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    Green Photonics Presentations

    Solid State Lighting and Displays
    (ordered chronologically by session start time)

    Visible luminescence in bulk and nanostructured ZnO
    Paper 8987-6

    Author(s):  Matthew R. Phillips, Univ. of Technology, Sydney (Australia), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 2: Photon-induced Phenomena
    Date and Time: 2/2/2014 10:15AM

    Cathodoluminescence studies have identified in bulk and nano-structured ZnO: green peaks centered at 2.30 eV GL1 (FWHM = 0.34 eV), 2.40 eV GL2 (FWHM = 0.50 eV) and 2.53 eV GL3 (FWHM = 0.45 eV); a yellow band at 2.12 eV (FWHM = 0.42 eV); and a red band at 1.76 eV (FWHM = 0.66 eV). Treatment in H plasma and forming gas has established that all bands except the yellow relate to intrinsic defects, with GL2, GL3 and RL involving acceptor-like centers. The YL can be attributed to a donor-acceptor pair with a deep Li acceptor.


    Spatial mapping of exciton lifetimes in single ZnO nanowires
    Paper 8987-11

    Author(s):  Frank Güell, Univ. de Barcelona (Spain), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 2: Photon-induced Phenomena
    Date and Time: 2/2/2014 11:55AM

    We investigate the spatial dependence of the exciton lifetimes in single ZnO nanowires. We have found that the free exciton and bound exciton lifetimes exhibit a maximum at the center of nanowires while they decrease by 30% towards the tips. This dependence is explained by considering the cavity-like properties of the nanowires in combination with the Purcell effect. We show that the lifetime of the bound-excitons scales with the localization energy to the power of 3/2 which validates the model of Rashba and Gurgenishvili at the nanoscale.


    Doping of Ga2O3 bulk crystals and NWs by ion implantation
    Paper 8987-16

    Author(s):  Katharina Lorenz, Univ. Técnica de Lisboa (Portugal), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 3: Doping and Band Structure Studies of Oxides
    Date and Time: 2/2/2014 2:50PM

    Ga2O3 is a promising host for optically active rare earth (RE) ions with sharp and temperature stable emission lines. Ga2O3 bulk crystals and nanowires have been implanted with Europium ions. Implantation damage consists of a mixture of defect clusters and extended defects such as dislocations. Amorphisation starts at the surface for fluences around 1x10^15 at/cm^2. Amorphous regions and defect clusters are efficiently removed during rapid thermal annealing at ~1100 ºC and RE ions are optically activated. However, extended defects still remain. Implantation at elevated temperature considerably reduces implantation damage and promotes the incorporation of Eu on substitutional lattice sites.


    Growth of bulk GaN crystal by Na flux method
    Paper 8986-2

    Author(s):  Yusuke Mori, Osaka Univ. (Japan), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 1: Growth I
    Date and Time: 2/3/2014 8:30AM

    We reported the recent advances in the growth of GaN crystals by Na flux method. In the case of the growth on a small GaN seed, Centimeter-sized buld GaN crystal could be obtained. No dislocations could by observed by the CL measurement from the GaN crystal grown on the small seed crystal. It is possible to coalesce GaN crystals grown from isolated small seed crystals without generation dislocations at boundary. The coalescence growth of GaN crystal from periodical arranged many small seed crystals seems to become a key technique for fabricating large-diameter high quality GaN crystals.


    New directions in GaN material research: thinner and smaller
    Paper 8986-11

    Author(s):  Jung Han, Yale Univ. (United States), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 3: Growth III
    Date and Time: 2/3/2014 1:15PM

    The past two decades have witnessed phenomenal progress in optoelectronic display and illumination devices enabled by AlGaInN (III-N). As the technology of conventional devices enters commercial maturity, innovation is called for continual advances in device applications. In this talk we will discuss the possibility of extending III-N devices in the directions of flexible and large-area applications. Our recent work in using electrochemical etching to achieve layer slicing will be presented with preliminary device demonstrations. We envision new possibilities in the manufacture of ultrathin and flexible GaN devices for photonic, electronic, and piezotronic applications. To circumvent the difficulty in the growth of GaN on silicon, we investigated the concept of evolutionary growth combining modern fabrication techniques with epitaxy to provide new freedoms in tackling this grand challenge. The result of preparing high quality, low dislocation GaN on amorphous SiO2 will be reported.


    Green- to red-emitting InGaN-based nanocolumn LEDs with regularly-arranged triangular lattice nanocolumn arrays
    Paper 8996-9

    Author(s):  Katsumi Kishino, Sophia Univ. (Japan), et al.
    Conference 8996: Quantum Dots and Nanostructures: Synthesis, Characterization, and Modeling XI Session 3: Nanowire Devices
    Date and Time: 2/3/2014 2:00PM

    Ti-mask selective area growth (SAG) was employed to fabricate triangular-lattice uniform arrays of GaN nanocolumn LED crystals. In this talk we describe fabrication and emission characteristics of InGaN-based green to red nanocolumn LEDs with the triangular-lattice nanocolumn arrays. Deposition of passivation layer on nanocolumn side walls contributed to elimination of unexpected current leakage paths. For red-emitting LEDs, the typical peak wavelength was 633 nm having the small blue shift of 5nm for increased injection current from 65 to 255 A/cm2. Green light (520-540nm) nanocolumn LEDs operated; the spectral FWHM was 35-50 nm and the typical turn-on voltage was 3.5 V.


    Defect-assisted exfoliation of GaN/InGaN flexible nanomembranes for optoelectronic applications
    Paper 8986-15

    Author(s):  Rami T. ElAfandy, King Abdullah Univ. of Science and Technology (Saudi Arabia), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 3: Growth III
    Date and Time: 2/3/2014 2:45PM

    We report on the defect assisted exfoliation of indium gallium nitride (InGaN) nanomembranes of different indium compositions using ultraviolet assisted wet etching. The surface defects are induced through inductively coupled plasma (ICP) system. Different powers and masks are used to engineer the nanomembranes dimensions. After exfoliation, the crystal quality is enhanced through rapid thermal annealing. High resolution transmission electron microscopy is employed to image the nanomembranes crystal quality. The exfoliated nanomembranes are then transferred to rigid substrates for subsequent overgrowth of high quality gallium nitride (GaN) using molecular beam epitaxy (MBE) or to flexible substrates for flexible electronics/photonics integrated devices.


    Effect of electrical field and atmosphere on the processing of nanocrystalline ZnO
    Paper 8987-41

    Author(s):  Benjamin Dargatz, Friedrich-Schiller-Univ. Jena (Germany), et al.
    Conference 8987: Oxide-based Materials and Devices V Session 8: Growth, Properties, and Applications of Nanostructures
    Date and Time: 2/3/2014 5:00PM

    The retention of nanocrystallinity in dense polycrystalline oxide materials is still a challenge, even with the application of stress-assisted methods like Spark Plasma Sintering. Interestingly, the combined effect of high heating rates and the presence of bound water seems to significantly promote densification of zinc oxide nanoparticles. Hence, dense nano-grained ZnO could be synthesized at a temperature of only 400 °C. In contrast, the sintering behavior of coarser powders is not affected by these conditions. The complementary roles of atmosphere, applied electrical field and heating rate on densification and coarsening mechanisms of zinc oxide will be highlighted in this talk.


    Quality of light of LED lighting: accurately rendering whites and colors
    Paper 9003-1

    Author(s):  Aurelien David, Soraa, Inc. (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 1: Solid State Lighting I
    Date and Time: 2/4/2014 10:30AM

    We present theoretical and experimental results on two important and overlooked aspects of LED's quality of light: - Whiteness rendering: many white objects contain fluorescing whitening agents which strongly improve whiteness perception when excited by the ultra-violet and violet light of natural light sources. To accurately render these objects, LED sources require a properly designed spectrum. - Color fidelity of real-world objects: the CRI calculation only considers a small number of color standards which can lead to inaccurate predictions of the color fidelity of a light source. By evaluating color fidelity over a large set of real-world objects, a better assessment of LED sources can be obtained.


    Principles of perfect and ultrathin anti-reflection with applications to transparent electrode
    Paper 8984-30

    Author(s):  Q-Han Park, Korea Univ. (Korea, Republic of), et al.
    Conference 8984: Ultrafast Phenomena and Nanophotonics XVIII Session 8: Nanophotonics
    Date and Time: 2/4/2014 11:30AM

    Perfect broad band anti-reflection (AR) through admittance matching has long been an important challenge in optics and electrical engineering. Beyond trial and error optimization, however, a systematic way to realize AR is still absent. Here, we report the discovery of an analytic solution to this long standing problem. We present a design rule for the ultra-thin AR coating which has been confirmed experimentally. This work opens a new design procedure for ultra-thin AR in optoelectronic devices, THz and microwave applications. Specifically, we explain applications of AR to transparent electrodes and present our recent achievement.


    Origin of non-radiative losses in thick InGaN/GaN QWs
    Paper 8986-26

    Author(s):  Felix Nippert, Technische Univ. Berlin (Germany), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 5: Material Characterization II
    Date and Time: 2/4/2014 11:45AM

    Efficient white light emitters require a drastic increase in efficacy of green LEDs. For this purpose we investigate InGaN quantum wells embedded in GaN, grown on c-sapphire by MOCVD. The QW thickness is varied between 2.2nm and 3.8nm, tuning the emission from 490nm and 540nm. Temperature-dependent photoluminescence shows a drastic decrease in room temperature efficiency for well thicknesses above 3nm, indicating a strong increase in non-radiative losses in these samples. We perform time- and spectrally- resolved photoluminescence to distinguish between effects of increased electron-hole-separation and defects as causes for this performance degradation.


    Phosphor-free InGaN/GaN/AlGaN core-shell dot-in-a-wire white light-emitting diodes
    Paper 9003-5

    Author(s):  Zetian Mi, McGill Univ. (Canada), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 2: Nanotechnologies for LEDs I
    Date and Time: 2/4/2014 1:30PM

    We have developed phosphor-free InGaN/GaN/AlGaN dot-in-a-wire core-shell white LEDs, which can break the carrier injection efficiency bottleneck of conventional nanowire white LEDs, leading to a dramatic enhancement of the output power. Additionally, such phosphor-free nanowire white LEDs can deliver an unprecedentedly high color rendering index (CRI) of ~92-98 in both the warm and cool white regions, with the color rendering capability approaching that of an ideal light source, i.e. a blackbody.


    2D- and 3D-patterned organic-inorganic hybrid systems for photonic applications
    Paper 8983-23

    Author(s):  Kwang-Sup Lee, Hannam Univ. (Korea, Republic of), et al.
    Conference 8983: Organic Photonic Materials and Devices XVI Session 6: Pattern Formation
    Date and Time: 2/4/2014 2:00PM

    Chemical protocols for incorporation of quantum dots into structures fabricated with two-photon lithography were recently developed in our group. To incorporate semiconductor quantum dots into 3D microstructures we have pursued a surface functionalization strategy. Cadmium selenide (CdSe) as well as core-shell CdS/ZnS, CdSe/ZnS and CdSe/ZnSe were functionalized with photosensitive monolayer to make them solution processable and photopatternable. The core-shell nanoparticles show more efficient flourecence and can be useful in display applications. These functionalized quantum dots can be easily dispersed in photopolymerizable resins to fabricate 3D structures.


    Direct verification of commonly-used rate-equation model in III-nitride material by detailed analysis of photoluminescence decay curves
    Paper 8986-30

    Author(s):  Hitoshi Manabe, Kanazawa Institute of Technology (Japan), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 6: Material Characterization III
    Date and Time: 2/4/2014 2:30PM

    The droop characteristics in nitride LEDs are usually analyzed by the following rate equation called “ABC model”; dn/dt=-An-Bn^2-Cn^3, which suggests the existence of Auger recombination. In this study, we checked the validity of the model directly by time-resolved photoluminescence (PL) measurements, and it is found that PL decay curves for GaN samples cannot be reproduced by the rate equation. Instead, the decay curves can be well-fitted by the stretched exponential functions usually used for amorphous semiconductors. These results indicate that the ABC model is not valid for GaN material, and suggest that GaN material has the aspect of disordered systems.


    Implementation of graphene electrodes in nanoparticle light-emitting devices
    Paper 9003-9

    Author(s):  Svenja Wolff, Univ. Duisburg-Essen (Germany), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 2: Nanotechnologies for LEDs I
    Date and Time: 2/4/2014 2:45PM

    Graphene is a very attractive candidate for “green” electrodes in future large-area light-emitting devices which are required to be cost-effective, robust and environmentally friendly. We demonstrate all-inorganic light emitting devices, implementing graphene layers as a promising substitute for ITO electrodes. Graphene monolayers were transferred onto glass substrates in an easy solution based approach at room temperature. Efficient luminescent quantum dots were used as a light emitting layer. After evaporation of a top electrode, a diode-like I-V characteristic was obtained. The obtained devices operate at a voltage at 4V and show large-area electroluminescence in the red spectral range.


    Efficiency droop improvement in InGaN/GaN light-emitting diodes by thinner quantum well with different location
    Paper 9003-15

    Author(s):  Sheng-Wen Wang, National Chiao Tung Univ. (Taiwan), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 3: High-Current LED Performance
    Date and Time: 2/4/2014 4:45PM

    We use thinner-quantum well to improve the droop behavior of light emitting diode. The thin quantum well will saturate easily, but this structure has more wave-function overlap than the thick well. This simulation result showed that decreasing the well thickness in specific position will not only improve the holes transport but also increase the quantum efficiency at high current density in the active region, and the efficiency droop behavior can be effectively suppressed. In this research, we designed the thin well structure and then put different numbers of the thinner-well on the active region and compared to the conventional LED.


    Identifying the cause of the efficiency droop in GaInN light-emitting diodes by correlating the onset of high injection with the onset of the efficiency droop
    Paper 9003-16

    Author(s):  David S. Meyaard, Rensselaer Polytechnic institute (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 3: High-Current LED Performance
    Date and Time: 2/4/2014 5:00PM

    An unequivocal correlation between the onset of high injection and the onset of the efficiency droop is demonstrated in GaInN light-emitting diodes over a wide range of temperatures. The diode voltage at the onset of high injection and the voltage at the onset of the efficiency droop are correlated by the equation V_High-injection onset + ΔV ≈ V_Droop onset. The excess voltage, ΔV, determined to be 0.3 V, drops partially over the p-type neutral region. The resulting electric field sweeps electrons out of the active region and results in substantial electron leakage despite high barriers that confine the carriers to the active region.


    Laser technology in automotive lighting
    Paper 8965-43

    Author(s):  Ceren Altingoz, Magneti Marelli Mako Elektrik Sanayi Ticaret A.S (Turkey), et al.
    Conference 8965: High-Power Diode Laser Technology and Applications XII Session PTue: Posters-Tuesday
    Date and Time: 2/4/2014 6:00PM

    Since Thomas Edison perfected the electronic light bulb over 130 years ago, our ability of creating artificial illumination has brightened up the coldness of night. From tungsten to halogen headlight bulbs, the recent phase apparent is HID which uses xenon gas to bring a near perfect white light to the road at about one-third of the power needed for a halogen setup. However, as HID headlamps are coming of age, a new challenge coming from full LED and OLED lighting systems. Standing at the edge of LEDs, future automotive lighting solutions could be found in LASERs.


    Nanorod-structured flip-chip GaN-based white light-emitting diodes
    Paper 9003-18

    Author(s):  Ching-Ting Lee, National Cheng Kung Univ. (Taiwan), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 4: Nanotechnologies for LEDs II
    Date and Time: 2/5/2014 9:00AM

    (Invited talk) By using the diffused ZnO nanorod reflector and the ZnO nanorod array antireflection layer, the light extraction and the light output power of the flip-chip white LEDs could be improved. The ZnO nanorod arrays grown on the top surface of de-vices could guide more blue light to efficiently excite phosphor and enhance phosphor conversion efficiency. The light out-put power and the phosphor conversion efficiency of the flip-chip white LEDs with diffused nanorod reflector and antireflection layer were enhanced 19.8 % and 4.3 % in comparison to the flip-chip white LEDs with flat reflector. This work was supported from NSC-101-2923-E-006-004-MY2.


    Plasmonic enhancement and losses in light-emitting quantum-well structures incorporating metallic gratings
    Paper 8980-34

    Author(s):  Toufik Sadi, Aalto Univ. (Finland), et al.
    Conference 8980: Physics and Simulation of Optoelectronic Devices XXII Session 9: Plasmonics
    Date and Time: 2/5/2014 10:30AM

    We analyze the physical role of surface plasmons in improving light extraction from GaN quantum-well (QW) light-emitting devices using first-principle theory based on Maxwell's equations and fluctuational electrodynamics. We explain experimental results demonstrating emission enhancement, light scattering and plasmonic coupling in structures incorporating a light-emitting QW and silver gratings. Results show considerable luminescence enhancement compared to ungrated structures but also significant optical losses introduced by the metallic grating. While the losses may be a significant obstacle for enhanced emission, careful engineering allows reducing such losses so that the benefits outweigh the increased losses.


    Highly-reliable Ag-based reflector for vertical-geometry GaN-based light-emitting diodes: Electrode design to improve the thermal stability
    Paper 9003-20

    Author(s):  Tae-Yeon Seong, Korea Univ. (Korea, Republic of), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 5: LED Fabrication
    Date and Time: 2/5/2014 10:30AM

    The most frequently used Ag reflector undergoes poor thermal instability. Thus, in this work, we show how to design Ag-based reflectors for the improvement of both the thermal and electrical properties. Compared to Ag only sample, Ag layers combined with interlayers, middle layers, capping layers and alloy layers exhibit much better optical reflectance and electrical properties. Blue LEDs with the 500 °C-annealed combined reflectors exhibit 25 – 33% higher output power (at 20 mA) than LEDs with the 500 °C-annealed Ag only reflectors. Based on SEM and X-ray results, mechanisms for the electrical and thermal improvement are described and discussed.


    New developments on high-efficiency infrared and InGaAlP light-emitting diodes at OSRAM OS
    Paper 9003-21

    Author(s):  Markus Broell, OSRAM Opto Semiconductors GmbH (Germany), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 5: LED Fabrication
    Date and Time: 2/5/2014 11:00AM

    Efficacies of light emitting diodes have been raised dramatically during the last decade leading to a broad range of new applications for automotive and consumer technologies. We present our latest results on developments of infrared and red light emitting diodes. Both chip types are based on the socalled Thinfilm technology. For infrared the chip efficiency has been raised by 25% with respect to former products and a record wall plug efficiency of more than 72% at a wavelength of 850nm has been reached. For red InGaAlP LEDs we could demonstrate a light output in excess of 200 lm/W and wall plug efficiencies above 60%.


    Miscibility and phase separation in LC semiconductor blends
    Paper 9004-7

    Author(s):  Yo Shimizu, National Institute of Advanced Industrial Science and Technology (Japan), et al.
    Conference 9004: Emerging Liquid Crystal Technologies IX Session 2: Lasing and Photonic Materials
    Date and Time: 2/5/2014 11:20AM

    LC miscibility is a macroscopic phenomenon. However, phase separation in the lower scale is sometimes considered for the emerged properties. It was found that mesogenic phthalocyanines with identical columnar mesophases show “miscibility” in the binary phase diagram. This binary system exhibits carrier mobility in the same order as those observed in the single component systems, though a slight difference in the HOMO and LUMO levels. This indicates miscibility of LCs is an interesting tool for the better light harvesting systems holding the efficiency in charge transport.


    III-nitride tunnel junctions for efficient solid state lighting
    Paper 8986-46

    Author(s):  Siddharth Rajan, The Ohio State Univ. (United States), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 10: LED I
    Date and Time: 2/5/2014 1:30PM

    We discuss the design and demonstration ultra-low resistance III-nitride tunnel junctions, and how tunnel junctions could solve the long-standing problem of efficiency droop in solid state lighting. We have used nanoscale band engineering based on polarization and mid-gap states to reduce tunneling resistance by four orders of magnitude. We will discuss experimental demonstration of highly efficient tunnel junctions (resistivity ~ 0.1 mOhm-cm^2) in PN junctions, p-contact free LEDs, and multiple junction structures. Finally we will show how tunneling based carrier regeneration in multiple active region cascade LEDs could help to enable low current, high voltage operation to overcome the efficiency droop problem.


    Surface-induced bistable switching liquid crystal mode and its electro-optic applications
    Paper 9004-9

    Author(s):  Hak-Rin Kim, Kyungpook National Univ. (Korea, Republic of), et al.
    Conference 9004: Emerging Liquid Crystal Technologies IX Session 3: Photoalignment, Photopatterning, and Phototuning
    Date and Time: 2/5/2014 1:50PM

    We present a bistable switching LC mode by using the topologically patterned LC anchoring surface. We analyze the effect of the surface topology and the elastic deformation energy of the LC bulk considering the LC chirality on the bistable LC anchoring and the bistable LC switching behaviors. By optimizing the LC chirality, we can obtain the symmetrically switchable bistable LC mode or the memory/dynamic dual switching LC mode. For 3D display applications requiring low power consumption, the LC parallax barrier and the LC lens operated by the memory mode will be presented.


    Enhanced light extraction and electrical properties of deep-ultraviolet light-emitting diodes by reflective contacts on selective-area-grown GaN
    Paper 9003-27

    Author(s):  Dong-Yeong Kim, Pohang Univ. of Science and Technology (Korea, Republic of), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 6: UV LEDs
    Date and Time: 2/5/2014 2:30PM

    Recently, AlGaN-based deep ultraviolet (DUV) light-emitting diodes (LEDs) have drawn great attention due to their potential applications such as purification of air and water, sterilization in food processing, UV curing, medical-, and defense-related light sources. However, widespread adoption of DUV LEDs instead of mercury-vapor lamps is obstructed by low external quantum efficiency (< 5% for 250nm) caused by low hole-injection efficiency and poor light extraction efficiency (LEE). LEE of DUV LEDs has not been enhanced as much as expected by conventional LEE-enhancing approaches used for visible LEDs, which originates from different intrinsic property between GaInN and AlGaN (Al > ~30%). Unlike GaInN visible LEDs, DUV light from a high Al-content AlGaN active region is transverse-magnetic (TM) polarized, that is, the electric field vector is parallel to the (0001) c-axis and shows strong side emission through m- or a-plane due to crystal-field split-off hole band being top most valence band. Therefore, a new LEE-enhancing approach addressing the unique intrinsic property of AlGaN DUV LEDs is strongly desired. In this study, we propose a new type of LEE-enhancing method for AlGaN-based DUV LEDs by utilizing its strong side emission. The Al0.55Ga0.45N/Al0.4Ga0.6N multiple quantum well LED structure with peak wavelength of ~280nm is grown by MOCVD on a c-plane sapphire substrate. The geometry of the DUV LED is designed to maximize the strong side emission from the MQW by fine-stripe mesa patterns and to reflect UV photons up to the free space by Al-coated selective-area-regrown GaN stripes, resulting in much enhanced LEE. In addition, the electrical properties of the DUV LED are improved substantially due to reduced specific contact resistivity as well as increased actual contact area on n-type AlGaN. The simultaneous improvements in optical and electrical properties of DUV LEDs by using the new approach will be discussed in detail with light propagating properties calculated by finite element analysis as well as an electrical conduction model.


    Design of a single projector multiview 3D display system
    Paper 8979-13

    Author(s):  Jason Geng, IEEE Intelligent Transportation Systems Society (United States), et al.
    Conference 8979: Emerging Digital Micromirror Device Based Systems and Applications VI Session 7: Advanced 3D Display
    Date and Time: 2/5/2014 3:30PM

    Multiview three-dimensional (3D) display is able to provide horizontal parallax to viewers with high-resolution and full-color images being presented to each view. Most multiview 3D display systems are designed and implemented using multiple projectors, each generating images for one view. Although this multi-projector design strategy is conceptually straightforward, implementation of such multi-projector design often leads to a very expensive system and complicated calibration procedures. Even for a multiview system with a moderate number of projectors (e.g., 32 or 64 projectors), the cost of a multi-projector 3D display system may become prohibitive due to the cost and complexity of integrating multiple projectors. In this article, we describe an optical design technique for a class of multiview 3D display systems that use only a single projector. The single projector is able to generate equivalent number of multiview images from multiple viewing directions, thus fulfilling the tasks of multiple projectors. An obvious advantage of the proposed SPM technique is the significant reduction of cost, size, and complexity, especially when the number of views is high. The SPM strategy also alleviates the time-consuming procedures for multi-projector calibration. The design method is flexible and scalable and can accommodate systems with different number of views.


    Internal quantum efficiency of InGaN/GaN LEDs with short period superlattice and two-colour quantum wells
    Paper 8986-79

    Author(s):  Ilya E. Titkov, Univ. of Dundee (United Kingdom), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    In this paper, internal quantum efficiency (IQE) of blue, deep green (560 nm) and monolithic white LEDs were measured by temperature dependant electro-luminescence (TDEL) and simulated with modified rate equation based on ABC model. InGaN/GaN short-period superlattices were fabricated using a method based on cycle conversion of surface In-GaN layer to GaN by application of growth interruptions in hydrogen atmosphere. Active regions of the investigated LEDs contain a combination of the SPSLs and 3 nm width InGaN layers. SPSL was about 24 nm thickness according to TEM. Temperature of growth of the InGaN layer was varied in the range of 810-900 C to change emission wavelength. Monolithic white LED structures with CCT in the range of 5000-11000 K contained one green InGaN QW and two blue QWs in active region separated by an SPSL-based barrier. External quantum efficiency exceeded 6% in maximum. IQE of blue and green quantum wells were analysed separately.


    Selective area growth for p-side down InGaN/GaN light-emitting diodes by metal-organic chemical vapor deposition
    Paper 8986-86

    Author(s):  Hsueh-Hsing Liu, National Central Univ. (Taiwan), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Piezoelectric polarization mismatch, which induces polarization sheet charge at InGaN/GaN interfaces and impacts carrier transport, is considered an important factor in the efficiency roll-off of these LEDs. P-side down LEDs, which have a reversed polarization field, is difficult to obtain a low resistance contact onto the dry-etched p-type area. In this work, we develop a regrowth process for the proposed p-down LEDs. By doing so, ohmic contacts with contact resistivity of 1.53×10-3 Ω-cm2. Preliminary measurements on the p-side down LEDs exhibit higher output power and less efficiency droop as compared to those of conventional p-side up ones.


    Compact remote water disinfection device using solar-powered deep-UV LEDs
    Paper 9003-51

    Author(s):  Brad Butterfield, Quantel USA (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Potable water that is disinfected and pure is an ongoing humanitarian need worldwide. This novel approach combines UV-C LEDs powered by a PV source to remotely purify non-turbid water in a compact portable design.


    Enhancement of light extraction efficiency with triangular-shaped GaN-based light-emitting diodes
    Paper 9003-55

    Author(s):  Ja-Yeon Kim, Korea Photonics Technology Institute (Korea, Republic of), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    We have investigated the quadrangular LED to various polygonal LEDs in an attempt to determine an optimum structure for improving the extraction and current injection efficiencies. To measure their electrical and optical properties, LEDs were packaged onto a TO-can after scribing with a diamond tip; the total radiant flux was then measured using an integrating sphere system. This study revealed similar I-V characteristics, while the polygonal LED showed an increase in the total radiant flux, compared to that of the quadrangular LED. Specifically, the triangular and hexagonal LED had good properties, resulting from an increase in its extraction and injection efficiency.


    Silver nanowire network for high-performance and transparent conducting electrode of GaN-based light-emitting diodes
    Paper 9003-60

    Author(s):  Ja-Yeon Kim, Korea Photonics Technology Institute (Korea, Republic of), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session PWed: Posters-Wednesday
    Date and Time: 2/5/2014 6:00PM

    Indium tin oxide (ITO) is widely used as a transparent conducting layer (TCL) in GaN based light emitting diodes. However, the transmittance of ITO decreases rapidly in the UV and near UV regions. Therefore, it is necessary to find a suitable material for TCLs. In this study, we demonstrate the characteristic of LED with Ag nanowire TCLs which has high transmittance in the UV region as well as high electrical conductivity. The electrical and optical performance of LED with silver nanowire TCL will be compared to those of conventional GaN LED with ITO.


    Microscopic models of non-radiative and high-current effects in LEDs: state of the art and future developments
    Paper 9003-36

    Author(s):  Enrico Bellotti, Boston Univ. (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 8: LED Efficiency Droop I: Joint Session with Conferences 8986 and 9003
    Date and Time: 2/6/2014 9:30AM

    We present an analysis of non-radiative and high current effects that are relevant to understand the performance of III-nitride LEDs. We discuss and compare models of radiative recombination, free carrier absorption, and non-radiative phenomena including direct and phonon-assisted Auger processes in InGaN/GaN quantum wells, and we assess the relative importance of these mechanisms on the internal quantum efficiency of green and blue LEDs. Finally, we demonstrate the necessity of a transport model able to capture the correct dynamics and energy distribution of carriers (such as Monte Carlo simulation) in order to elucidate which processes are responsible for droop.


    The efficiency droop in III-V semiconductor light-emitting diodes
    Paper 9003-38

    Author(s):  E. Fred Schubert, Rensselaer Polytechnic Institute (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 9: LED Efficiency Droop II: Joint Session with Conferences 8986 and 9003
    Date and Time: 2/6/2014 11:00AM

    Asymmetry of carrier-transport characteristics is an inherent property of III-V nitride semiconductor materials. Light-emitting diodes made of such materials have a propensity to easily enter the high-injection regime. In the high-injection regime, an electric field develops in the p-type region that extracts electrons from the active region (drift-leakage). It is shown that the onset of high injection precedes and is correlated to the onset of the efficiency droop, consistent with drift leakage being the cause of the efficiency droop.


    Low temperature studies of the efficiency droop in InGaN-based light-emitting diodes
    Paper 8986-62

    Author(s):  Jong-In Shim, Hanyang Univ. (Korea, Republic of), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 13: LED Efficiency Droop II: Joint Session with Conferences 8986 and 9003
    Date and Time: 2/6/2014 11:30AM

    We investigate the IQE droop behaviors from the cryogenic to room temperature in visible light-emitting diodes (LEDs). It is shown that all experimental IQE droops can be consistently explained by a model that posits the saturation of the radiative recombination rate at low current and subsequent increase in the nonradiative recombination rates at high current. Although a sudden increase of the nonradiative recombination rate is an apparent cause of the IQE droop, the saturation of the radiative recombination rate is the common trigger behind the IQE droop issue. We test the IQE droop model by introducing newly developed LED performance characterization techniques.


    Emerging applications of ferroelectric nanoparticles in display technologies
    Paper 9005-9

    Author(s):  Anatoliy V. Glushchenko, Univ. of Colorado at Colorado Springs (United States), et al.
    Conference 9005: Advances in Display Technologies IV Session 2: Emerging Technologies
    Date and Time: 2/6/2014 11:40AM

    Recent advances in the study of ferroelectric nanomaterials reveal the truly interdisciplinary nature of modern science and technologies. Physics, chemistry, material science, engineering, electronics, biology, medicine, and many other disciplines are coherently focused on different aspects of the same phenomenon: “ferroelectricity at nanoscale”. This interdisciplinary focus has resulted in the enormous broadening of the applications of ferroelectric nanoparticles during the last decade. This presented review is an attempt to describe and analyze the state of the field of applications of ferroelectric nanoparticles with a focus on materials and display technologies.


    Recent progress of deep UV LEDs and potential applications
    Paper 8986-63

    Author(s):  Kyoung Hoon Kim, LG Innotek (Korea, Republic of), et al.
    Conference 8986: Gallium Nitride Materials and Devices IX Session 14: LED II
    Date and Time: 2/6/2014 1:00PM

    We have been developing AlGaN based deep UV LEDs on c-plane sapphire substrate by specially designed high temperature (up to 1600 oC) MOCVDs. The high crystalline quality AlN, which is necessary to provide a template for deep UV LEDs structure, requires high growth temperature. It is believed that the efficiency of In free AlGaN quantum well structure is sensitive to the dislocation density resulted from the interface between AlGaN and sapphire substrate. Recently, thanks to the improvement of high quality AlN growth technology, we have achieved efficient and reliable deep UV LEDs with a mass producible yield. It is about to apply home appliance products. In this talk, we will present how we have improved the EQEs and reliabilities of deep UV LEDs using high quality AlN template. Also, we will discuss the potential applications of deep UV LEDs, mostly home appliances applications.


    Ammonothermal bulk GaN substrates for LEDs
    Paper 9003-39

    Author(s):  Mark P. D'Evelyn, Soraa, Inc. (United States), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 10: Novel Substrates for LEDs
    Date and Time: 2/6/2014 1:30PM

    GaN-on-GaN LEDs have demonstrated superior performance at very high current density. Soraa has developed a novel ammonothermal approach for growth of high quality bulk GaN crystals at reduced cost. Soraa’s approach utilizes internal heating to circumvent the material-property limitations of conventional ammonothermal reactors and provides capability for higher growth rates yet is less expensive. GaN crystals with diameters between 5 mm and 2" have been grown to thicknesses of 0.5-4 mm at rates well above 10 um/h. The crystals have excellent quality, with XRC FWHM values of 15-80 arc-sec and average dislocation densities below 1E5 cm-2.


    Spectral behavior and coherence length of GaN- and AlGaInP-based light-emitting diodes
    Paper 9003-45

    Author(s):  Reinhold Hetzel, Technische Univ. Graz (Austria), et al.
    Conference 9003: Light-Emitting Diodes: Materials, Devices, and Applications for Solid State Lighting XVIII Session 11: Solid State Lighting II
    Date and Time: 2/6/2014 4:15PM

    The coherence length of electromagnetic waves created by different light sources is a largely overlooked parameter. We studied the spectral emission of GaN- and AlGaInP-based Light-Emitting-Diodes (LEDs) driven by direct current and short current pulses in the temperature range from 4.2 to 390 Kelvin. The coherence length was measured via Fabry-Perot interference. Besides the distinct shifts of the emission wavelength accompanied by significant changes of the full width at half maximum, we found quite high values for the coherence length exceeding 0.15 millimeters for the blue emission and 0.4 millimeters for the red emission at room temperature, respectively.


    Important Dates

    Abstracts Due
    17 July 2017

    Author Notification
    25 September 2017

    Manuscripts Due
    See Individual Conferences


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    Journal of Photonics for Energy