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Carrier transport improvement in ZnO/MgZnO multiple-quantum-well ultraviolet light-emitting diodes by energy band modification on MgZnO barriers
摘要： Ultraviolet (UV) light-emitting diodes (LEDs) based on zinc oxide (ZnO) materials have been the subject of many investigations because of their potential applications. In this study, ZnO/MgZnO multiple-quantum-well UV LEDs with graded-composition barriers were developed and numerically analyzed. The simulation results demonstrate that an optimized LED with a Mg composition graded from 24% to 2% in each triangular barrier exhibits the highest internal quantum efficiency (IQE) (88.0%) at 200 A/cm2, showing a 31.3% increase compared with the conventional LED with square barriers. This enhancement is attributed to the modified energy band structures that improve the symmetry in carrier transportation and increase the radiative recombination rate in each ZnO quantum well, thus enhancing the IQE of the device. Additionally, the different band-offset ratios of the MgZnO/ZnO and InGaN/GaN heterojunctions, which lead to the different carrier transport and electroluminescence properties of the ZnO- and GaN-based LEDs, were discussed here, providing researchers new insights into device design of ZnO-based LEDs.
关键词： Numerical simulation,Quantum barrier,Carrier transport,Zinc oxide,Light-emitting diode
更新于2025-09-12 10:27:22
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Impact of PbI <sub/>2</sub> Passivation and Grain Size Engineering in CH <sub/>3</sub> NH <sub/>3</sub> PbI <sub/>3</sub> Solar Absorbers as Revealed by Carrier‐Resolved Photo‐Hall Technique
摘要： With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley-Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI2 have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier-resolved photo-Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n-type MAPbI3 films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI2 added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier-related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI2 must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI3 optoelectronic properties as elucidated by the new CRPH approach.
关键词： photo-Hall characterization,defect passivation,charge carrier transport,perovskites,charge recombination
更新于2025-09-12 10:27:22
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Electrical Properties of Oxide-Confined Vertical-Cavity Surface-Emitting Lasers
摘要： We present a comprehensive description of electrical properties of vertical-cavity surface-emitting lasers (VCSELs) based on a drift-diffusion model applied to carrier transport in 3D multilayer semiconductor laser heterostructure with a p-n junction. We address the impact of interface grading in distributed Bragg reflectors (DBRs), modulation doping of the DBRs and surrounding layers of the quantum well (QW) as well as material-dependent carrier mobilities and recombination constants and are focused on oxide-confined GaAs/AlGaAs VCSELs. We evaluate both depletion and diffusion capacitance and show that both contributions to the capacitance as well as the differential series resistance critically depend on the injection current and chip design such that, in general, VCSEL cannot be properly modeled by an equivalent circuit approximation. Current profiles demonstrate significant increase of the current density at the edges of the oxide-confined aperture (current crowding) which could be suppressed by a proper design.
关键词： current crowding,differential resistance,oxide aperture,carrier transport,capacitance,modulation frequency bandwidth,vertical cavity surface-emitting laser
更新于2025-09-12 10:27:22
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Uniform Permutation of Quasi-2D Perovskites by Vacuum Poling for Efficient, High-Fill-Factor Solar Cells
摘要： It is widely accepted that vertically aligning quasi-2D perovskites can improve power conversion efficiency due to directional charge transport from small to large-n-value nanoplates. Here, we report a different strategy of uniformly arranging different-n-value 2D nanoplates (PEA2MAn-1PbnI3n+1) based on our vacuum poling method to enable superior isotropic carrier transport. Consequently, the high efficiency of 18.04% with open-circuit voltage of 1.223 V and champion fill-factor (FF) of 82.4% are demonstrated, presenting a new approach to develop advanced quasi-2D perovskite optoelectronic devices.
关键词： isotropic carrier transport,high-fill-factor,vacuum poling,solar cells,quasi-2D perovskites
更新于2025-09-11 14:15:04
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Enhanced Charge Carrier Transport in 2D Perovskites by Incorporating Single-Walled Carbon Nanotubes or Graphene
摘要： Two-dimensional (2D) organic-inorganic (hybrid) perovskites are considered promising candidates to replace conventional three-dimensional (3D) perovskites for solar cell applications as they have good resistance against moisture and UV light. However, the use of 2D perovskite is associated with a significant decrease in power efficiency resulting from their low photogenerated charge carrier density and poor charge transport. To improve power efficiency in 2D perovskites, highly crystalline films (near-single-crystal quality) of 2D perovskite needs to be synthesized where the alignment of the inorganic perovskite components is controlled to have vertical alignment with respect to the contacts to improve charge transport. In this work, we explored strategies to overcome this limitation, by integrating 2D perovskite with single-walled carbon nanotubes or graphene to enable more efficient extraction of charge carriers toward electric contacts. Longer carrier lifetimes were achieved after the incorporation of the carbon nanostructures in the films and at cell level, power efficiency increased by two-fold.
关键词： 2D perovskites,charge-carrier transport,solar cells,single-walled carbon nanotubes,graphene
更新于2025-09-11 14:15:04
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Enhanced carrier transport and bandgap reduction in sulfur-modified BiVO <sub/>4</sub> photoanodes
摘要： Recent progress on bismuth vanadate (BiVO4) has shown it to be among the highest performing metal oxide photoanode materials. However, further improvement, especially in the form of thin film photoelectrodes, is hampered by its poor charge carrier transport and its relatively wide bandgap. Here, sulfur incorporation is used to address these limitations. A maximum bandgap decrease of ~0.3 eV is obtained, which increases the theoretical maximum solar-to-hydrogen efficiency from 9 to 12%. Hard X-ray photoelectron spectroscopy (HAXPES) measurements as well as density functional theory (DFT) calculations show that the main reason for the bandgap decrease is an upward shift of the valence band maximum. Time-resolved microwave conductivity measurements reveal an ~3 times higher charge carrier mobility compared to unmodified BiVO4, resulting in a ~70% increase in the carrier diffusion length. This work demonstrates that sulfur doping can be a promising and practical method to improve the performance of wide-bandgap metal oxide photoelectrodes.
关键词： bismuth vanadate,photoelectrochemical performance,charge carrier transport,BiVO4,sulfur incorporation,bandgap reduction
更新于2025-09-11 14:15:04
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Double carrier transport in electron-doped region in black phosphorus FET
摘要： Double carrier transport has been observed in thin film black phosphorus (BP) field effect transistor devices in the highly electron-doped region. BP thin films with a typical thickness of 15 nm were encapsulated by hexagonal boron nitride thin films to avoid degradation by air exposure. Their Hall mobility reached 5300 cm2/V s and 5400 cm2/V s at 4.2 K in the hole- and electron-doped regions, respectively. The gate voltage dependence of conductivity exhibits an anomalous shoulder structure in the electron-doped region. In addition, at gate voltages above the shoulder, the magnetoresistance changes to positive, and there appears an additional slow Shubnikov-de Haas oscillation. These results strongly suggest the appearance of second carriers, which originate from the second subband with a localized band edge.
关键词： black phosphorus,Shubnikov-de Haas oscillation,double carrier transport,electron-doped region,field effect transistor
更新于2025-09-10 09:29:36
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Enhancement of transport properties in single ZnSe nanowire field-effect transistors
摘要： Wide-gap semiconductors are excellent candidates for next-generation optoelectronic devices, including tunable emitters and detectors. ZnSe nanowire-based devices show great promise in blue emission applications, since they can be easily and reproducibly fabricated. However, their utility is limited by deep level defect states that inhibit optoelectronic device performance. The primary objective of this work is to show how the performance of ZnSe nanowire devices improves when nanowires are subjected to a post-growth anneal treatment in a zinc-rich atmosphere. We use low temperature photoluminescence spectroscopy to determine the primary recombination mechanisms and associated defect states. We then characterize the electronic properties of ZnSe nanowire field effect transistors fabricated from both as-grown and Zn-annealed nanowires, and measure an order-of-magnitude improvement to the electrical conductivity and mobility after the annealing treatment. We show that annealing reduces the concentration of zinc vacancies, which are responsible for strong compensation and high amounts of scattering in the as-grown nanowires.
关键词： electrical resistivity,II–VI semiconductors,crystal defects,carrier transport,photoluminescence,carrier mobility,nanowires
更新于2025-09-09 09:28:46
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Optimizing nanoscale morphology and improving Carrier transport of PCDTBT-PCBM bulk heterojunction by cyclic carboxylate nucleating agents
摘要： In this work, four cyclic carboxylate commercial nucleating agents, bicyclo [2.2.1] heptane-2,3-dicarboxylic acid disodium salt (HPN-68L), sodium salt of hexahydrophthalic acid (HHPA-Na), sodium benzoate (Be-Na) and calcium salt of hexahydrophthalic acid (HPN-20E) were respectively added into poly[N-9’-heptadecanyl-2,7-carbazole-alt-5,5-(4’,7’-di-2-thienyl-2’,1’,3’ benzothiadi-azole)] (PCDTBT)-[6,6]-phenyl C61-butyric acid methyl ester (PCBM) blend. Atomic force microscopy (AFM) and UV-vis measurements indicate that the addition of carboxylic acid sodium salts can effectively optimize the morphology of active layer, decrease the phase domain size and increase the optical absorption intensity of PCDTBT-PCBM blends. The PCDTBT-PCBM-additive ternary devices were fabricated and found that adding carboxylic acid sodium salts can improve the hole mobility, balance the hole and electron mobility and finally increase the power conversion efficiency (PCE). Fixed the additive content as 5%, the modulation ability of the bicyclic dicarboxylic acid sodium salt HPN-68L is best, monocyclic dicarboxylic acid sodium salt HHPA-Na comes second, monocyclic carboxylic acid sodium salt Be-Na is worst. The addition of carboxylic acid calcium salt HPN-20E has no effects on the morphology and optical absorption intensity of the PCDTBT-PCBM blend, and the photoelectric properties of PCDTBT-PCBM-HPN-20E ternary device decreases in comparison with those of pristine PCDTBT-PCBM binary device. The modulation ability of cyclic carboxylate is related to its surface free energy and its location in the PCDTBT-PCBM blend. HPN-68L locates in the interfacial region between PCDTBT and PCBM, other cyclic carboxylates locates in the PCBM. Our finding suggests the addition of cyclic carboxylic acid sodium salts can be a facile approach to optimize the morphology and increase the electrical properties of organic materials for future development of organic photovoltaic devices.
关键词： PCDTBT-PCBM bulk heterojunction,carrier transport,organic photovoltaic devices,cyclic carboxylate nucleating agents,nanoscale morphology
更新于2025-09-09 09:28:46
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Radially resolved electronic structure and charge carrier transport in silicon nanowires
摘要： The electronic structure of silicon nanowires is studied using density functional theory. A radially resolved density of states is discussed for different nanowire diameters and crystal orientations. This approach allows the investigation of spatially varying electronic properties in the radial direction and extends previous studies, which are usually driven by a one-dimensional band structure analysis. We demonstrate strong differences in the electronic structure between the surface and the center of the nanowire, indicating that the carrier transport will mainly take place in the center. For increasing diameters, the density of states in the center approaches the bulk density of states. We find that bulk properties, such as the indirect nature of the band gap, become significant at a nanowire diameter of approximately 5 nm and beyond. Finally, the spatial characteristic of the current is visualized in terms of transmission pathways on the atomic scale. Electron transport is found to be more localized in the nanowire center than the hole transport. It also depends on the crystal orientation of the wire. For the growing demand of silicon nanowires, for example in the field of sensors or field-effect transistors, multiple conclusions can be drawn from the present work, which we discuss towards the end of the publication.
关键词： charge carrier transport,radially resolved density of states,silicon nanowires,density functional theory,electronic structure
更新于2025-09-09 09:28:46