Author
Siddha Pimputkar
Other affiliations: University of California, Lehigh University, Lawrence Livermore National Laboratory
Bio: Siddha Pimputkar is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Nitride & Crystal. The author has an hindex of 14, co-authored 44 publications receiving 2506 citations. Previous affiliations of Siddha Pimputkar include University of California & Lehigh University.
Topics: Nitride, Crystal, Seed crystal, Gallium nitride, Crystal growth
Papers
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TL;DR: More than one-fifth of US electricity is used to power artificial lighting as discussed by the authors and light-emitting diodes based on group III/nitride semiconductors are bringing about a revolution in energy-efficient lighting.
Abstract: More than one-fifth of US electricity is used to power artificial lighting. Light-emitting diodes based on group III/nitride semiconductors are bringing about a revolution in energy-efficient lighting.
1,779 citations
TL;DR: In this article, a review of the unique polarization anisotropy in gallium nitride (GaN) is included for the different crystal orientations, highlighting high power violet and blue emitters, and the effects of indium incorporation and well width.
346 citations
TL;DR: In this article, a new scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized, focusing on two classes of high-light-yield materials: europium-doped alkaline earth halides and ceriumdoped garnets.
Abstract: New scintillators for high-resolution gamma ray spectroscopy have been identified, grown and characterized. Our development efforts have focused on two classes of high-light-yield materials: europium-doped alkaline earth halides and cerium-doped garnets. Of the halide single crystals we have grown by the Bridgman method-SrI2, CaI2, SrBr2, BaI2 and BaBr2-SrI2 is the most promising. SrI2(Eu) emits into the Eu2+ band, centered at 435 nm, with a decay time of 1.2 mus and a light yield of up to 115,000 photons/MeV. It offers energy resolution better than 3% FWHM at 662 keV, and exhibits excellent light yield proportionality. Transparent ceramic fabrication allows the production of gadolinium- and terbium-based garnets which are not growable by melt techniques due to phase instabilities. The scintillation light yields of cerium-doped ceramic garnets are high, 20,000-100,000 photons/MeV. We are developing an understanding of the mechanisms underlying energy dependent scintillation light yield non-proportionality and how it affects energy resolution. We have also identified aspects of optical design that can be optimized to enhance the energy resolution.
232 citations
TL;DR: In this paper, the experimental setup for the basic ammonothermal growth of GaN and the introduction of a silver capsule into the autoclave have yielded an ultrahigh purity (UHP) growth environment with reproducible external wall temperature profiles to within the error of the thermocouples (type K with special limits of error (SLE), ±2.5°C).
69 citations
TL;DR: In this paper, the authors performed optical transmission measurements on high quality bulk gallium nitride (GaN) crystals grown by sodium flux, hydride vapor phase epitaxy, and the ammonothermal method with varying free electron concentrations ranging from 4×10 16 ǫ −3 to 9×10 18ǫ -3.
46 citations
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TL;DR: In this paper, the authors summarized the key advantages of using quantum dots as luminophores in light-emitting devices (LEDs) and outlined the operating mechanisms of four types of QD-LEDs.
Abstract: This Review article summarizes the key advantages of using quantum dots (QDs) as luminophores in light-emitting devices (LEDs) and outlines the operating mechanisms of four types of QD-LED. The key scientific and technological challenges facing QD-LED commercialization are identified, together with on-going strategies to overcome these challenges.
2,086 citations
TL;DR: In this article, the characteristics and commercial status of both vertical and lateral GaN power devices are reviewed, providing the background necessary to understand the significance of these recent developments and the challenges encountered in GaN-based converter design, such as the consequences of faster switching on gate driver and board layout.
Abstract: Gallium nitride (GaN) power devices are an emerging technology that have only recently become available commercially. This new technology enables the design of converters at higher frequencies and efficiencies than those achievable with conventional Si devices. This paper reviews the characteristics and commercial status of both vertical and lateral GaN power devices, providing the background necessary to understand the significance of these recent developments. In addition, the challenges encountered in GaN-based converter design are considered, such as the consequences of faster switching on gate driver design and board layout. Other issues include the unique reverse conduction behavior, dynamic $R_{\mathrm {{ds}},\mathrm {{on}}}$ , breakdown mechanisms, thermal design, device availability, and reliability qualification. This review will help prepare the reader to effectively design GaN-based converters, as these devices become increasingly available on a commercial scale.
769 citations
TL;DR: This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce3+-doped garnet phosphors, and summarize previous research on the structural design and optical properties of garnet phosphate materials to discuss future research opportunities.
Abstract: Garnets have the general formula of A3B2C3O12 and form a wide range of inorganic compounds, occurring both naturally (gemstones) and synthetically. Their physical and chemical properties are closely related to the structure and composition. In particular, Ce3+-doped garnet phosphors have a long history and are widely applied, ranging from flying spot cameras, lasers and phosphors in fluorescent tubes to more recent applications in white light LEDs, as afterglow materials and scintillators for medical imaging. Garnet phosphors are unique in their tunability of the luminescence properties through variations in the {A}, [B] and (C) cation sublattice. The flexibility in phosphor composition and the tunable luminescence properties rely on design and synthesis strategies for new garnet compositions with tailor-made luminescence properties. It is the aim of this review to discuss the variation in luminescence properties of Ce3+-doped garnet materials in relation to the applications. This review will provide insight into the relation between crystal chemistry and luminescence for the important class of Ce3+-doped garnet phosphors. It will summarize previous research on the structural design and optical properties of garnet phosphors and also discuss future research opportunities in this field.
762 citations
TL;DR: Solution-processable halide perovskites have high luminous efficiency and excellent chemical tunability, making them ideal candidates for light-emitting diodes, and Yang et al. achieve high external quantum efficiency of 14% in the devices by fine-tuning the phase and passivating the surface defects.
Abstract: Perovskite light-emitting diodes (LEDs) are attracting great attention due to their efficient and narrow emission. Quasi-two-dimensional perovskites with Ruddlesden–Popper-type layered structures can enlarge exciton binding energy and confine charge carriers and are considered good candidate materials for efficient LEDs. However, these materials usually contain a mixture of phases and the phase impurity could cause low emission efficiency. In addition, converting three-dimensional into quasi-two-dimensional perovskite introduces more defects on the surface or at the grain boundaries due to the reduction of crystal sizes. Both factors limit the emission efficiency of LEDs. Here, firstly, through composition and phase engineering, optimal quasi-two-dimensional perovskites are selected. Secondly, surface passivation is carried out by coating organic small molecule trioctylphosphine oxide on the perovskite thin film surface. Accordingly, green LEDs based on quasi-two-dimensional perovskite reach a current efficiency of 62.4 cd A−1 and external quantum efficiency of 14.36%.
719 citations
TL;DR: The state-of-art progress on this novel family of luminescent materials is summarized and the topics of materials discovery, crystal chemistry, structure-related luminecence, temperature-dependent luminescence, and spectral tailoring are discussed.
Abstract: Advances in solid state white lighting technologies witness the explosive development of phosphor materials (down-conversion luminescent materials). A large amount of evidence has demonstrated the revolutionary role of the emerging nitride phosphors in producing superior white light-emitting diodes for lighting and display applications. The structural and compositional versatility together with the unique local coordination environments enable nitride materials to have compelling luminescent properties such as abundant emission colors, controllable photoluminescence spectra, high conversion efficiency, and small thermal quenching/degradation. Here, we summarize the state-of-art progress on this novel family of luminescent materials and discuss the topics of materials discovery, crystal chemistry, structure-related luminescence, temperature-dependent luminescence, and spectral tailoring. We also overview different types of nitride phosphors and their applications in solid state lighting, including general ...
538 citations