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16.3: <i>Invited Paper:</i> New development in Red Light‐emitting Diodes (LEDs) using Eu‐doped GaN for Monolithic Micro‐LED Displays
摘要： There has been a strong demand to develop red light-emitting nitride semiconductors for the monolithic integration of the three primary colors (RGB) and the development of a high-resolution display. Such a display is a key device for 'a smart society', in which cyberspace (information processing) and physical space (things) interactively fuse. The ongoing search for an efficient red LED based on GaN is pivotal to those efforts. In blue and green LEDs, InxGa1-xN /GaN multi-quantum wells are used as an active layer. Emission wavelength is determined by In composition in the InGaN. A simple way to realize the red LED is to increase In composition to 0.5. However, lattice mismatch between InGaN and GaN becomes large in InGaN with high In composition, which leads to severe degradation of crystalline quality of InGaN quantum wells. Furthermore, lattice mismatch also induces huge piezoelectric field, resulting in poor radiative recombination due to quantum-confined Stark effects. We have worked on the development of semiconductors intra-center photonics. This novel photonics uses the intra-4f shell transitions of rare-earth ions doped in semiconductors. In 2009, we invented a narrow-band red LED using Eu-doped GaN (GaN:Eu). A main emission line with a half width of less than 1 nm is observed at 621 nm, which can be assigned to the 5D0–7F2 transition of Eu3+ ions. The wavelength is extremely stable against the ambient temperature. Due to optimization of the device processing, the output power of the LED has been increasing steadily to over 1 mW. Utilizing this red LED, small nitride-based monolithic high-resolution optical devices that comprise RGB GaN-based LEDs can be realized for micro-LED displays and/or lighting technology. One of limiting factors for more enhanced light output power is a relatively long radiative lifetime of the Eu emission in GaN:Eu (～300 μs). According to the Fermi’s golden rule, modifying the spontaneous emission rate of Eu ions can be achieved by increasing the photonic density of states at the frequency of spontaneous emission, as already demonstrated with a planar Fabry-Perot cavity. We have boosted the output power by actively manipulating radiative recombination probability at the atomic level of the Eu ions, which can be achieved through control of their photon fields in micro- and nano-cavities. In a GaN:Eu layer embedded in a microcavity consisting of an AlGaN/GaN distributed Bragg reflector (DBR) and a Ag reflecting mirror, a 21-fold increase of the Eu emission intensity was obtained under optical pumping at room temperature. Furthermore, in a preliminary LED with a microcavity consisting of ZrO2/SiO2 and AlInN/GaN DBRs, the output power was enhanced by 10 times. In the talk, current status of the LED and strategies for more improved output power will be presented.
关键词： Monolithic Micro-LED Displays,Eu-doped GaN,Intra-center photonics,Red Light-emitting Diodes,Nitride semiconductors
更新于2025-09-11 14:15:04
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P‐6.7: Investigation of Full‐Color Solutions for Micro‐LED Display
摘要： Micro-LED is considered as the next generation display technology and has got the attention of many research groups and companies in the world. It is a kind of display consists of microscopic LEDs integrated on driving circuit. And it has many advantages such as high brightness, low power consumption, quick response, wide viewing angle, self-emitting, long lifetime, good contrast, and due to its micro size, it has extremely high resolution which is really suitable for micro-display like VR and AR. However, there are still some problems need to be solved before it widely used in display market. In today's trend of pursuing colorization high resolution and high contrast ratio in display field, achieving high quality and high efficiency full- color display is one of the most important challenge for Micro- LED applications. In this paper, several feasible techniques of full-color Micro-LEDs are investigated.
关键词： quantum dot,micro-display,phosphor,Micro-LED,RGB,full-color display
更新于2025-09-11 14:15:04
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Copper‐Phosphine Supported Fe <sub/>3</sub> O <sub/>4</sub> @SiO <sub/>2</sub> as a Novel Reusable Nanocatalyst‐Catalyzed Tandem Reaction of Indole and Alcohols to Bis(indolyl)methanes under Blue LED Light
摘要： Nano Fe3O4@SiO2@TPP(cid:0) Cu as a novel heterogeneous nano-catalyst was prepared and authenticated by usual analytical and spectroscopic techniques. The prepared Fe3O4@SiO2@TPP(cid:0) Cu was applied to preparation of bis(indolyl) methane derivatives via a three-component reaction of aromatic alcohols with indoles under blue led lights. The advantages of this method are the selective oxidation of alcohols under mild conditions. The recycling studies revealed that catalyst could be easily recovered using an external magnet and reused for five times without significant loss of its catalytic activity.
关键词： Nano Fe3O4@SiO2@TPP(cid:0) Cu,Superparamagnetic nanocatalyst,Oxidation alcohols,Blue LED Light,Bis(indolyl)methanes
更新于2025-09-11 14:15:04
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New electrolytic capacitor-less LED driver based on model predictive control
摘要： The lifetime of light-emitting diode (LED) drivers is mainly affected by electrolytic capacitors. Therefore, it is necessary to eliminate electrolytic capacitors from LED drivers. Firstly, basic concept of LED driver without electrolytic capacitors is addressed in this paper. Then, a new electrolytic capacitor-less LED driver is proposed and its operation principles are analyzed in detail. In order to achieve better control effect, model predictive control (MPC) strategy is introduced in this topology. Following that, the mathematical model of the circuit which adopts MPC is derived. Finally, simulations and experiments on a 24 V, 3A laboratory prototype are carried out to verify the feasibility of the proposed topology and control strategy.
关键词： Flyback,Model predictive control,LED driver,Bidirectional cuk,Electrolytic capacitor-less
更新于2025-09-11 14:15:04
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Single Stage High Brightness LED Driver with Improved Power Quality
摘要： A single switch single stage 24watt power supply is presented to run a light emitting diode (LED) load. In this power supply, the Zeta converter is used to operate in continuous conduction mode (CCM) for maintaining desired output voltage. A proportional integral (PI) controller is also proposed in the feedback to make system stable. The need of proposed controller is justified from stability analysis of the system with the help of small signal average modeling. A simulation model of the proposed LED driver is also carried out in MATLAB/SIMLINK using sim-power toolbox environment for a universal ac input mains. The results confirm a constant current of 0.4amp at output with improved power quality parameters such as total harmonic distortion (THD) and power factor (PF). All outcomes lie under the limit of IEC 61000-3-2 standards that verifies the theoretical analysis.
关键词： Small Signal Average (SSA) Modeling,Continuous Conduction Mode (CCM),THD,LED Driver,Power Factor (PF),Stability,Zeta dc-dc Converter
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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Confinement Effects and Charge Dynamics in Zn <sub/>3</sub> N <sub/>2</sub> Colloidal Quantum Dots: Implications for QD-LED displays.
摘要： Zinc nitride (Zn3N2) colloidal quantum dots are composed of non-toxic, low-cost and earth-abundant elements. The effects of quantum confinement on the optical properties and charge dynamics of these dots are studied using steady state optical characterization and ultrafast fluence-dependent transient absorption. The absorption and emission energies are observed to be size tunable, with the optical band gap increasing from 1.5 eV to 3.2 eV as the dot diameter decreased from 8.9 nm to 2.7 nm. Size dependent absorption cross sections (?? = 1.22 ± 0.02 ? 10-15 cm2 to 2.04 ± 0.03 ? 10-15 cm2), single exciton lifetimes (0.36 ± 0.02 ns to 0.65 ± 0.03 ns), as well as Auger recombination lifetimes of biexcitons (3.2 ± 0.4 ps to 5.0 ± 0.1 ps) and trions (20.8 ± 1.8 ps to 46.3 ± 1.3 ps) are also measured. The degeneracy of the conduction band minimum (?? = 2) is determined from the analysis of the transient absorption spectra at different excitation fluences. The performance of Zn3N2 colloidal quantum dots thus broadly matches that of established visible light emitting quantum dots based on toxic or rare elements, making them a viable alternative for QD-LED displays.
关键词： charge dynamics,zinc nitride,quantum confinement,QD-LED,quantum dots
更新于2025-09-11 14:15:04
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Cardiac pacing using transmural multi-LED probes in channelrhodopsin-expressing mouse hearts
摘要： Optogenetics enables cell-type specific monitoring and actuation via light-activated proteins. In cardiac research, expressing light-activated depolarising ion channels in cardiomyocytes allows optical pacing and defibrillation. Previous studies largely relied on epicardial illumination. Light penetration through the myocardium is problematic when moving to larger animals and humans. To overcome this limitation, we assessed the utility of an implantable multi light-emitting diode (LED) optical probe (IMLOP) for intramural pacing of mouse hearts expressing cardiac-specific channelrhodopsin-2 (ChR2). Implantable probes should cause minimal damage. Here we demonstrated that IMLOP insertion needs approximately 20 mN of force, limiting possible damage from excessive loads applied during implantation. Histological sections confirmed the confined nature of tissue damage during acute use. The temperature change of the surrounding tissue was below 1 K during LED operation, rendering the probe safe for use in situ. This was confirmed in control experiments where no effect on cardiac action potential (AP) conduction was observed even when using stimulation parameters twenty-fold greater than required for pacing. In situ experiments on ChR2-expressing mouse hearts demonstrated that optical stimulation is possible with light intensities as low as 700 μW/mm2; although stable pacing requires higher intensities. When pacing with a single LED, rheobase and chronaxie values were 13.3 ± 0.9 mW/mm2 and 3 ± 0.6 ms, respectively. When doubling the stimulated volume the rheobase decreased significantly (6.5 ± 0.9 mW/mm2). We have demonstrated IMLOP-based intramural optical pacing of the heart. Probes cause locally constrained tissue damage in the acute setting and require low light intensities for pacing. Further development is necessary to assess effects of chronic implantation.
关键词： Channelrhodopsin-2,Implantable multi-LED optical probe,Cardiac pacing,Intramural pacing,Optogenetics
更新于2025-09-11 14:15:04
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[IEEE 2019 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) - Auckland, New Zealand (2019.5.20-2019.5.23)] 2019 IEEE International Instrumentation and Measurement Technology Conference (I2MTC) - Experimental characterization of off-the-shelf LEDs as photodetectors for waking up microcontrollers
摘要： The use of LEDs as photodetectors has been subject of study for a long time. However, LEDs manufacturers do not provide information about the response of LEDs to the light. It is essential for the designers of electronic devices to know what the behavior of LEDs is so as to develop new applications in this area. In this work, we propose the use of commercially off-the-shelf LEDs, illuminated by the flashlight of a smartphone, as a contactless wake-up system for microcontrollers that are in a sleep mode. In particular, the generated LED voltage is proposed as the wake-up signal. So, in order to choose the most suitable LED and depending of the main interfering light, the current- voltage (I-V) characterization of different kind of LEDs is performed for two scenarios: outdoors and indoors. It is demonstrated that placing a resistor in parallel with the LEDs allows a better discrimination between the LED voltage coming from the flashlight and that from the interfering lights. Results show that red and blue LEDs are more appropriate for outdoor and indoor applications, respectively.
关键词： wake-up system,LED,photodetector,microcontroller
更新于2025-09-11 14:15:04
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Buck-Boost-Buck Type Single-Switch Multi-String Resonant LED Driver with High Power Factor and Passive Current Balancing
摘要： An integrated buck-boost-buck type single-switch multi-string resonant LED driver is proposed and analyzed. It combines buck-boost and buck converters to achieve passive current balancing and power factor correction (PFC). With this circuit configuration, the proposed LED driver employs only one low-side connection active switch, resulting in a very simple control requirement involving one closed-loop controller for regulating one output current. Other output currents can be balanced automatically by resonant capacitor and storage capacitors, making the control strategy economical. In addition, high efficiency is achieved due to single-stage power conversion. Taking three-string LED driver as an example, the proposed buck-boost-buck type single-switch LED driver is studied in terms of operating principle, current balancing principle, power factor (PF) analysis, voltage gain and key circuit parameter design. Finally, an 84W high PF three-string LED driver prototype with 94.3% peak efficiency is built to verify the analytical results.
关键词： passive current balancing,multi-string,single switch,power factor correction (PFC),Buck-boost-buck,LED driver
更新于2025-09-11 14:15:04