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Metal‐polar InN quantum dots (QDs) are grown by metalorganic chemical vapor deposition at temperatures between 500 and 600 °C. Dot densities between 4 × 108 and 4 × 1010 cm−2 are observed. InN QDs exhibit room‐temperature photoluminescence (PL) with peak wavelengths from 1100 to >1550 nm. GaN cap layers grown on InN QDs have little effect on either peak PL wavelength or intensity, a step toward creating multilayer structures for InN QD devices. [ABSTRACT FROM AUTHOR]

The author discusses the story behind the invention of blue light-emitting diode .Topics include the progress made in combining white LED to blue LED using yellow phosphor, the material properties of indium gallium nitride as well as metal organic chemical vapor deposition as candidates for the development of blue LED and the future challenges of blue LED in the field of electronic. The author Shuji Nakamura, a Japanese physicist and the inventor of blue LED presents his autobiography.

Shuji Nakamura discovered p-type doping in Gallium Nitride (GaN) and developed blue, green, and white InGaN based light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid-state lighting systems and enabled the next generation of optical storage. Together with Isamu Akasaki and Hiroshi Amano, he is one of the three recipients of the 2014 Nobel Prize in Physics. In his Nobel lecture, Shuji Nakamura gives an overview of this research and the story of his inventions. [ABSTRACT FROM AUTHOR]

Shuji Nakamura discovered p-type doping in Gallium Nitride (GaN) and developed blue, green, and white 'InGaN-based' light emitting diodes (LEDs) and blue laser diodes (LDs). His inventions made possible energy efficient, solid-state lighting systems and enabled the next generation of optical storage. In this biography, Shuji Nakamura tells the story of his personal life and his scientific career. [ABSTRACT FROM AUTHOR]

Metasurface‐based optical elements offer a wide design space for miniature and lightweight optical applications. Typically, metasurface optical elements transform an incident light beam into a desired output waveform. Recent demonstrations of light‐emitting metasurfaces highlight the potential for directly producing desired output waveforms via metasurface‐mediated spontaneous emission. In this work, reciprocal finite‐difference time‐domain (FDTD) simulations and machine learning are used to enable the inverse design of highly unidirectional photoluminescent III‐Nitride quantum well metasurfaces capable of directive p‐, s‐, or combined p‐ and s‐ polarized emission at arbitrary angles. In comparison with previous intuition‐guided designs using the same quantum well architectures, the inverse design approach enables new polarization capabilities and experimentally demonstrated improvements in directivity of 54%. An analysis of ways in which the inverse design both validates and contradicts previous intuition‐guided design heuristics is presented. Ultimately, the combination of reciprocal simulations and efficient global optimization (EGO) grants remarkable improvements in emission directivity and results in full control over the polarization and momentum of emitted light, including simultaneous directional emission of s‐ and p‐polarized light. [ABSTRACT FROM AUTHOR]

High output InGaN single quantum well type blue and green light emitting diodes (LEDs) with an optical output of between 3 and 5 mW have been developed and commercialized. The differences in peak absorption energy and light emitting energy for the blue and green LEDs were 290 and 570 meV. These values indicate that the LED or laser emission is generated from a deep localized level in an InGaN well layer. An InGaN multiple quantum well laser diode was developed that oscillated continuously at room temperature for more than 300 hours. The preliminary characteristics are an output of 50 mW, an operating temperature of 100 °C, a characteristic temperature of 170 K, and an oscillation wavelength of 416 nm. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(5): 1–8, 1998 [ABSTRACT FROM AUTHOR]

Review: 49 refs. [ABSTRACT FROM AUTHOR]

Scanning tunneling electroluminescence (STL) microscopy is performed on a 3 nm‐thick InGaN/GaN quantum well (QW) with [In] = 0.23 such that the main light emission occurs in the green. The technique is used to map the radiative recombination properties at a scale of a few nanometers and correlate the local electroluminescence map with the surface topography simultaneously imaged by scanning tunneling microscopy. While the expected green emission is observed all over the sample, measurements performed on a 500 nm × 500 nm area around a 150 nm‐large and 2.5 nm‐deep hexagonal defect reveal intense emission peaks at higher energies close to the defect edges, features which are not visible in the macrophotoluminescence spectrum of the sample. Via a fitting of the local tunneling electroluminescence spectra, quantitative information on the fluctuations of the intensity, peak energy, width, and phonon replica intensity of the different spectral contributions is obtained, which provides information on carrier localization in the QW. This procedure also indicates that the carrier diffusion length on the probed area of the QW is shorter than 50 nm. [ABSTRACT FROM AUTHOR]

Scanning near-field and time-resolved photoluminescence spectroscopy have been applied to characterize single m-plane InGaN QW structures. The PL spectra were found to be formed by emission from the extended and the localized states. Lateral dimensions of uniform potential regions were placed around a few tens of nm. It was shown that optimization of the template for the QW growth results in a more uniform emission spectrum and a reduced effect of carrier localization. The radiative recombination time at low temperatures was found to be short, about 0.5 ns. At room temperature, nonradiative recombination via efficient recombination centres was prevailing. Complexes of Ga vacancies with O were suggested to play this role. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]

Investigations of the use of patterned porous GaN underlayers to achieve elastic relaxation of lattice‐mismatched top layers such as InGaN and AlGaN are reviewed. Thereby, the degree of relaxation of the top layers increases with the porosity and associated decrease in mechanical hardness of the porous GaN underlayers as well as with decreasing pattern size and increase in thickness of the lattice‐mismatched top layers, following the trends observed for nanostructures. Micrometer‐sized, high‐fill‐factor GaN‐on‐porous‐GaN tile arrays are used as universal substrate for the deposition of InGaN and AlGaN. Due to the elastic nature of the relaxation process, the threading dislocation density in the epitaxial material grown on top of the GaN‐on‐porous‐GaN tiles is equivalent to that in the GaN base material. InGaN and AlGaN layers grown on top of relaxed or partially relaxed InGaN or AlGaN underlayers by metal–organic chemical vapor deposition display a higher indium or aluminum content compared to their counterparts deposited on coloaded planar GaN reference wafers due to the decreased lattice mismatch. First applications of the patterned porous GaN‐based technology for optoelectronic and electronic devices are presented and serve as a pathway toward future implementations. [ABSTRACT FROM AUTHOR]

Laser lighting systems can take many form factors for applications, such as spotlighting, general illumination, or decorative lighting. The use of lasers in conjunction with phosphors for white lighting leads to questions about incorporating the various package elements. Some practical considerations of a transmission geometry system implementing a blue laser and a yellow Ce:YAG single crystal phosphor are discussed, with specific focus on color tuning and the optical efficiency of the single crystal. A compact emitter is demonstrated with examples of modifications to increase the system performance and complexity. Moving from a cool white system to a warm white system is done through the addition of a red light such as a red laser or red phosphor. The single crystal phosphor component needs to allow light to be coupled in from the laser and has high extraction efficiency. A wavelength‐selective reflective coating is implemented to address these concerns, which increases the luminous efficacy of the system. Engineering the phosphor element using this concept may allow for single crystal phosphors to be viable options for future laser lighting systems. [ABSTRACT FROM AUTHOR]

Blue (2021¯) semipolar vertical‐cavity surface‐emitting lasers with a buried tunnel junction current aperture are demonstrated under continuous‐wave operation with a differential efficiency of 4% and a threshold current of 2.7 mA for a lasing mode at 452 nm. The effects of the aperture diameter on these 9λ cavity length devices are presented, showing that the differential efficiency increases with aperture size, whereas the threshold current density remains constant for apertures larger than 10 μm. Filamentary lasing is observed in the larger aperture sizes, and it is suggested that this mode behavior is due to current injection inhomogeneity across the aperture. This theory is supported by the correlation between optical nearfield images and thermal microscopy images. [ABSTRACT FROM AUTHOR]

A heterogeneously integrated InGaN laser diode (LD) on Si is proposed as a path toward visible wavelength photonic integrated circuits (PICs) on Si. Herein, InGaN films are vertically stacked on a TiO2 waveguide (WG) fabricated on a Si wafer by bonding. In the light propagation direction, it is composed of a hybrid InGaN/TiO2 section, a TiO2 WG, an adiabatic taper, and mirrors that can form a cavity. As the refractive index of GaN is well matched with that of TiO2, the optical transverse mode extends to both the GaN and TiO2 in a hybrid mode. Modes between a hybrid InGaN/TiO2 and a pure TiO2 WG can transfer with an adiabatic taper structure. The coupling loss is calculated to be less than 0.5 dB with fairly short taper length of 78 μm and tip width of 200 nm. GaN substrate removal and bonding are critical fabrication steps of this LD and PIC. The substrate removal is successfully done by photoelectrochemical etching. Although direct bonding of GaN wafers with thermal oxide on Si is successful, GaN epitaxial wafers are more difficult. An implication and remedy of this is discussed in terms of surface roughness of GaN epitaxial film. [ABSTRACT FROM AUTHOR]

The finite element method was used to determine the thermal resistance of a flip-chip-bonded GaN-based vertical-cavity surface-emitting laser (VCSEL) with substrate removal and dielectric distributed Bragg reflectors (DBRs). In this work, we investigate the effects of the DBR configuration, mask layer alignment tolerances, aperture diameters, and cladding layer thicknesses on the thermal properties of the flip-chip design. The current flip-chip design suffers from high thermal resistance (∼4600 K W−1). By reducing the mask layer alignment tolerances and increasing the cladding thickness, the thermal resistance values could be made comparable to devices reported in the literature that achieved CW operation at room temperature (∼3000 K W−1). Low thermal resistance designs are critical to achieve CW operation and mitigate the effects of thermal roll-over in flip-chip GaN-based VCSELs. [ABSTRACT FROM AUTHOR]

Group III impurity doped ZnO thin films were deposited on MgAl2O3 substrates using a simple low temperature two-step deposition method involving atomic layer deposition and hydrothermal epitaxy. Films with varying concentrations of either Al, Ga, or In were evaluated for their optoelectronic properties. Inductively coupled plasma atomic emission spectroscopy was used to determine the concentration of dopants within the ZnO films. While Al and Ga-doped films showed linear incorporation rates with the addition of precursors salts in the hydrothermal growth solution, In-doped films were shown to saturate at relatively low concentrations. It was found that Ga-doped films showed the best performance in terms of electrical resistivity and optical absorbance when compared to those doped with In or Al, with a resistivity as low as 1.9 mΩ cm and an optical absorption coefficient of 441 cm−1 at 450 nm. [ABSTRACT FROM AUTHOR]

Aims/Introduction This trial assessed the efficacy and safety of the possibility of varying the daily injection time of once-daily, long-acting basal insulin degludec ( IDeg) in Japanese patients with type 2 diabetes inadequately controlled with insulin glargine. Materials and Methods This was a 26-week, multicenter, open-label, randomized, treat-to-target trial, with a 2 × 2 factorial design comparing IDeg flexible (allowing dosing ±8 h from an agreed dosing time) with IDeg fixed dosing (at the same time each day). It was carried out in 458 adult patients who were inadequately controlled on insulin glargine with or without oral antidiabetic drugs. Results The majority of doses were taken within 2 h of the agreed dosing time, showing a high level of adherence among Japanese patients. After 26 weeks, IDeg flexible was non-inferior to IDeg fixed with respect to change in glycated hemoglobin from baseline, estimated treatment difference 0.08% points (95% confidence interval −0.05; 0.22). Fasting plasma glucose decreased to a similar level with IDeg flexible and IDeg fixed, estimated treatment difference −0.18 mmol/L (95% confidence interval −0.48; 0.12). The rates of confirmed and nocturnal confirmed hypoglycemia were numerically, but not significantly, higher with IDeg flexible vs IDeg fixed dosing. The rates of adverse events with IDeg flexible and IDeg fixed dosing were similar. Conclusions These results showed the efficacy and safety of allowing patients to vary the time they dosed IDeg, when necessary, in Japanese patients with type 2 diabetes. Dosing of IDeg at a time convenient to the patient was non-inferior, with respect to glycated hemoglobin, to dosing at the same time each day. [ABSTRACT FROM AUTHOR]

We estimate the roughening-induced scattering optical losses in III-nitride current aperture laser diodes (CA-LDs) caused by imperfect photoelectrochemical (PEC) etching of the active region of a [ABSTRACT FROM AUTHOR]

We have previously shown that xenogeneic stromal cell stimulation of naïve T cells resulted in the generation of a new type of regulatory T (Treg) cell termed HOZOT, which has multifunctional properties and a CD4/CD8 double-positive phenotype. Even after the establishment of HOZOT, stromal cells can function as an antigen-presenting cell (APC) by inducing these cells to produce interleukin (IL)-10. When compared with other stimuli, stromal cells showed an IL-10-producing ability comparable to anti-CD3 antibody (Ab) stimulation, and much greater than dendritic cell (DC) stimulation. Distinct from professional APCs, stromal cells express only major histocompatibility complex (MHC) class I and B7-1 costimulatory molecules, and not MHC class II or other costimulatory molecules, such as ICOSL (CD275), PD-L1 (CD274), PD-L2 (CD273), CD40, OX40L (CD252) and 4-1BBL (CD137L) in the absence of stimulation. Blocking experiments revealed that, in addition to anti-H-2Kd Ab and anti-human CD8 Ab, anti-mouse B7-1 Ab could effectively block IL-10 production, indicating a key role of the B7-1/CD28 pathway. Using stromal cells expressing different levels of B7-1, IL-10 production correlated with the levels of B7-1 expression. Distinct from ICOSL or PD-L1 expressed on DCs (which are regarded as IL-10-inducing costimulatory molecules), this study showed that B7-1 on stromal cells is a key molecule regulating IL-10 production by multifunctional Treg cells, HOZOT. [ABSTRACT FROM AUTHOR]

A compositionally step‐graded (CSG) InGaN barrier is designed for the active region of c‐plane blue light‐emitting diodes (LEDs). High external quantum efficiencies of 45, 42, 39 and 36% are achieved at current densities of 100, 200, 300 and 400 A/cm2, respectively. Compared with GaN barrier devices, LEDs with CSG InGaN barriers showed higher power, lower operating voltage and smaller wavelength blueshift, compared with GaN barrier LEDs. Owing to the low‐voltage performance, higher wall‐plug efficiency can be achieved for blue LEDs with CSG InGaN barriers. [ABSTRACT FROM AUTHOR]

By means of time-resolved emission spectroscopy, the emission dynamics of InGaN quantum well light-emitting devices is evaluated. The localization, radiation, and nonradiating recombination processes of the exciton are evaluated. It is found that there exist random potential fluctuations in the quantum well in samples with less than about 10% In in the InGaN activation layer. By means of these fluctuations, localization of the excitons can be attained. It is also found that the degree of localization increases as the In composition is increased, and that quantum dot-like regions are naturally formed in samples with an In content of more than about 20%. It is found that the capture of excitons by nonradiating recombination centers is suppressed and that a high-emission quantum efficiency is realized by such a pronounced localization. © 1998 Scripta Technica, Electron Comm Jpn Pt 2, 81(7): 45–56, 1998 [ABSTRACT FROM AUTHOR]

B Laser Lighting b In article number 2000391 by Caroline E. Reilly and coworkers, a compact emitter for a laser lighting system is created using a commercial nitride laser diode, a small single crystal phosphor, and in-house machined parts. Variations to improve color and efficiency are considered via experiment and simulation, including the addition of a red laser, a red phosphor, or a wavelength-selective coating. [Extracted from the article]

The effects of several design geometries on the thermal resistance for a flip‐chip GaN‐based VCSEL with dielectric distributed Bragg reflectors was studied by Mishkat‐Ul‐ Masabih (article no. 1600819) using finite‐element analysis. The current flip‐chip design suffers from high thermal resistance, preventing devices to lase under CW operation. It was found that including a patterned DBR with recessed metal, reducing the lithography alignment tolerances, and increasing the aperture size; all contributed to the reduction of the thermal resistance of the design. In addition, epitaxially increasing the cladding layer thickness on either side of the active region also lowered the thermal resistance significantly. The thermal resistance values for previously reported CW device configurations were also calculated and compared to our flip‐chip design. The internal temperature changes at the threshold were estimated for the devices, indicating why previous generations of our flip‐chip devices could not achieve CW lasing. Combining these techniques, the effects of thermal roll‐over can be mitigated; as the reduction of the device temperature is a key consideration for obtaining high output power CW GaN‐based VCSELs. [ABSTRACT FROM AUTHOR]

Constricting the current to flow to the center of the lasing mode by laterally and controllably etching the active region can improve the performance of optoelectronic and electronic devices by eliminating current leakage pathways and reducing the attendant dc‐rf dispersion. Differently from other III‐V semiconductors, the III‐nitrides lack conventional wet etchants and photoelectrochemical (PEC) etching has been proposed as an alternative to create selective and controllable undercut. Ludovico Megalini et al. (pp. 953–957) have achieved CW operation of a III‐N current aperture blue laser diode (CALD) by PEC etching the active region of a (202̅1̅) InGaN multi quantum well (MQW) laser diode. Here they estimate the roughening‐induced scattering optical modal losses caused by imperfect PEC etching in such structure by using a 3D Volume Current Model in conjunction with roughness data obtained by AFM and SEM image processing of the remnant PEC‐etched waveguides after the top p‐layers were removed by focused ion beam cuts. Finally they propose possible ways to mitigate these scattering losses and therefore improve the differential efficiency of the final device. [ABSTRACT FROM AUTHOR]