Shuji Nakamura

Bio: Shuji Nakamura is an academic researcher. The author has contributed to research in topics: Light-emitting diode & Active layer. The author has an hindex of 1, co-authored 1 publications receiving 1592 citations.

The Roles of Structural Imperfections in InGaN-Based Blue Light-Emitting Diodes and Laser Diodes

Abstract: REVIEW High-efficiency light-emitting diodes emitting amber, green, blue, and ultraviolet light have been obtained through the use of an InGaN active layer instead of a GaN active layer. The localized energy states caused by In composition fluctuation in the InGaN active layer are related to the high efficiency of the InGaN-based emitting devices. The blue and green InGaN quantum-well structure light-emitting diodes with luminous efficiencies of 5 and 30 lumens per watt, respectively, can be made despite the large number of threading dislocations (1 x 10(8) to 1 x 10(12) cm-2). Epitaxially laterally overgrown GaN on sapphire reduces the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. InGaN multi-quantum-well structure laser diodes formed on the GaN layer above the SiO2 mask area can have a lifetime of more than 10,000 hours. Dislocations increase the threshold current density of the laser diodes.

Status and Future of High-Power Light-Emitting Diodes for Solid-State Lighting

Abstract: Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs

GaN:ZnO Solid Solution as a Photocatalyst for Visible-Light-Driven Overall Water Splitting

Abstract: Photocatalytic overall water splitting has been studied extensively from the viewpoint of solar energy conversion Despite numerous attempts, none have yielded satisfactory results for the development of photocatalysts, which work under visible light irradiation to efficiently utilize solar energy We report here the first example of visible-light-driven overall water splitting on a novel oxynitride photocatalyst, a solid solution of GaN and ZnO with a band gap of 258-276 eV, modified with RuO2 nanoparticles In contrast to the conventional non-oxide photocatalysts, such as CdS, the solid solution is stable during the overall water splitting reaction This is the first example of achieving overall water splitting by a photocatalyst with a band gap in the visible light region, which opens the possibility of new non-oxide-type photocatalysts for energy conversion

III–nitrides: Growth, characterization, and properties

Abstract: During the last few years the developments in the field of III–nitrides have been spectacular. High quality epitaxial layers can now be grown by MOVPE. Recently good quality epilayers have also been grown by MBE. Considerable work has been done on dislocations, strain, and critical thickness of GaN grown on different substrates. Splitting of valence band by crystal field and by spin-orbit interaction has been calculated and measured. The measured values agree with the calculated values. Effects of strain on the splitting of the valence band and on the optical properties have been studied in detail. Values of band offsets at the heterointerface between several pairs of different nitrides have been determined. Extensive work has been done on the optical and electrical properties. Near band-edge spectra have been measured over a wide range of temperatures. Free and bound exciton peaks have been resolved. Valence band structure has been determined using the PL spectra and compared with the theoretically calcu...

When group-III nitrides go infrared: New properties and perspectives

Abstract: Wide-band-gap GaN and Ga-rich InGaN alloys, with energy gaps covering the blue and near-ultraviolet parts of the electromagnetic spectrum, are one group of the dominant materials for solid state lighting and lasing technologies and consequently, have been studied very well. Much less effort has been devoted to InN and In-rich InGaN alloys. A major breakthrough in 2002, stemming from much improved quality of InN films grown using molecular beam epitaxy, resulted in the bandgap of InN being revised from 1.9 eV to a much narrower value of 0.64 eV. This finding triggered a worldwide research thrust into the area of narrow-band-gap group-III nitrides. The low value of the InN bandgap provides a basis for a consistent description of the electronic structure of InGaN and InAlN alloys with all compositions. It extends the fundamental bandgap of the group III-nitride alloy system over a wider spectral region, ranging from the near infrared at ∼1.9 μm (0.64 eV for InN) to the ultraviolet at ∼0.36 μm (3.4 eV for GaN...

Laser-Assisted Catalytic Growth of Single Crystal GaN Nanowires

Abstract: Xiangfeng Duan and Charles M. Lieber*Department of Chemistry and Chemical BiologyHarVard UniVersity, Cambridge, Massachusetts 02138ReceiVed October 18, 1999Herein we report the bulk synthesis of single crystalline GaNnanowires. Laser ablation of a composite target of GaN and acatalytic metal generates liquid nanoclusters that serve as reactivesites confining and directing the growth of crystalline nanowires.Field emission scanning electron microscopy (FE-SEM) showsthat the product primarily consists of wire-like structures. PowderX-ray diffraction (PXRD) analyses of a bulk nanowire samplecan be indexed to the GaN wurtzite structure, and indicate >95%phase purity. Transmission electron microscopy (TEM), conver-gent beam electron diffraction (CBED), and energy-dispersiveX-ray fluorescence (EDX) analyses of individual nanowires showthat they are GaN single crystals with a [100] growth direction.Nanostructured GaN materials have attracted extensive interestover the past decade due to their significant potential foroptoelectronics.