAs solar cells grown on substrates made from contaminated boules showed no performance degradation compared to a high-purity control substrate. These results suggest that lower purity Ga and As source materials can be used during crystal growth to reduce the cost of substrates.
关键词： B2. Semiconducting III-V materials,A2. Gradient freeze technique,A1.Substrates,B3. Solar Cells
更新于2025-09-23 15:19:57
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Near full light absorption and full charge collection in 1-micron thick quantum dot photodetector using intercalated graphene monolayer electrodes
摘要： Quantum dots (QDs) offer several advantages in optoelectronics such as easy solution processing, strong light absorption and size tunable direct bandgap. However, their major limitation is their poor film mobility and short diffusion length (<250 nm). This has restricted the thickness of QD film to ～200–300 nm due to the restriction that the diffusion length imposes on film thickness in order to keep efficient charge collection. Such thin films result in a significant decrease in quantum efficiency for λ > 700 nm in QDs photodetector and photovoltaic devices, causing a reduced photoresponsivity and a poor absorption towards the near-infrared part of the sunlight spectrum. Herein, we demonstrate 1 μm thick QDs photodetectors with intercalated graphene charge collectors that avoid the significant drop of quantum efficiency towards λ > 700 nm observed in most QD optoelectronic devices. The 1 μm thick intercalated QD films ensure strong light absorption while keeping efficient charge extraction with a quantum efficiency of 90%–70% from λ = 600 nm to 950 nm using intercalated graphene layers as charge collectors with interspacing distance of 100 nm. We demonstrate that the effect of graphene on light absorption is minimal. We achieve a time-modulation response of <1 s. We demonstrate that this technology can be implemented on flexible PET substrates, showing 70% of the original performance after 1000 times bending test. This system provides a novel approach towards high-performance photodetection and high conversion photovoltaic efficiency with quantum dots and on flexible substrates.
关键词： Optoelectronics,Photodetectors,Quantum dots,Graphene,Flexible substrates
更新于2025-09-23 15:19:57
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Orientational competition in quantum dot growth in Si-Ge heteroepitaxy on pit-patterned Si(001) substrates
摘要： Towards precisely controlled nanostructure growth, patterned substrates are used as templates to direct heteroepitaxial self–assembly. This affects the size, shape and ordering of nanostructures which are formed as a consequence of the mismatch strain. In the well–studied case of Si–Ge heteroepiaxy on Si, the lattice mismatch leads to spontaneous formation of quantum dots. On patterned substrates, the competition between the length scale of the pattern and the intrinsic quantum dot size leads to rich behavior where the localization of dots can be modi?ed with respect to the features of the patterns. We show by continuum modeling that, in cubic elastic materials such as silicon and germanium, there is also a competition between the pattern orientation and the elastically soft directions of the ?lm which affects the precise location of quantum dots on the surface. When the pattern is between the elastically soft directions, the quantum dots can form purely in the narrow region directly between two neighboring pits, referred to as the saddle region. On the other hand, when the pattern is along the elastically soft directions, the quantum dots prefer to form in the region at the centre of four pits, referred to as the crown region. This resolves a discrepancy between theory and experiments and gives another dimension to control quantum dot formation in strained nanocrystalline systems.
关键词： elastic anisotropy,Si–Ge,quantum dots,patterned substrates,heteroepitaxy
更新于2025-09-23 15:19:57
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An Improved Room-Temperature Silicon Terahertz Photodetector on Sapphire Substrates
摘要： We design and fabricate a good performance silicon photoconductive terahertz detector on sapphire substrates at room temperature. The best voltage responsivity of the detector is 6679 V/W at frequency 300 GHz as well as low voltage noise of 3.8 nV/Hz1/2 for noise equivalent power 0.57 pW/Hz1/2. The measured response time of the device is about 9 ??s, demonstrating that the detector has a speed of >110 kHz. The achieved good performance, together with large detector size (acceptance area is 3 ??m×160 ??m), simple structure, easy manufacturing method, compatibility with mature silicon technology, and suitability for large-scale fabrication of imaging arrays provide a promising approach to the development of sensitive terahertz room-temperature detectors.
关键词： terahertz,room-temperature,sapphire substrates,silicon,photodetector
更新于2025-09-23 15:19:57
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High-Performance Germanium Waveguide Photodetectors on Silicon
摘要： Germanium waveguide photodetectors with 4 ??m widths and various lengths are fabricated on silicon-on-insulator substrates by selective epitaxial growth. The dependence of the germanium layer length on the responsivity and bandwidth of the photodetectors is studied. The optimal length of the germanium layer to achieve high bandwidth is found to be approximately 8 ??m. For the 4 × 8 ??m2 photodetector, the dark current density is as low as 5 mA/cm2 at ?1 V. At a bias of ?1 V, the 1550 nm optical responsivity is as high as 0.82 A/W. Bandwidth as high as 29 GHz is obtained at ?4 V. Clear opened eye diagrams at 50 Gbits/s are demonstrated at 1550 nm.
关键词： responsivity,Germanium waveguide photodetectors,silicon-on-insulator substrates,selective epitaxial growth,bandwidth
更新于2025-09-23 15:19:57
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[Laser Institute of America ICALEO?? 2014: 33rd International Congress on Laser Materials Processing, Laser Microprocessing and Nanomanufacturing - San Diego, California, USA (October 19a??23, 2014)] International Congress on Applications of Lasers & Electro-Optics - Laser ablation cutting of thin silicon subtrates with tunable ultra-short pulsed lasers from 200FS-10PS
摘要： In this paper the influence of the pulse duration in a range of 200 fs up to 10 ps on the cutting process of thin silicon is investigated. The experiments are carried out with a Light Conversion Pharos with various pulse duration between 190 fs and 10 ps. The laser is operated at the second harmonic wavelength of 515 nm and a repetition rate of 200 kHz. Although the ablation threshold, which is determined with the method of Liu [1], amounts 0.27 J/cm2 for 0.2, 1 and 10 ps, one can find extremely different ablation behavior during the cutting experiments. It turns out that independent from pulse energy and pulse overlap the shortest pulse duration at 200 fs leads to a deeper cutting depth and furthermore to a higher cutting speed. This difference can be explained with higher pulse peak intensities and shorter interaction time between laser and material for the 200 fs pulse duration. Nevertheless the general ablation geometry is very similar for all tested pulse durations. We explain this with a simple geometric model. This model considers the projection from a Gaussian beam profile in an existing cutting kerf.
关键词： cutting process,laser ablation,ultra-short pulsed lasers,pulse duration,thin silicon substrates
更新于2025-09-23 15:19:57
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Fermi velocity renormalization in graphene probed by terahertz time-domain spectroscopy
摘要： We demonstrate terahertz time-domain spectroscopy (THz-TDS) to be an accurate, rapid and scalable method to probe the interaction-induced Fermi velocity renormalization νF* of charge carriers in graphene. This allows the quantitative extraction of all electrical parameters (DC conductivity σDC, carrier density n, and carrier mobility μ) of large-scale graphene films placed on arbitrary substrates via THz-TDS. Particularly relevant are substrates with low relative permittivity (< 5) such as polymeric films, where notable renormalization effects are observed even at relatively large carrier densities (> 1012 cm-2, Fermi level > 0.1 eV). From an application point of view, the ability to rapidly and non-destructively quantify and map the electrical (σDC, n, μ) and electronic (νF*) properties of large-scale graphene on generic substrates is key to utilize this material in applications such as metrology, flexible electronics as well as to monitor graphene transfers using polymers as handling layers.
关键词： Graphene,THz-TDS,Fermi Velocity Renormalization,Mobility Mapping,Flexible Substrates
更新于2025-09-23 15:19:57