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Special Issue "Light Emitting Diodes and Laser Diodes: Materials and Devices"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: 15 May 2018

Special Issue Editors

Guest Editor
Dr. Matteo Meneghini

Department of Information Engineering, University of Padua, Padua, Italy
Website | E-Mail
Interests: semiconductors; light-emitting diodes; laser diodes; solar cells; high mobility transistors
Guest Editor
Prof. Gaudenzio Meneghesso

Department of Information Engineering, University of Padova, Via Gradenigo 6/B, Padova 35131, Italy
Website | E-Mail
Interests: GaN based power devices; photovoltaics; RF-MEMS switches; organics devices; electrostatic discharge
Guest Editor
Prof. Enrico Zanoni

Department of Information Engineering, University of Padova, Via Gradenigo 6/B, Padova 35131, Italy
Website | E-Mail
Interests: microelectronics; electron devices; GaN and GaAs transistors; GaN LEDs; GaN lasers

Special Issue Information

Dear Colleagues,

The Special Issue on Light Emitting Diodes and Laser Diodes: Materials and Devices will offer an attractive forum to reflect the most recent theoretical and practical developments in the field of light-emitting diodes and laser diodes. The topics of this Special Issue include, but are not limited to, the following:

  • Growth and design

  • Polar, non-polar and semipolar materials

  • Light emitting device optimization

  • UV-emitting devices

  • Performance and reliability

  • Efficiency droop

  • Thermal droop

  • Nanostructures and optical devices

  • Nanowire LEDs

  • Substrates for light-emitting devices

  • Phosphors for solid-state lighting

  • Applications of LEDs and lasers

  • Defects in LEDs

  • Non-radiative processes

  • Simulation and optimization of LEDs

We would like to take this opportunity to invite you to submit your research findings to the Special Issue “Light Emitting Diodes and Laser Diodes: Materials and Devices”. Full research articles, short communications and comprehensive review papers are welcome.

Dr. Matteo Meneghini
Prof. Gaudenzio Meneghesso
Prof. Enrico Zanoni
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

 

Keywords

  • LED

  • Light-emitting diode

  • Laser diode

  • Characterization

  • Growth

  • Reliability

  • Defects

Published Papers (14 papers)

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Research

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Open AccessFeature PaperArticle GaN-Based Laser Wireless Power Transfer System
Materials 2018, 11(1), 153; doi:10.3390/ma11010153
Received: 25 November 2017 / Revised: 9 January 2018 / Accepted: 10 January 2018 / Published: 17 January 2018
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Abstract
The aim of this work is to present a potential application of gallium nitride-based optoelectronic devices. By using a laser diode and a photodetector, we designed and demonstrated a free-space compact and lightweight wireless power transfer system, whose efficiency is limited by the
[...] Read more.
The aim of this work is to present a potential application of gallium nitride-based optoelectronic devices. By using a laser diode and a photodetector, we designed and demonstrated a free-space compact and lightweight wireless power transfer system, whose efficiency is limited by the efficiency of the receiver. We analyzed the effect of the electrical load, temperature, partial absorption and optical excitation distribution on the efficiency, by identifying heating and band-filling as the most impactful processes. By comparing the final demonstrator with a commercial RF-based Qi system, we conclude that the efficiency is still low at close range, but is promising in medium to long range applications. Efficiency may not be a limiting factor, since this concept can enable entirely new possibilities and designs, especially relevant for space applications. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Mechanical, Thermodynamic and Electronic Properties of Wurtzite and Zinc-Blende GaN Crystals
Materials 2017, 10(12), 1419; doi:10.3390/ma10121419
Received: 30 October 2017 / Revised: 7 December 2017 / Accepted: 8 December 2017 / Published: 12 December 2017
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Abstract
For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s
[...] Read more.
For the limitation of experimental methods in crystal characterization, in this study, the mechanical, thermodynamic and electronic properties of wurtzite and zinc-blende GaN crystals were investigated by first-principles calculations based on density functional theory. Firstly, bulk moduli, shear moduli, elastic moduli and Poisson’s ratios of the two GaN polycrystals were calculated using Voigt and Hill approximations, and the results show wurtzite GaN has larger shear and elastic moduli and exhibits more obvious brittleness. Moreover, both wurtzite and zinc-blende GaN monocrystals present obvious mechanical anisotropic behavior. For wurtzite GaN monocrystal, the maximum and minimum elastic moduli are located at orientations [001] and <111>, respectively, while they are in the orientations <111> and <100> for zinc-blende GaN monocrystal, respectively. Compared to the elastic modulus, the shear moduli of the two GaN monocrystals have completely opposite direction dependences. However, different from elastic and shear moduli, the bulk moduli of the two monocrystals are nearly isotropic, especially for the zinc-blende GaN. Besides, in the wurtzite GaN, Poisson’s ratios at the planes containing [001] axis are anisotropic, and the maximum value is 0.31 which is located at the directions vertical to [001] axis. For zinc-blende GaN, Poisson’s ratios at planes (100) and (111) are isotropic, while the Poisson’s ratio at plane (110) exhibits dramatically anisotropic phenomenon. Additionally, the calculated Debye temperatures of wurtzite and zinc-blende GaN are 641.8 and 620.2 K, respectively. At 300 K, the calculated heat capacities of wurtzite and zinc-blende are 33.6 and 33.5 J mol−1 K−1, respectively. Finally, the band gap is located at the G point for the two crystals, and the band gaps of wurtzite and zinc-blende GaN are 3.62 eV and 3.06 eV, respectively. At the G point, the lowest energy of conduction band in the wurtzite GaN is larger, resulting in a wider band gap. Densities of states in the orbital hybridization between Ga and N atoms of wurtzite GaN are much higher, indicating more electrons participate in forming Ga-N ionic bonds in the wurtzite GaN. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Investigation of Saturation Effects in Ceramic Phosphors for Laser Lighting
Materials 2017, 10(12), 1407; doi:10.3390/ma10121407
Received: 31 October 2017 / Revised: 4 December 2017 / Accepted: 6 December 2017 / Published: 8 December 2017
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Abstract
We report observations of saturation effects in a Ce:LuAG and Eu-doped nitride ceramic phosphor for conversion of blue laser light for white light generation. The luminous flux from the phosphors material increases linearly with the input power until saturation effects limit the conversion.
[...] Read more.
We report observations of saturation effects in a Ce:LuAG and Eu-doped nitride ceramic phosphor for conversion of blue laser light for white light generation. The luminous flux from the phosphors material increases linearly with the input power until saturation effects limit the conversion. It is shown that the temperature of the phosphor layer influences the saturation power level and the conversion efficiency. It is also shown that the correlated color temperature (CCT), phosphor conversion efficiency and color rendering index (CRI) are dependent both on the incident power and spot size diameter of the illumination. A phosphor conversion efficiency up to 140.8 lm/W with CRI of 89.4 was achieved. The saturation in a ceramic phosphor, when illuminated by high intensity laser diodes, is estimated to play the main role in limiting the available luminance from laser-based lighting systems. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessFeature PaperArticle Effect of Electron Blocking Layer Doping and Composition on the Performance of 310 nm Light Emitting Diodes
Materials 2017, 10(12), 1396; doi:10.3390/ma10121396
Received: 10 November 2017 / Revised: 1 December 2017 / Accepted: 2 December 2017 / Published: 6 December 2017
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Abstract
The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence
[...] Read more.
The effects of composition and p-doping profile of the AlGaN:Mg electron blocking layer (EBL) in 310 nm ultraviolet B (UV-B) light emitting diodes (LEDs) have been investigated. The carrier injection and internal quantum efficiency of the LEDs were simulated and compared to electroluminescence measurements. The light output power depends strongly on the temporal biscyclopentadienylmagnesium (Cp 2 Mg) carrier gas flow profile during growth as well as on the aluminum profile of the AlGaN:Mg EBL. The highest emission power has been found for an EBL with the highest Cp 2 Mg carrier gas flow and a gradually decreasing aluminum content in direction to the p-side of the LED. This effect is attributed to an improved carrier injection and confinement that prevents electron leakage into the p-doped region of the LED with a simultaneously enhanced carrier injection into the active region. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Efficiency of True-Green Light Emitting Diodes: Non-Uniformity and Temperature Effects
Materials 2017, 10(11), 1323; doi:10.3390/ma10111323
Received: 17 August 2017 / Revised: 11 September 2017 / Accepted: 12 September 2017 / Published: 18 November 2017
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Abstract
External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have
[...] Read more.
External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have a multi-peak character, which could not be fitted by a simple ABC-model. This observation correlated with splitting of LED emission spectra into two peaks at certain currents. The characterization data are interpreted in terms of non-uniformity of the LED active region, which is tentatively attributed to extended defects like V-pits. We suggest a new approach to evaluation of temperature-dependent light extraction and internal quantum efficiencies taking into account the active region non-uniformity. As a result, the temperature dependence of light extraction and internal quantum efficiencies have been evaluated in the temperature range mentioned above and compared with those of blue LEDs. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessFeature PaperArticle A Practical Example of GaN-LED Failure Cause Analysis by Application of Combined Electron Microscopy Techniques
Materials 2017, 10(10), 1202; doi:10.3390/ma10101202
Received: 25 July 2017 / Revised: 8 October 2017 / Accepted: 17 October 2017 / Published: 19 October 2017
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Abstract
In this paper, we report a failure case of blue LEDs returned from a field application, and propose a practical way to identify the physical and structural reasons for the observed malfunction by a combination of different electron microscope techniques. Cathodoluminescence imaging and
[...] Read more.
In this paper, we report a failure case of blue LEDs returned from a field application, and propose a practical way to identify the physical and structural reasons for the observed malfunction by a combination of different electron microscope techniques. Cathodoluminescence imaging and electron beam induced current (EBIC) imaging are employed in order to visualize conductive paths through the device in conjunction with subsequent energy dispersive x-ray analysis (EDS), revealing a metal deposition along cracks in the semiconductor layer which short-circuit the device. We demonstrate that the electron beam induced current imaging, in conjunction with other microscopic and analytical techniques at µm scale, is a powerful combination for clearly resolving and visualizing the cause of failure in the GaN LED chip. However, this represents a case study of a real application, which may not have been generally observed in laboratory testing environment. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Photometric and Colorimetric Assessment of LED Chip Scale Packages by Using a Step-Stress Accelerated Degradation Test (SSADT) Method
Materials 2017, 10(10), 1181; doi:10.3390/ma10101181
Received: 17 September 2017 / Revised: 8 October 2017 / Accepted: 10 October 2017 / Published: 16 October 2017
Cited by 1 | PDF Full-text (3829 KB) | HTML Full-text | XML Full-text
Abstract
By solving the problem of very long test time on reliability qualification for Light-emitting Diode (LED) products, the accelerated degradation test with a thermal overstress at a proper range is regarded as a promising and effective approach. For a comprehensive survey of the
[...] Read more.
By solving the problem of very long test time on reliability qualification for Light-emitting Diode (LED) products, the accelerated degradation test with a thermal overstress at a proper range is regarded as a promising and effective approach. For a comprehensive survey of the application of step-stress accelerated degradation test (SSADT) in LEDs, the thermal, photometric, and colorimetric properties of two types of LED chip scale packages (CSPs), i.e., 4000 °K and 5000 °K samples each of which was driven by two different levels of currents (i.e., 120 mA and 350 mA, respectively), were investigated under an increasing temperature from 55 °C to 150 °C and a systemic study of driving current effect on the SSADT results were also reported in this paper. During SSADT, junction temperatures of the test samples have a positive relationship with their driving currents. However, the temperature-voltage curve, which represents the thermal resistance property of the test samples, does not show significant variance as long as the driving current is no more than the sample’s rated current. But when the test sample is tested under an overdrive current, its temperature-voltage curve is observed as obviously shifted to the left when compared to that before SSADT. Similar overdrive current affected the degradation scenario is also found in the attenuation of Spectral Power Distributions (SPDs) of the test samples. As used in the reliability qualification, SSADT provides explicit scenes on color shift and correlated color temperature (CCT) depreciation of the test samples, but not on lumen maintenance depreciation. It is also proved that the varying rates of the color shift and CCT depreciation failures can be effectively accelerated with an increase of the driving current, for instance, from 120 mA to 350 mA. For these reasons, SSADT is considered as a suitable accelerated test method for qualifying these two failure modes of LED CSPs. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Laser-Based Lighting: Experimental Analysis and Perspectives
Materials 2017, 10(10), 1166; doi:10.3390/ma10101166
Received: 2 August 2017 / Revised: 4 October 2017 / Accepted: 5 October 2017 / Published: 11 October 2017
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Abstract
This paper presents an extensive analysis of the operating principles, theoretical background, advantages and limitations of laser-based lighting systems. In the first part of the paper we discuss the main advantages and issues of laser-based lighting, and present a comparison with conventional LED-lighting
[...] Read more.
This paper presents an extensive analysis of the operating principles, theoretical background, advantages and limitations of laser-based lighting systems. In the first part of the paper we discuss the main advantages and issues of laser-based lighting, and present a comparison with conventional LED-lighting technology. In the second part of the paper, we present original experimental data on the stability and reliability of phosphor layers for laser lighting, based on high light-intensity and high-temperature degradation tests. In the third part of the paper (for the first time) we present a detailed comparison between three different solutions for laser lighting, based on (i) transmissive phosphor layers; (ii) a reflective/angled phosphor layer; and (iii) a parabolic reflector, by discussing the advantages and drawbacks of each approach. The results presented within this paper can be used as a guideline for the development of advanced lighting systems based on laser diodes. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Optical CAD Utilization for the Design and Testing of a LED Streetlamp
Materials 2017, 10(9), 985; doi:10.3390/ma10090985
Received: 7 August 2017 / Revised: 21 August 2017 / Accepted: 21 August 2017 / Published: 24 August 2017
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Abstract
The design and testing of LED lamps are vital steps toward broader use of LED lighting for outdoor illumination and traffic signalling. The characteristics of LED sources, in combination with the need to limit light pollution and power consumption, require a precise optical
[...] Read more.
The design and testing of LED lamps are vital steps toward broader use of LED lighting for outdoor illumination and traffic signalling. The characteristics of LED sources, in combination with the need to limit light pollution and power consumption, require a precise optical design. In particular, in every step of the process, it is important to closely compare theoretical or simulated results with measured data (obtained from a prototype). This work examines the various possibilities for using an optical CAD (Lambda Research TracePro) to design and check a LED lamp for outdoor use. This analysis includes the simulations and testing on a prototype as an example; data acquired by measurement are inserted into the same simulation software, making it easy to compare theoretical and actual results. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle The Degree of Temporal Synchronization of the Pulse Oscillations from a Gain-Switched Multimode Semiconductor Laser
Materials 2017, 10(8), 950; doi:10.3390/ma10080950
Received: 13 July 2017 / Revised: 9 August 2017 / Accepted: 12 August 2017 / Published: 15 August 2017
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Abstract
Langevin noise leads to inhibition of the temporal synchronization of the pulse oscillations from a gain-switched multimode semiconductor laser, resulting in the power reduction in optical beat detection. In this paper, the degree of the temporal synchronization of the pulse oscillations was examined
[...] Read more.
Langevin noise leads to inhibition of the temporal synchronization of the pulse oscillations from a gain-switched multimode semiconductor laser, resulting in the power reduction in optical beat detection. In this paper, the degree of the temporal synchronization of the pulse oscillations was examined by numerically estimating the output energy in THz time-domain spectroscopy (THz-TDS) using multimode semiconductor laser rate equations that include Langevin noise. The degree was estimated to be 95.5% from the ratio of the averaged THz-TDS output energy for the case where Langevin noise was included to that for when Langevin noise was excluded. Therefore, a gain-switched multimode semiconductor laser can be regarded as equivalent to optical pulses oscillating simultaneously in all modes in actual applications including optical beat detection. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Modeling the Non-Equilibrium Process of the Chemical Adsorption of Ammonia on GaN(0001) Reconstructed Surfaces Based on Steepest-Entropy-Ascent Quantum Thermodynamics
Materials 2017, 10(8), 948; doi:10.3390/ma10080948
Received: 21 July 2017 / Revised: 11 August 2017 / Accepted: 11 August 2017 / Published: 15 August 2017
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Abstract
Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on
[...] Read more.
Clearly understanding elementary growth processes that depend on surface reconstruction is essential to controlling vapor-phase epitaxy more precisely. In this study, ammonia chemical adsorption on GaN(0001) reconstructed surfaces under metalorganic vapor phase epitaxy (MOVPE) conditions (3Ga-H and Nad-H + Ga-H on a 2 × 2 unit cell) is investigated using steepest-entropy-ascent quantum thermodynamics (SEAQT). SEAQT is a thermodynamic-ensemble based, first-principles framework that can predict the behavior of non-equilibrium processes, even those far from equilibrium where the state evolution is a combination of reversible and irreversible dynamics. SEAQT is an ideal choice to handle this problem on a first-principles basis since the chemical adsorption process starts from a highly non-equilibrium state. A result of the analysis shows that the probability of adsorption on 3Ga-H is significantly higher than that on Nad-H + Ga-H. Additionally, the growth temperature dependence of these adsorption probabilities and the temperature increase due to the heat of reaction is determined. The non-equilibrium thermodynamic modeling applied can lead to better control of the MOVPE process through the selection of preferable reconstructed surfaces. The modeling also demonstrates the efficacy of DFT-SEAQT coupling for determining detailed non-equilibrium process characteristics with a much smaller computational burden than would be entailed with mechanics-based, microscopic-mesoscopic approaches. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessArticle Color Shift Failure Prediction for Phosphor-Converted White LEDs by Modeling Features of Spectral Power Distribution with a Nonlinear Filter Approach
Materials 2017, 10(7), 819; doi:10.3390/ma10070819
Received: 28 May 2017 / Revised: 27 June 2017 / Accepted: 7 July 2017 / Published: 18 July 2017
Cited by 2 | PDF Full-text (4858 KB) | HTML Full-text | XML Full-text
Abstract
With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to
[...] Read more.
With the expanding application of light-emitting diodes (LEDs), the color quality of white LEDs has attracted much attention in several color-sensitive application fields, such as museum lighting, healthcare lighting and displays. Reliability concerns for white LEDs are changing from the luminous efficiency to color quality. However, most of the current available research on the reliability of LEDs is still focused on luminous flux depreciation rather than color shift failure. The spectral power distribution (SPD), defined as the radiant power distribution emitted by a light source at a range of visible wavelength, contains the most fundamental luminescence mechanisms of a light source. SPD is used as the quantitative inference of an LED’s optical characteristics, including color coordinates that are widely used to represent the color shift process. Thus, to model the color shift failure of white LEDs during aging, this paper first extracts the features of an SPD, representing the characteristics of blue LED chips and phosphors, by multi-peak curve-fitting and modeling them with statistical functions. Then, because the shift processes of extracted features in aged LEDs are always nonlinear, a nonlinear state-space model is then developed to predict the color shift failure time within a self-adaptive particle filter framework. The results show that: (1) the failure mechanisms of LEDs can be identified by analyzing the extracted features of SPD with statistical curve-fitting and (2) the developed method can dynamically and accurately predict the color coordinates, correlated color temperatures (CCTs), and color rendering indexes (CRIs) of phosphor-converted (pc)-white LEDs, and also can estimate the residual color life. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Review

Jump to: Research

Open AccessReview Diffusion-Driven Charge Transport in Light Emitting Devices
Materials 2017, 10(12), 1421; doi:10.3390/ma10121421
Received: 31 October 2017 / Revised: 1 December 2017 / Accepted: 5 December 2017 / Published: 12 December 2017
PDF Full-text (3543 KB) | HTML Full-text | XML Full-text
Abstract
Almost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general
[...] Read more.
Almost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general lighting, the conventional DHJ design requires burying the active region (AR) inside a pn-junction. This has hindered the development of emitters utilizing nanostructured ARs located close to device surfaces such as nanowires or surface quantum wells. Modern DHJ III-N LEDs also exhibit resistive losses that arise from the DHJ device geometry. The recently introduced diffusion-driven charge transport (DDCT) emitter design offers a novel way to transport charge carriers to unconventionally placed ARs. In a DDCT device, the AR is located apart from the pn-junction and the charge carriers are injected into the AR by bipolar diffusion. This device design allows the integration of surface ARs to semiconductor LEDs and offers a promising method to reduce resistive losses in high power devices. In this work, we present a review of the recent progress in gallium nitride (GaN) based DDCT devices, and an outlook of potential DDCT has for opto- and microelectronics. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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Open AccessReview Strategies to Achieve High-Performance White Organic Light-Emitting Diodes
Materials 2017, 10(12), 1378; doi:10.3390/ma10121378
Received: 7 November 2017 / Revised: 25 November 2017 / Accepted: 27 November 2017 / Published: 1 December 2017
Cited by 2 | PDF Full-text (21705 KB) | HTML Full-text | XML Full-text
Abstract
As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin
[...] Read more.
As one of the most promising technologies for next-generation lighting and displays, white organic light-emitting diodes (WOLEDs) have received enormous worldwide interest due to their outstanding properties, including high efficiency, bright luminance, wide viewing angle, fast switching, lower power consumption, ultralight and ultrathin characteristics, and flexibility. In this invited review, the main parameters which are used to characterize the performance of WOLEDs are introduced. Subsequently, the state-of-the-art strategies to achieve high-performance WOLEDs in recent years are summarized. Specifically, the manipulation of charges and excitons distribution in the four types of WOLEDs (fluorescent WOLEDs, phosphorescent WOLEDs, thermally activated delayed fluorescent WOLEDs, and fluorescent/phosphorescent hybrid WOLEDs) are comprehensively highlighted. Moreover, doping-free WOLEDs are described. Finally, issues and ways to further enhance the performance of WOLEDs are briefly clarified. Full article
(This article belongs to the Special Issue Light Emitting Diodes and Laser Diodes: Materials and Devices)
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