High-Indium (In)-content multi-quantum wells (MQWs) are generally thermally unstable due to poor crystal quality resulting from low-temperature growth. In this study, red emission was achieved by modulating trench structures using dual-colour MQW structures. Impressively, the red MQWs inside deep trenches showed excellent thermal stability despite being grown at low temperatures. After high-temperature annealing at 950 degrees C for 30 min, the photoluminescence (PL) intensity of red MQWs exhibited a significant reduction of 91.9% outside trenches, while it dropped by only 9.3% inside trenches, as confirmed by confocal PL mapping. Transmission electron microscopy results show that massive In-rich phases and stacking faults appeared in the MQWs outside trenches after annealing. By contrast, the red MQWs inside deep trenches remained intact in lattice arrangement without being significantly damaged. The superior thermal stability of red MQWs inside deep trenches was mainly attributed to the low-defect-density epitaxy of InGaN layers in strain-relaxed states.

Well -designed nocturnal light environment could boost performance on the cognitive tasks and promote sleep quality after light exposure. We optimized and fabricated a four -channel mixed white light with peak wavelengths of 429, 523, 591, and 621 nm. Comparing with common white light emitting diode (LED) (5798 K, 212.7 lx), the mixed white light has lower correlated color temperature (CCT) (2799 K), higher illuminance (356.2 lx), similar melanopic illuminance, and better color fidelity. We conducted experiments on 14 healthy young subjects (7 males and 7 females; age 18-25 years) to investigate the effects of nocturnal light environments on the cognitive performances and sleep quality. In consistent with the alpha-opic flux model, the mixed white light with higher illuminance shrinks the pupil size and has less melanopic flux, which results in more melatonin for subjects. More melatonin before sleep benefits the sleep quality by decreasing arousal times and improving sleep continuity. The higher illuminance light environment also promotes the inhibition ability and working memory. Moreover, it presents better color discrimination and less visual fatigue. Therefore, the lower CCT with higher illuminance nocturnal light environment effectively promotes both cognitive performances in the evening and the following sleep quality.

Small‐size pixels and high efficiency under low injection levels are required for high‐resolution microdisplay. Efficient blue InGaN micro‐light‐emitting diodes (μLEDs) with 5 μm diameter are fabricated using AuSn flip‐chip bonding, high reflection electrodes, and large‐area N electrodes surrounding the mesas. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 13.67% at a current density of 5.4 A cm −2 . Moreover, at a current density of 0.1 A cm −2 , EQE can still reach 11.69%. The electrical efficiency approaches 1, and the differential slope of log L versus log I is close to 1 at low current density. These results suggest significant progress in exploring high‐efficiency 5 μm InGaN blue μLEDs.

Carrier localization leads to efficient emission in InGaN/GaN multi-quantum wells (MQWs), especially in the long-wavelength range. Nanostructures in MQWs can facilitate the formation of carrier localization centers. In this work, high-density V-pits and trench structures were introduced in MQWs by constant low-temperature growth. Isolated red MQWs were achieved due to the carrier blocking effect caused by the V-pits and trench structures. Meanwhile, the V-pits and trench structures caused significant stress relaxation in MQWs. The topmost quantum wells (QWs) achieved red emissions due to the composition-pulling effect, while the bottom QWs exhibited green emissions. In electroluminescence measurement, a single red emission peak appeared at 636 nm at 0.1 A/cm(2). Temperature-dependent photoluminescence (PL) results showed that the PL integral intensity of the red MQWs at room temperature is about 11.32% of that at 6 K, while that of the green MQWs is only 0.09%. The PL lifetime for red emissions was more than 20 times longer than that for green ones. This study presents a new method to achieve carrier localization in red MQWs to minimize defect-related effects. (c) 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement

This study establishes a unified framework for interpreting dynamic capacitive responses in InGaN-based light-emitting diodes (LEDs) through forward-bias capacitance-voltage-frequency spectroscopy. A hybrid impedance model integrating series RL components and parallel C-G networks was developed to resolve distinct frequency-dependent capacitive regimes. The low-frequency regime (<1 kHz) is governed by interfacial capacitance with characteristic reciprocal frequency dependence, while the mid-frequency range(10 kHz-6.4 MHz) demonstrates carrier diffusion and recombination dynamics. At MHz frequencies, negative capacitance manifests due to delayed carrier emission mediated by deep-level traps. The model achieved sub-1

Trench defects in multi-quantum wells (MQWs) have been considered as flawed structures that severely degrade the internal quantum efficiency of light-emitting diodes (LEDs) in the past. In this research, trench defects are innovatively modulated into the structure to enhance the efficiency of red InGaN LEDs. Specifically, dual-color MQWs structures are grown with green MQWs at the bottom and red MQWs at the top. When high-density trench defects are introduced into the green MQWs, the upper red MQWs exhibit a significant wavelength redshift of 68 nm and approximately 6-fold luminescence enhancement compared to those without trench defects. The wavelength redshift is attributed to the increased indium incorporation due to the strain relaxation effect of trench defects. Moreover, the luminescence enhancement originates from the strong emission of the red MQWs inside trench defects. The mechanisms behind the superior luminescent properties of red MQWs within trench defects are explored in detail. Red InGaN LEDs with an internal quantum efficiency of 16.4 are achieved by modulating the trench defects. The method of achieving InGaN-based red emission by introducing trench defects is simple and reproducible, requiring no additional substrate designs. This research provides a novel pathway toward achieving high-efficiency red InGaN LEDs.

The blue-light hazard (BLH) has raised concerns with the increasing applications of white light-emitting diodes (LEDs). Many researchers believed that the shorter wavelength or more light components generally resulted in more severe retinal damage. In this study, based on the conventional phosphor-coated white LED, we added azure (484 nm), cyan (511 nm), and red (664 nm) light to fabricate the low-hazard light source. The low-hazard light sources and conventional white LED illuminated 68 Sprague–Dawley (SD) rats for 7 days. Before and after light exposure, we measured the retinal function, thickness of retinal layers, and fundus photographs. The expression levels of autophagy-related proteins and the activities of oxidation-related biochemical indicators were also measured to investigate the mechanisms of damaging or protecting the retina. With the same correlated color temperature (CCT), the low-hazard light source results in significantly less damage on the retinal function and photoreceptors, even if it has two times illuminance and blue-light hazard-weighted irradiance ( E_B ) than conventional white LED. The results illustrated that E_B proposed by IEC 62471 could not exactly evaluate the light damage on rats’ retinas. We also figured out that more light components could result in less light damage, which provided evidence for the photobiomodulation (PBM) and spectral opponency on light damage.

Herein, a research is conducted on a AlGaN/GaN photoanode by depositing AlGaN with different thicknesses on the GaN epitaxial layer. The result shows that GaN with a thin AlGaN coating has significant enhancement on water‐splitting performance. The photocurrent of GaN photoanode with 5 nm AlGaN layer can be enhanced by a factor of 1.8, compared with planar GaN. The high performance of the AlGaN/GaN heterojunction photoanode is mainly attributed to the high electron–hole density generated at the interface between GaN and AlGaN layers and the quantum tunneling transport of photogenerated carriers. The high concentration of carriers can not only enhance the mobility of carriers but also increase the electron–hole pairs for the water oxidation reaction. The quantum tunneling effect can facilitate the carriers through the high‐energy barrier of AlGaN for photolysis reaction with electrolyte. Herein, a promising method for the application of GaN in efficient water splitting is provided.

The circadian effect and photobiological safety of the display should be concerned, as well as the color gamut. By adding another primary color to the traditional blue-green-red (RGB) direct emission display, a four-primary-color display was proposed. The display presents wide color gamut and high stability with variation of pri-mary colors. The optimal color gamut coverage (CGC) in Rec. 2020 standard reaches 98.2 %, and it also maintains above 96.5 % with 20 nm variation of peak wavelengths and full widths at half maximum (FWHMs). At D65 white point, the melanopic efficacy of luminous radiation (MELR) of four-primary-color display decreases to 0.60, which is 29.4 % and 43.9 % less than liquid crystal display (LCD) and organic light-emitting diode (OLED) display, respectively. Presenting ten reference colors, the MELRs of four-primary-color display are also less than other displays in most cases. In addition, the blue light hazard efficiency of radiation (BLHER) of four-primary-color display is slightly less than other displays. At last, the further improvement for the four-primary-color display was discussed.

Light is effective to suppress the melatonin and affects the non-visual responses. The relationship between light conditions and melatonin suppression is significant when designing light environments. Based on the α-opic illuminances of five fundus photoreceptors, various previous models are built to fit and predict the experimental melatonin suppression. In this study, we present models based on α-opic fluxes, which are products of α-opic illuminances and pupil areas, to improve the fitting results of the experimental melatonin suppression. For 30- and 90-min light exposures, the α-opic flux models present higher adjusted R-squared and lower root mean square of error (RMSE) when fitting the experimental melatonin suppression, regardless of pupil dilation or not. The α-opic flux models also explain the spectral opponency on melatonin suppression. According to the residuals between predicable and experimental melatonin suppression, the effects of pupil dilation, type of light source, and subject's age are further discussed. The subject's age has little effect on the melatonin suppression. The α-opic flux models decrease the fitting residuals under different conditions, improving the applicability of the fitting models on melatonin suppression.

Nanorod array and planar green-emission InGaN/GaN multi-quantum well (MQW) LEDs were fabricated by lithography, nano-imprinting, and top–down etching technology. The defect-pinning effect of the nanostructure was found for the first time. The ratio of the bright regions to the global area in the panchromatic CL images of green MQW samples increased from 30% to about 90% after nano-fabrication. The overall luminous performance significantly improved. Throughout temperature-dependent photoluminescence (TDPL) and time-resolved PL (TRPL) measurements, the migration and recombination of carriers in the MQWs of green LEDs were analyzed. It was proved that nanostructures can effectively prevent carriers from being captured by surrounding nonradiative recombination centers. The overall PL integral intensity can be enhanced to above 18 times. A much lower carrier lifetime (decreasing from 91.4 to 40.2 ns) and a higher internal quantum efficiency (IQE) (increasing from 16.9% to 40.7%) were achieved. Some disputes on the defect influence were also discussed and clarified.

The spectral transmittance of ocular media on the short-wavelength light is higher for young observers than elders. It is essential to concentrate on the photobiological safety of children and circadian effect of elders when designing the light sources. In this study, we optimized the peak wavelengths and ratios of four-channel light emitting-diodes (LEDs), to fabricate the dynamic white light which performed well on photobiological safety, circadian effect, and color rendition for observers of different ages. Based on the optimal results, we selected the four monochromatic LEDs of 461.0, 525.0, 589.0, and 660.0 nm, and then fabricated the practical white light. The correlated color temperature (CCT) of the dynamic white light is tunable from 2700 to 6500 K. For 1-year-old observers, the blue light hazard efficiency of radiation (BLHER) is less than 0.237. For 70-year-old observers, the melanopic efficacy of luminous radiation (MELR) reaches 0.987 mW/lm and its tunability is optimized to be 2.10. The general color rendering index (Ra), special color rendering index (R9), color fidelity index (Rf), and color gamut index (Rg) are more than 89.3, 79.1,81.7, and 93.6, respectively. At last, we also discussed the impacts of the peak wavelength variation on the performances of hybrid white light.

Localized surface plasmon (LSP) coupling with many radiators are investigated. The LSP is generated by excitation of laser or electron beam on the random Ag nano particles (NPs) and arrayed ones embedded in the p-GaN of green LEDs. They couple with the excitons or radiative recombination in the quantum well (QW) and electron beam, which enhance or suppress the luminescence of the radiators. The photoluminescence (PL) intensity of periodic Ag NPs can get as much as 4.5 times higher than that of bare LED. In addition to the periodic structure, the morphology of Ag NPs also affects the localized SP (LSP) resonance intensity and light scattering efficiency. In the finite difference time domain (FDTD) simulation, five x-polarized dipoles are approximated to five quantum wells. Considering the interaction between the five dipoles and their feedback effect on LSP, the enhancement effect of SP dipole coupling with Ag NPs is amplified and the energy dissipation is reduced. The enhancement of cathodoluminescence (CL) was also found in green LEDs with Ag NPs. The three-body model composed of two orthogonal dipoles and an Ag NP is used for 3D FDTD simulation. The LSP-QWs coupling effect is separated from the electron beam (e-beam)-LSP-QW system by linear approximation. Under the excitation of electron beam, the introduction of z-dipole greatly reduces the energy dissipation. In the cross-sectional sample, z-polarized dipoles in QWs show more coupling strength to the dipole and quadrupole modes of LSP. The perturbation theory is used to separate the LSP coupling effects to x-dipole and z-dipole. At last, the resonator and the antenna effects are discussed for LSP coupling at different positions to the Ag NP.

In this study, we propose a low-cost, simple and feasible post-processing approach to improve the light extraction efficiency (LEE) of LED packages. Amorphous photonic structures (APSs) with only short-range order are fabricated from anodic aluminum oxide (AAO) and transferred to intermediate polymer stamp (IPS) by nanoimprint technology. The IPS with APSs is directly mounted onto the surface of an LED package, where the LEE is achieved as 94.6%. The scanning electron microscope (SEM) images of AAO templates and imprinted IPS are analyzed by radial distribution function and diameter histogram. The far-field patterns of APS-mounted LED packages are measured in electroluminescence (EL). The three-dimensional finite-difference time-domain (3D-FDTD) calculations of transmittance of APSs confirm that they improve the light extraction above the critical angle. Two-dimensional Fourier power spectra from SEM images of APSs are also calculated. The LEE enhancement is attributed to that the APSs have short-range order on a length scale comparable to emission wavelength of LED. We provide novel multistage simulations in a simplified FDTD model for the LED package. Finally, we discuss the influence of the morphology of APSs on the LEE of the APS mounted LEDs.

Micro-LEDs can work under an extremely high injection level and are widely used in high-brightness micro-displays and visible light communication. With the increase of carrier concentration, many-body effects gradually become important factors affecting devices' characteristics. Considering the effects of carrier scattering, bandgap renormalization, and Coulomb enhancement (CE), changes in the electroluminescence spectra of micro-LEDs are analyzed as the current density increases from 49.2 to 358.2 kA/cm2, the latter representing an ultra-high injection level. Affected by plasma screening, CE decreases below about 150 kA/cm2. After that, polarization screening dominates and effectively alleviates the spatial separation of electrons and holes, which results in CE increases to the maximum injection level of 358.2 kA/cm2. It is established that CE promotes radiative recombination processes. Different from the traditional phenomenon of "efficiency droop", the enhanced attraction between carriers leads to an abnormal increase of external quantum efficiency at high current density.

The continuous miniaturization and integration of pixelated devices have become a main trend in the field of display. Micro light-emitting diode (micro-LED) display is composed of an array of LEDs that are sub-50-micrometers in length. It has huge advantages in brightness, resolution, contrast, power consumption, lifetime, response speed and reliability compared with liquid crystal display (LCD) and organic LED (OLED) display. Consequently, micro-LED display is regarded as the next-generation display technology with high potential applications, such as virtual reality (VR), augmented reality (AR), mobile phones, tablet computers, high-definition TVs and wearable devices. Currently, the combination of commercial 5G communication technology with VR/AR display, ultra high definition video technologies will further prompt the development of micro-LED display industry. However, some basic scientific and technological problems in micro-LED display remain to be resolved. As the chip size shrinks to below 50 mu m, some problems that are not serious for large-sized LEDs appear for micro-LEDs. These problems include crystalline defects, wavelength uniformity, full-color emmision, massively tranferring and testing, etc. In the past two decades, various solutions to those problems have been proposed, which have greatly promoted the progress of micro-LED display. In this paper, an overview of micro-LED display since 2000 is given firstly, which includes the main research results and application achievements. Secondly the issues involved in the wafer epitaxy and chip process of micro-LEDs and possible solutions are discussed based on the display application in detail. The surface state induced by the dangling bonds and dry etching damages are concerned for the nonradiative recombination at a low injection level. The remedies are provided for those surface states, such as atomic-layer deposition and neutral beam etching. Some methods to reduce the threading dislocation and suppress the polarization field are summarized for micro-LED epitaxial growth. Moreover, the GaN-based LEDs on Si (100) substrate are also introduced for the future integration of micro-LEDs into the Si-based integrated circuits. As to the wavelength uniformity, the MOCVD equipment and growth technology including the laser treatment are discussed. In the chip processing part, the full-color display, mass transfer and effective inspection technology are discussed. Assembling RGB individual LEDs, quantum dot phosphor material and nanocoloumn LEDs are different routes for full-color display. Their trends in the future are provided. The pick and place, laser lift-off technologies, are strengthened in the massively transferring for micro-LEDs. In the massively and rapidly inspection technologies, the photoluminscence combined with Raman scattering, the electroluminescence combined with digital camera are discussed. Finally, the summary and outlook in these issues are also provided.

In this work, many-body effects including band-gap renormalization (BGR), Coulomb enhancement (CE) and carrier collisions (CS) are considered when the micro light emitting diode (micro-LED) operates in the injection level above 100 kA/cm2. Electroluminescence (EL) spectra of 20 micron-diameter LEDs show the redshift and broadening with current density increasing from 50 to 360 kA/cm2. An abnormal increases of external quantum efficiency (EQE) are observed above 100 kA/cm2. BGR effect combined with thermal effect lead to redshift of EL peak wavelength. Carriers collision dominates spectral width. CE enhances radiative recombination and also results in blue shift of peak wavelength.