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Coaxial GaAs/(In,Ga)As Dot-in-a-Well Nanowire Heterostructures for Electrically Driven Infrared Light Generation on Si in the Telecommunication O Band
摘要： Core-shell GaAs-based nanowires monolithically integrated on Si constitute a promising class of nanostructures that could enable light emitters for fast inter- and intrachip optical connections. We introduce and fabricate a coaxial GaAs/(In,Ga)As dot-in-a-well nanowire heterostructure to reach spontaneous emission in the Si transparent region, which is crucial for applications in Si photonics. Specifically, we achieve room temperature emission at 1.27 μm in the telecommunication O band. The presence of quantum dots in the heterostructure is evidenced by a structural analysis based on scanning transmission electron microscopy. The spontaneous emission of these nanowire structures is investigated by cathodoluminescence and photoluminescence spectroscopy. Thermal redistribution of charge carriers to larger quantum dots explains the long wavelength emission achieved at room temperature. Finally, in order to demonstrate the feasibility of the presented nanowire heterostructures as electrically driven light emitters monolithically integrated on Si, a light emitting diode is fabricated exhibiting room-temperature electroluminescence at 1.26 μm.
关键词： Electroluminescence,Si substrates,Dot-in-a-well,Light emitting diode,Nanowire heterostructures
更新于2025-09-12 10:27:22
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Acetonitrile based single step slot-die compatible perovskite ink for flexible photovoltaics
摘要： The demonstration of photovoltaic devices with high power conversion efficiencies using low cost perovskite materials hints at the possibility of dramatically lowering the cost of solar energy. Key to further exploiting the potential of these materials is developing rapid processing techniques that can be used to deliver lower cost high throughput manufacture. This work details the development of low-viscosity rapid drying perovskite formulations designed to give high quality solar films when slot-die coated on flexible roll-to-roll compatible substrates. A single step slot-die compatible perovskite ink based on an acetonitrile/methylamine solvent system utilizing a chloride additive is developed, resulting in large area perovskite films from slot-die coating under ambient conditions. The drying conditions for the perovskite film are optimized and fast (<10 min), low temperature (<120 °C) drying of slot-die coated films on flexible substrates are demonstrated and result in high performance devices.
关键词： acetonitrile,chloride additive,flexible substrates,methylamine,photovoltaics,perovskite,slot-die coating
更新于2025-09-12 10:27:22
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Growth of InGaN films on hardness-controlled bulk GaN substrates
摘要： We carried out an evaluation of the crystalline quality of bulk GaN substrates and the properties of InGaN ?lms grown on them. The Urbach energy estimated by photothermal de?ection spectroscopy and the tail states near the valence band maximum determined by hard x-ray photoemission spectroscopy were larger for hardness-controlled bulk GaN (hard GaN) than those for conventional bulk GaN (conventional GaN). However, InGaN on hard GaN grows in a step-?ow-like mode, while InGaN grown on conventional GaN exhibits spiral-like growth. The photoluminescence decay at room temperature for InGaN grown on the hard GaN was 470 ps, compared with 50 ps for that grown on the conventional GaN. This can be attributed to the suppression of spiral-like growth due to the resistance to deformation of the hard GaN. These results indicate that substrate hardness is one of the most important factors for III–V nitride growth on the bulk GaN substrate.
关键词： hard x-ray photoemission spectroscopy,photoluminescence,bulk GaN substrates,InGaN films,photothermal de?ection spectroscopy,crystalline quality
更新于2025-09-11 14:15:04
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Highly Foldable and Efficient Paper-Based Perovskite Solar Cells
摘要： Foldable paper-based solar cells are attractive power sources for wearable and portable applications. Currently, low power conversion efficiency (PCE) and degradation under different folding conditions restrict practical applications of paper-based solar cells. Herein are constructed solar cells on cellophane paper using oxide/ultrathin Ag/oxide (OMO) and perovskite as electrodes and absorbers, respectively. The perovskite solar cell (PSC) on cellophane exhibits a PCE of 13.19%, the highest among all the paper-based solar cells. More importantly, beneficial from ultrathin cellophane substrates combined with foldable OMO electrodes, PSCs on paper exhibit 50 single folding and 10 dual folding stability: they preserve 85.3 and 84.1% of the initial PCE after (cid:1)180(cid:3) and t180(cid:3) single folding for 50 cycles, respectively; and they remain 67.2 and 55.3% of the initial PCE after 10 inner and outer dual folding cycles, respectively. Furthermore, the solar cells after dual folding show serious cracks and delamination, leading to faster degradation than single folding. The highly efficient, foldable, and lightweight PSCs on cellophane are promising for future self-powered paper-based electronic applications.
关键词： foldable,perovskite solar cells,cellophane paper substrates,high-efficiency
更新于2025-09-11 14:15:04
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Photoluminescence properties as a function of growth mechanism for GaSb/GaAs quantum dots grown on Ge substrates
摘要： In this work, we use photoluminescence (PL) spectroscopy to investigate how self-assembled GaSb/GaAs quantum dots (QDs) depend on their growth mechanism. Carrier transfer (i.e., carrier recombination in QDs and escape through the barrier layer) is investigated as a function of excitation-power- and temperature-dependent PL measurements. A drastic blueshift of the QD peak energy from 1.23 to 1.30 eV and a further shift to 1.33 eV reveal the influence of the GaSb growth rate and the growth temperature on the optical properties of these QDs. The thermal activation energy is extracted from the temperature-dependent PL by fitting the integrated PL intensity of the QD peaks to the Arrhenius relation. The QDs grown at the growth rate of 0.1 monolayers/s at 450 °C have higher thermal activation energy (109 meV) than those grown at a lower growth rate and higher QD growth temperature. The observed PL characteristics are discussed in terms of QD size, uniformity of QDs, and material intermixing occurring during QD growth on the buffer layer and capping layer.
关键词： Ge substrates,quantum dots,photoluminescence,GaSb/GaAs,growth mechanism
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Atlanta, GA, USA (2019.7.7-2019.7.12)] 2019 IEEE International Symposium on Antennas and Propagation and USNC-URSI Radio Science Meeting - Performance Comparison of Silicon Substrates for IC-Waveguide Integration based on a Contactless Transition at mm-Wave frequencies
摘要： This paper presents a comparison between different silicon (Si) substrates used in Si-based IC technologies at E-Band (71–86 GHz). A unique low-loss and compact contactless transition from a silicon IC (p-doped substrate) to a metal waveguide is used. The proposed transition incorporates a spatial power combiner to enable direct electromagnetic coupling from an array of patches on the IC to a metal waveguide. This design enables a high-power transition from an IC to a waveguide and/or antenna at millimeter-wave (mm-wave) frequencies, where a galvanic contact between the two parts is avoided.
关键词： IC-waveguide integration,millimeter-wave frequencies,contactless transition,silicon substrates,spatial power combiner
更新于2025-09-11 14:15:04
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Reduction in crystalline quality anisotropy for non-polar a-plane GaN directly grown on titanium patterned sapphire substrate
摘要： Nonpolar a-plane GaN films were directly grown on titanium patterned sapphire substrates (Ti-PSS) by metalorganic chemical vapor deposition (MOCVD). It is demonstrated that the GaN film grown on Ti-PSS has superior surface quality and less surface pits than that on flat sapphire substrate. More importantly, the anisotropic behavior of the X-ray rocking curve-full width at half maximum values for the on-axis reflections were significantly improved. It is found that, the increased mosaic block size along m-direction could be the main reason for the reduction in the crystalline quality anisotropy. This work provides a simple and effective method to improve the crystal quality of non-polar GaN films.
关键词： X-ray rocking curve,crystalline quality anisotropy,MOCVD,titanium patterned sapphire substrates,Nonpolar a-plane GaN
更新于2025-09-10 09:29:36
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Uniform Insulating Properties of Low-Temperature Curable Gate Dielectric for Organic Thin-Film Transistor Arrays on Plastic Substrate
摘要： Achieving a high-resolution display on a plastic substrate requires a to ensure dimensional stability during fabrication process, including the deposition of gate dielectrics. Evaluation platform to confirm the uniform insulating properties of organic dielectric material prior to actual application to organic thin-film transistor (OTFT) arrays was proposed. This test method enabled verification of the suitability of the low-temperature curable dielectric and chemical resistance during fabrication process. A cross-linked poly(hydroxy imide) (PHI) that can be cured at a low temperature of 130°C exhibited stable insulating properties in a large area that sudden breakdown was not observed in an electric field up to 4 MV/cm. Thiophene-thiazole-based copolymer semiconductor was used as an active layer and inkjet-printed. In all the processes, the temperature of the substrate was kept below 130°C, and 4.8-inch electrophoretic display panels on a polyethylene naphthalate (PEN) substrate with a resolution of 98 dpi was demonstrated.
关键词： Organic thin-film transistors,Organic gate dielectric,Plastic substrates,Low-temperature process,Polymer semiconductor,Flexible displays,Inkjet printing
更新于2025-09-10 09:29:36
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Two-dimensional Monte Carlo simulations of coarse-grained poly(3-hexylthiophene) (P3HT) adsorbed on striped substrates
摘要： We investigate the structural phases of single poly(3-hexylthiophene) (P3HT) polymers that are adsorbed on a two-dimensional substrate with a striped pattern. We use a coarse-grained representation of the polymer and sophisticated Monte Carlo techniques such as a parallelized replica exchange scheme and local as well as non-local updates to the polymer’s configuration. From peaks in the canonically derived observables, it is possible to obtain structural phase diagrams for varying substrate parameters. We find that the shape of the stripe pattern has a substantial effect on the obtained configurations of the polymer and can be tailored to promote either more stretched out or more compact configurations. In the compact phases, we observe different structural motifs, such as hairpins, double-hairpins, and interlocking “zipper” states.
关键词： coarse-grained,striped substrates,Monte Carlo simulations,poly(3-hexylthiophene),P3HT,structural phases
更新于2025-09-10 09:29:36
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Fabrication of Thin Functional Films by Solution Aerosol Thermolysis (SAT)
摘要： The technique of air-pressurized solution spray pyrolysis was used to fabricate thin films of La0.75Sr0.25MnO3 (LSM) and CuO-CeO2 on dense YSZ substrates. These films are widely used in several applications such as high temperature ceramic electrochemical cells, membranes and sensors. The technique was tailored to produce films with differing morphologies and thicknesses in terms of applied substrate deposition temperatures. The droplet drying and decomposition kinetics is discussed as a function of substrate temperature, given the other processing parameters (i.e. nozzle to substrate distance, solution flow rate, air pressure/air flow rate and deposition time) constant. A graph-map is drawn containing morphology and quality of fabricated films in terms of substrate temperatures and concentration levels for this particular set of precursor salts in aqueous solutions. Within the deposition temperature range examined, film thicknesses were found to decrease with increasing substrate temperature along with a concomitant change in quality from irregular texture to smoother and of more uniform thickness. A maximum deposition temperature of about 280?C was identified for 0.025M concentration for both types of films which correlates quite well with the Leidenfrost point measured in the literature for solvents with boiling point less than 150?C.
关键词： YSZ substrates,spray pyrolysis,thin films,LSM,CuO-CeO2,solution aerosol thermolysis
更新于2025-09-10 09:29:36