Author
Tetsuo Fujii
Bio: Tetsuo Fujii is an academic researcher from University of California, Santa Barbara. The author has contributed to research in topics: Light-emitting diode & Photonic crystal. The author has an hindex of 10, co-authored 16 publications receiving 2238 citations.
Papers
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TL;DR: In this paper, an n-side-up GaN-based LED with a hexagonal "conelike" surface has been fabricated by using the laser lift-off technique followed by an anisotropic etching process to roughen the surface.
Abstract: Roughened surfaces of light-emitting diodes (LEDs) provide substantial improvement in light extraction efficiency. By using the laser-lift-off technique followed by an anisotropic etching process to roughen the surface, an n-side-up GaN-based LED with a hexagonal “conelike” surface has been fabricated. The enhancement of the LED output power depends on the surface conditions. The output power of an optimally roughened surface LED shows a twofold to threefold increase compared to that of an LED before surface roughening.
1,412 citations
TL;DR: In this paper, an extended defect density reduction in m-plane GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy was reported.
Abstract: This letter reports on extended defect density reduction in m-plane (11¯00) GaN films achieved via lateral epitaxial overgrowth (LEO) by hydride vapor phase epitaxy. Several dielectric mask patterns were used to produce 10 to 100 μm-thick, partially and fully coalesced nonpolar GaN films. X-ray rocking curves indicated the films were free of wing tilt. Transmission electron microscopy showed that basal plane stacking fault (SF) and threading dislocation (TD) densities decreased from 105cm−1 and 109cm−2, respectively, less than 3×103cm−1 and ∼5×106cm−2, respectively, in the Ga-face (0001) wing of the LEO films. SFs persisted in ⟨0001⟩-oriented stripe LEO films, though TD reduction was observed in the windows and wings. Band-edge cathodoluminescence intensity increased 2 to 5 times in the wings compared to the windows depending on the stripe orientation. SFs in the low TD density wings of ⟨0001⟩-stripe films did not appear to act as nonradiative recombination centers.
246 citations
TL;DR: In this article, epitaxial structures which modify the distribution of guided modes were introduced to enhance the potential for efficient light extraction by photonic crystal assisted gallium nitride light-emitting diodes.
Abstract: We relate the currently limited efficiency of photonic crystal (PhC)-assisted gallium nitride light-emitting diodes (LEDs) to the existence of unextracted guided modes. To remedy this, we introduce epitaxial structures which modify the distribution of guided modes. LEDs are fabricated according to this concept, and the tailored band structure is determined experimentally. We investigate theoretically the consequences of this improvement, which significantly enhances the potential for efficient light extraction by PhCs.
203 citations
TL;DR: In this article, the fabrication and study of laser lift-off GaN-based light-emitting diodes, thinned down to the microcavity regime, incorporating two-dimensional photonic crystal diffraction gratings, were reported.
Abstract: We report on the fabrication and study of laser lift-off GaN-based light-emitting diodes, thinned down to the microcavity regime, incorporating two-dimensional photonic crystal diffraction gratings. Angle-resolved measurements reveal the photonic behavior of the devices, which strongly depends on the GaN thickness. Data point out the detrimental role of metal absorption. We explore theoretically the possibility to limit this loss channel.
127 citations
TL;DR: In this article, a photoenhanced chemical wet etching technique is presented to form a roughened surface morphology with hexagonal symmetry on laser lift-off (LLO) N-face GaN grown by metalorganic chemical vapor deposition (MOCVD) was used as etch electrolyte.
Abstract: A photo-enhanced chemical wet etching technique is presented to form a roughened surface morphology with hexagonal symmetry on laser lift-off (LLO) N-face GaN grown by metalorganic chemical vapor deposition (MOCVD) An aqueous solution of KOH was used as etch electrolyte The etched surface showed cones with hexagonal pyramid structures bound by {1011} facets A detailed analysis of the etch rates and time-evolution of the surface morphology is described as a function of KOH concentration (125 M to 88 M) The comparison between (0001) N-face and Ga-face GaN etch morphology is discussed This roughened hexagonal surface morphology can be applied to enhance the external efficiency in GaN based light-emitting diodes (LEDs)
103 citations
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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: A comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods can be found in this paper, where the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronics, and energy harvesting devices.
Abstract: One-dimensional (1D) ZnO nanostructures have been studied intensively and extensively over the last decade not only for their remarkable chemical and physical properties, but also for their current and future diverse technological applications. This article gives a comprehensive overview of the progress that has been made within the context of 1D ZnO nanostructures synthesized via wet chemical methods. We will cover the synthetic methodologies and corresponding growth mechanisms, different structures, doping and alloying, position-controlled growth on substrates, and finally, their functional properties as catalysts, hydrophobic surfaces, sensors, and in nanoelectronic, optical, optoelectronic, and energy harvesting devices.
1,247 citations
TL;DR: In this paper, the authors review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges, and describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.
Abstract: Over the past decade, advances in LEDs have enabled the potential for wide-scale replacement of traditional lighting with solid-state light sources. If LED performance targets are realized, solid-state lighting will provide significant energy savings, important environmental benefits, and dramatically new ways to utilize and control light. In this paper, we review LED performance targets that are needed to achieve these benefits and highlight some of the remaining technical challenges. We describe recent advances in LED materials and novel device concepts that show promise for realizing the full potential of LED-based white lighting.
764 citations
TL;DR: In this article, a photonic-crystal structure for superior optical mode control was proposed for blue light-emitting diodes with a light extraction efficiency of 73% using InGaN-GaN devices.
Abstract: Blue light-emitting diodes with a light extraction efficiency of 73% are reported. The InGaN–GaN devices use a photonic-crystal structure for superior optical mode control; their performance has been characterized experimentally and modelled theoretically.
716 citations
TL;DR: Graphene can replace sapphire crystals as the substrate for the growth of gallium nitride layers and the layered structure of a graphene substrate made it possible to easily transfer GaN thin films and GaN-based LEDs onto foreign substrates such as glass, metal, or plastic.
Abstract: We fabricated transferable gallium nitride (GaN) thin films and light-emitting diodes (LEDs) using graphene-layered sheets. Heteroepitaxial nitride thin films were grown on graphene layers by using high-density, vertically aligned zinc oxide nanowalls as an intermediate layer. The nitride thin films on graphene layers show excellent optical characteristics at room temperature, such as stimulated emission. As one of the examples for device applications, LEDs that emit strong electroluminescence emission under room illumination were fabricated. Furthermore, the layered structure of a graphene substrate made it possible to easily transfer GaN thin films and GaN-based LEDs onto foreign substrates such as glass, metal, or plastic.
589 citations