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[IEEE 2019 8th International Conference on Modern Power Systems (MPS) - Cluj Napoca, Romania (2019.5.21-2019.5.23)] 2019 8th International Conference on Modern Power Systems (MPS) - Assessment of Photovoltaic Modules' Parameters Using the On-Site Measurements
摘要： Among various renewable energy sources, the photovoltaic technology is considered the proper technology for distributed power generation. The performance of electrical photovoltaic depends on their characteristics on various environmental conditions. The objective of this paper is to use the one-diode model together with on-site measurements, in order to evaluate the current-voltage and power-voltage curves and effects of irradiance and temperature on the performance the photovoltaic panel.
关键词： one-diode model,simulation,photovoltaic panel,data acquisition
更新于2025-09-11 14:15:04
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European Microscopy Congress 2016: Proceedings || SEM based electro-optical characterization of core-shell LEDs and simulation of imaging including CL and EBIC excitation inside ensembles
摘要： Three dimensional (3D) nano- and microstructures (NAMs) are attracting a lot of attention and are discussed regarding several applications, especially in optoelectronics and sensors. For example GaN based 3D light emitting diodes (LEDs) with a core-shell geometry are supposed to have substantial advantages over conventional planar LEDs: The active area along the sidewalls of hexagonal GaN pillars can considerably be increased by high aspect ratios - leading to a lower current density inside the InGaN quantum well (QW) at the same operation current per substrate area. [1] Thus related methods are requested for characterization of local electro-optical properties with a high spatial resolution on single structures as well as in ensembles. Usually, electron microscopy is employed to investigate the geometry and properties of such 3D-NAMs and for mapping of vertical features by an SEM a certain sample tilt (e.g. about 30°) is needed. Investigation of single 3D-LEDs by electron beam induced current (EBIC) using an SEM based manipulator setup proves the presence of a pn-junction and doping type of the core and shell, while cathodoluminescence (CL) gives an insight to the optical properties of the QW [2]. But in contrast to SEM on planar regions the interactions of the electron probe are significantly affected by the 3D geometry and the surrounding of the NAMs. In ensembles of 3D-NAMs a certain portion of incident electrons are scattered into neighbor structures and conventional SEM signals (SE, BSE, CL, X-ray emission) are partly shadowed. This interaction is affecting the SEM imaging contrast and the probed signal also includes contributions which are not related to the material properties at the electron beam spot. As such parasitic signals are generated quite close to the original region of the interaction most (global) SEM detectors cannot separate them from the original source. In particular scattering events occur in an enlarged volume of the sample (of the substrate and NAMs) leading to a reduced excitation density and parasitic effects, e.g. this causes a significant contribution of defect related yellow luminescence (YL) We present results of InGaN/GaN core-shell LEDs obtained with an FE-SEM which is equipped with SE, In-Beam SE, low-kV BSE, EBIC and monochromatic CL detection as well as a piezo controlled manipulator setup, see Figure 1. A modified parabolic collection mirror enables measuring luminescence from planar samples up to 4’’ in a tilted view up to 30°. For a quantitative interpretation of CL and EBIC measurement values and image contrasts, the physical modeling of SEM images and spatially resolved energy transfer by a probe spot is necessary. This is performed using the simulation program MCSEM [3]. It models the different stages of image formation and generates SEM images of complex NAM shapes using e.g. GaN as model material. Aspects of the simulation are the electron probe formation, a 3D model of the specimen structure, the interaction of electron probe and solid state by means of scattering trajectories, the emission of secondary electrons, and different types of electron detectors, see Figure 2 and Figure 3. An insight to CL and EBIC imaging is gained by evaluating the scattering energy deposited in a distinct volume inside the NAMs as an imaging signal - this is related to the generation rate of electron-hole pairs inside the respective volume of the semiconductor. Consent to the experiments this simulation reveals an edge contrast and shadowing of signals by the ensemble as well as scattering of primary electrons inside the ensemble of 3D-NAMs. A quantitative comparison is possible by the absorbed current (EBAC). Artefacts of the EBIC are also demonstrated by the simulation, in particular edge contrast by a reduced generation rate and parasitic signals by scattering from neighbor structures.
关键词： EBIC,cathodoluminescence,electron beam induced current,SEM simulation,core-shell LED
更新于2025-09-11 14:15:04
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Self-assembled monolayer for polymer-semiconductor interface with improved interfacial thermal management
摘要： Reliability and lifespan of highly miniaturized and integrated devices will be effectively improved if excessive accumulated heat can be quickly transported to heat sinks. In this study, both molecular dynamics (MD) simulations and experiments were performed to demonstrate that self-assembled monolayers (SAMs) have high potential in interfacial thermal management and can enhance thermal transport across polystyrene (PS) / silicon (Si) interface, modelling the common polymer/semiconductor interfaces in actual devices. The influence of packing density and alkyl-chain length of SAMs are investigated. Firstly, MD simulations show that the interfacial thermal transport efficiency of SAM is higher with high packing density. The interfacial thermal conductance (ITC) between PS and Si can be improved up to 127 ± 9 MW m-2 K-1, close to the ITC across metal and semiconductor interface. At moderate packing density, the SAMs with less than 8 carbon atoms in alkyl-chain show superior improvements over those with more carbons due to the assembled structure variation. Secondly, time-domain thermoreflectance technique was employed to characterize the ITCs of a bunch of Al/PS/SAM/Si samples. C6-SAM enhances the ITC by 5 folds, from 11 ± 1 MW m-2 K-1 to 56 ± 17 MW m-2 K-1. The interfacial thermal management efficiency will weaken when alkyl-chain exceeds 8 carbon atoms, which agrees with the ITC trend from MD simulations at moderate packing density. The relationship between SAM morphology and interfacial thermal management efficiency is also discussed in detail. This study demonstrates the feasibility of molecular level design for interfacial thermal management from both theoretical calculation and experiment, and may provide a new idea for improving the heat dissipation efficiency of micro devices.
关键词： polymer/semiconductor interface,time-domain thermoreflectance,molecular dynamics simulation,self-assembled monolayer,interfacial thermal management
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Fes, Morocco (25–27 March 2019)] 15th International Conference on Concentrator Photovoltaic Systems (CPV-15) - Numerical simulation of an ozone-based wet-chemical etching
摘要： In the PV-industry, wet-chemical baths are used for surface structuring, conditioning and cleaning. Besides cleaning the wafers, ozone-based wet-chemical cleaning processes show the ancillary effect of intendedly etching back the emitter and/or rounding of textured surfaces. To simulate and predict this rounding of micro-pyramids during the cleaning process, a two dimensional process simulation model was built. With the finite element method of COMSOL Multiphysics the diffusion and convection based mass transport of ozone along the pyramids is described. Important parameters for the evaluation, obtained from experimental results, are the etch rate and resulting roundness (R) of the micro-pyramids tips. A parametric study was carried out with the purpose of adjusting the model. The simulation represents the experimental data accurately, e.g. after 2 min exposure time R = 67 nm for the experimental and R = 66 nm for the simulation data.
关键词： PV-industry,numerical simulation,micro-pyramids,ozone-based wet-chemical etching,COMSOL Multiphysics
更新于2025-09-11 14:15:04
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Polarized Positron Beams via Intense Two-Color Laser Pulses
摘要： The generation of ultrarelativistic polarized positrons during the interaction of an ultrarelativistic electron beam with a counterpropagating two-color petawatt laser pulse is investigated theoretically. Our Monte Carlo simulation, based on a semiclassical model, incorporates photon emissions and pair productions, using spin-resolved quantum probabilities in the local constant field approximation, and describes the polarization of electrons and positrons for the pair production and photon emission processes, as well as the classical spin precession in between. The main reason for the polarization is shown to be the spin asymmetry of the pair production process in strong external fields, combined with the asymmetry of the two-color laser field. Employing a feasible scenario, we show that highly polarized positron beams, with a polarization degree of ζ ≈ 60%, can be produced in a femtosecond timescale, with a small angular divergence, ～74 mrad, and high density, ～1014 cm?3. The laser-driven polarized positron source raises hope for providing an alternative for high-energy physics studies.
关键词： polarized positron beams,ultrarelativistic electron beam,local constant field approximation,spin-resolved quantum probabilities,high-energy physics,Monte Carlo simulation,two-color laser pulses
更新于2025-09-11 14:15:04
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[IEEE 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Paris, France (2019.9.1-2019.9.6)] 2019 44th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz) - Open-Source Simulation Software for Quantum Cascade Lasers
摘要： We review the state of the art in open-source simulation and optimization tools for quantum cascade lasers (QCLs) and present the mbsolve project, which is a tool for QCL dynamics simulations.
关键词： open-source,quantum cascade lasers,dynamics simulations,mbsolve,simulation software
更新于2025-09-11 14:15:04
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Monte Carlo simulation of a transversely excited solar-pumped fiber laser
摘要： A Monte Carlo ray-tracing simulation was developed for a transversely excited solar-pumped fiber laser without focusing optics. To make this possible, the fiber is immersed in a liquid sensitizer and sandwiched between highly reflective mirrors. The top reflector is dichroic to transmit solar radiation but reflect fluorescence to confine photons that match the absorption band of the active fiber. Simulation was used to evaluate the validity of the concept and optimize device performance. For comparison with the calculations, preliminary experiments were conducted by illuminating a 30 cm aperture, laser module with a solar simulator. The observed gains were in good agreement with the calculations for various conditions, such as sensitizer concentration and mirror reflectivity. Finally, we show that the predicted output power reaches 29 mW when the fiber length is optimized, and it will be enhanced to 150 mW with 0.21% solar-to-laser efficiency under the assumption of a reabsorption-free sensitizer.
关键词： unconcentrated,dichroic mirror,Monte Carlo simulation,sensitizer,solar-pumped fiber laser,transversely excited
更新于2025-09-11 14:15:04
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A new ultra-scaled graphene nanoribbon junctionless tunneling field-effect transistor: proposal, quantum simulation, and analysis
摘要： In this paper, a new ultrascaled junctionless graphene nanoribbon tunnel field-effect transistor (JL GNRTFET) is proposed through a computational study. The quantum simulation approach is based on the resolution of the Schr?dinger equation using the mode space non-equilibrium Green’s function formalism coupled self-consistently with a Poisson equation in the ballistic limit. The proposed nanodevice is endowed with ungated region between the auxiliary and control gates as well as with a laterally graded channel doping in order to improve the switching performance of the ultrascaled junctionless GNRTFET. The performance assessment has included the IDS–VGS transfer characteristics, subthreshold swing, current ratio, intrinsic delay, and power-delay product. It has been found that the proposed ultrascaled junctionless GNR tunneling FET can provide improved switching performance than its conventional counterpart. The proposed strategy can be applied to improve similar ultrascaled junctionless tunneling field-effect transistors for the future digital electronics, where the high-performance and the aggressive downscaling should be in agreement.
关键词： Junctionless,Graphene nanoribbon (GNR),Tunneling field-effect transistor (TFET),Switching,Quantum simulation,Tunneling
更新于2025-09-11 14:15:04
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[IEEE 2019 Second Balkan Junior Conference on Lighting (Balkan Light Junior) - Plovdiv, Bulgaria (2019.9.19-2019.9.21)] 2019 Second Balkan Junior Conference on Lighting (Balkan Light Junior) - Investigating the Influence of Environmental and Design Parameters on the Thermal Regime of a LED Lamp
摘要： The increase of the LED’s temperature above a certain threshold decreases significantly their live expectancy. Therefore, it is important to investigate LEDs’ thermal regime during exploitation. The influence of the construction and the environment parameters on the thermal regime of LED lamp was investigated in this paper. The study was done with a specially developed software, based on a model, describing the thermal regime of LED lamps. Next, a methodology for the research has been developed and a simulation study was carried out. The results of this investigation are represented graphically.
关键词： simulation,model,LED lamp,investigation
更新于2025-09-11 14:15:04
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Parallel Simulation of Fully Coupled Electrothermal Processes in Large-Scale Phase-Change Memory Arrays
摘要： Numerical simulation of fully coupled electrothermal processes in phase-change memory (PCM) arrays is performed in this article. For realizing the ability in simulating the electrothermal responses of large-scale PCM arrays, an in-house parallel simulator based on domain decomposition method (DDM) and time-domain finite element method (FETD) is developed, with its performance evaluated in terms of accuracy and scalability. Then, thermal crosstalk in the PCM array is investigated using the developed simulator, and a diamond layer is introduced to suppress thermal crosstalk. Furthermore, the scaling effects of PCM arrays on their electrothermal performance are examined. A scheme for multibit PCM design is proposed, and the electrothermal characteristics of proposed 2-bit PCM cells and arrays are studied numerically.
关键词： phase-change memory (PCM),multibit PCM,parallel computing,time-domain finite element method (FETD),Electrothermal simulation,thermal crosstalk
更新于2025-09-11 14:15:04