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Hyperspectral endoscopy can offer multiple advantages as compared to conventional endoscopy. Our goal is to design and develop a real-time hyperspectral endoscopic imaging system for the diagnosis of gastrointestinal (GI) tract cancers using a micro-LED array as an in-situ illumination source. The wavelengths of the system range from ultraviolet to visible and near infrared. To evaluate the use of the LED array for hyperspectral imaging, we designed a prototype system and conducted ex vivo experiments using normal and cancerous tissues of mice, chicken, and sheep. We compared the results of our LED-based approach with our reference hyperspectral camera system. The results confirm the similarity between the LED-based hyperspectral imaging system and the reference HSI camera. Our LED-based hyperspectral imaging system can be used not only as an endoscope but also as a laparoscopic or handheld devices for cancer detection and surgery.

Time-resolved photoluminescence (PL), current-voltage characteristics and deep trap spectra of nanopillar GaN/InGaN multi-quantum-well (MQW) light emitting diodes (LEDs) prepared by reactive ion etching (RIE) from planar samples were studied as a function of post-RIE surface treatment. Immediately after RIE, we observe a sharp drop of intensity of the 460 nm MQW PL band and a strong increase of intensity of the defect-related 600 nm MQW band similar to the yellow band in n-GaN. KOH etching and (NH 4) 2 S sulfur passivation treatments increased the MQW PL band intensity above the level of the planar structure and decreased the intensity of the defect 600 nm PL band, but was not effective in decreasing the RIE-induced excessive leakage current of the LEDs. Only annealing at ≥ 700 °C following RIE was able to strongly suppress the excessive leakage. Deep trap spectra suggest that the RIE-induced drop of the 460 nm PL intensity and increase of the 600 nm PL intensity are accompanied by the increase of the Ec-0.7 eV electron trap density and of Ev+0.8 eV hole trap density in the quantum wells. The first of these defects is attributed to nitrogen interstitial acceptors believed to be effective nonradiative recombination centers, while the hole traps are attributed to gallium vacancy acceptor complexes with shallow donors. Both types of defects are produced on the sidewalls of nanopillars by RIE and can be largely annealed at 700 °C, although higher annealing temperatures are needed to fully suppress their negative impact. These results are also relevant to curing the effects of dry-etch damage for micro-LEDs with small chip dimensions, a serious problem in the micro-LED field. [ABSTRACT FROM AUTHOR]

Pyramid-shaped InGaN/GaN micro-light-emitting diodes (μ-LEDs) were grown on a sapphire substrate using the selective area growth technique. A stable emission wavelength of a single μ-LED pyramid at 412 nm was observed under an injection current from 0.05 to 20 mA, despite the non-uniformity of the thickness and composition of the multiple quantum wells (MQWs) on the sidewall. An efficient carrier confinement and, thus, a high luminescence intensity were demonstrated in the middle of the sidewall through spatial-resolved cathodoluminescence (CL) characterization and were predicted by theoretical simulations. An ultra-high output power density of 1.37 kW/cm2 was obtained from the single μ-LED pyramid, illustrating its great potential for application in high-brightness micro-displays and in virtual reality and augmented reality (VR and AR) applications. [ABSTRACT FROM AUTHOR]

The micro lighting-emitting diode (Micro-LED) array devices have attracted attention due to increasing demand in augmented reality (AR), virtual reality (VR), LIFI light source, and other micro-display applications. However, with the decrease of micro-LED diameter, the performance of micro-LED is severely limited due to the size effect. In the work, the AlGaInP based red micro-LED with diameter ranging from 2 to 16 μm was prepared to study the size effect of micro-LED array, the array with larger micro-LED diameter show higher external quantum efficiency (EQE), meanwhile, the carrier lifetime decrease with the decreasing of the diameter, which can be explained by more surface states in the micro-LED with smaller diameter. The enhancement of EQE by 2 times has been achieved after surface passivation in (NH 4) 2 S x solution. • Micro-LED diameter ranging from 2 to 16 μm was fabricated, and the influence of size effect on the photoelectric performance was studied. • A fast and low-cost surface passivation method was used to successfully reduce the surface state density, and increase EQE of the Micro-LED array by 2 times. • The cause of size effect is clearly explained and the device performance is successfully optimized through surface passivation, which provides valuable guidance for the future commercialization of micro-LED. [ABSTRACT FROM AUTHOR]

Micro-light emitting diodes (Micro-LEDs) based on III-nitride semiconductors have become a research hotspot in the field of high-resolution display due to its unique advantages. However, the edge effect caused by inductively coupled plasma (ICP) dry etching in Micro-LEDs become significant with respect to the decreased chip size, resulting in a great reduction in device performance. In this article, sector-shaped GaN-based blue Micro-LEDs are designed and fabricated. Additionally, the device performance of different size Micro-LEDs with passivation are investigated with respect to those without passivation. Several methods have been applied to minimize the etching damage near the edge, including acid-base wet etching and SiO2 passivation layer growth. The room temperature photoluminescence (PL) results demonstrate that the light emission intensity of Micro-LEDs can be significantly enhanced by optimized passivation process. PL mapping images show that the overall luminescence of properly passivated Micro-LEDs is enhanced, the uniformity is improved, and the effective luminescence area is increased. The recombination lifetime of carriers in Micro-LEDs are increased by the usage of passivation process, which proves the reduction in non-radiative recombination centers in Micro-LEDs and improved luminescence efficiency. As a result, the internal quantum efficiency (IQE) is improved from 14.9% to 37.6% for 10 μm Micro-LEDs, and from 18.3% to 26.9% for 5 μm Micro-LEDs. [ABSTRACT FROM AUTHOR]

Emerging technologies, such as smart wearable devices, augmented reality (AR)/virtual reality (VR) displays, and naked-eye 3D projection, have gradually entered our lives, accompanied by an urgent market demand for high-end display technologies. Ultra-high-resolution displays, flexible displays, and transparent displays are all important types of future display technology, and traditional display technology cannot meet the relevant requirements. Micro-light-emitting diodes (micro-LEDs), which have the advantages of a high contrast, a short response time, a wide color gamut, low power consumption, and a long life, are expected to replace traditional liquid-crystal displays (LCD) and organic light-emitting diodes (OLED) screens and become the leaders in the next generation of display technology. However, there are two major obstacles to moving micro-LEDs from the laboratory to the commercial market. One is improving the yield rate and reducing the cost of the mass transfer of micro-LEDs, and the other is realizing a full-color display using micro-LED chips. This review will outline the three main methods for applying current micro-LED full-color displays, red, green, and blue (RGB) three-color micro-LED transfer technology, color conversion technology, and single-chip multi-color growth technology, to summarize present-day micro-LED full-color display technologies and help guide the follow-up research. [ABSTRACT FROM AUTHOR]

• Developing a completely new scheme for optical encryption in visible light communication. • Application of dual encryption of digital algorithm (temporal ghost imaging) and physical hardware (micro-LED). • Realizing optical communication of error-free, high robustness and high security. • Opening up a new application scenario for temporal ghost imaging. As the great application potential of visible light communication (VLC) in the next generation communication after 5G, study of the transmission security in VLC is high desirable with the rapid growth of wireless network traffic. In this paper, an optical encryption scheme for VLC is proposed based on temporal ghost imaging (TGI) with a micro-light-emitting diode (micro-LED). The target temporal signal is digitally encrypted by a sequence of randomized orthogonal secret key. The micro-LED working at 4 Gbps (over 20 times higher than its bandwidth ~160 MHz) physically encrypts the information in a non-invertible way due to the severe transmission distortion. According to TGI theory, correlation calculation between the integration value of received distorted signal and the secret key can realize the decryption process without error. The integrated encryption of digital algorithm and physical hardware property guarantee the security of this method. We experimentally demonstrate the system can resist attack of up to 40% occlusion or 80% Gaussian noise and obtain error-free signal. [ABSTRACT FROM AUTHOR]

The metal halide perovskite nanocrystal (MHP-NC), an easy-to-fabricate and low cost fluorescent material, is recognized to be among the promising candidates of the color conversion material in the micro light-emitting diode (micro-LED) display, providing that the stability can be further enhanced. It is found that the water steam, oxygen, thermal radiation and light irradiation—four typical external factors in the ambient environment related to micro-LED display—can gradually alter and destroy the crystal lattice. Despite the similar phenomena of photoluminescence quenching, the respective encroaching processes related to these four factors are found to be different from one another. The encroaching mechanisms are collected and introduced in separate categories with respect to each external factor. Thereafter, a combined effect of these four factors in an environment mimicking real working conditions of micro-LED display are also introduced. Finally, recent progress on the full-color application of MHP-NC is also reviewed in brief. [ABSTRACT FROM AUTHOR]

We describe the fabrication and characterization of matrix-addressable microlight-emitting diode (micro-LED) arrays based on InGaN, having elemental diameter of 20 μm and array size of up to 128 × 96 elements. The introduction of a planar topology prior to contact metallization is an important processing step in advancing the performance of these devices. Planarization is achieved by chemical-mechanical polishing of the SiO2-deposited surface. In this way, the need for a single contact pad for each individual element can be eliminated. The resulting significant simplification in the addressing of the pixels opens the way to scaling to devices with large numbers of elements. Compared to conventional broad-area LEDs, the micrometer-scale devices exhibit superior light output and current handling capabilities, making them excellent candidates for a range of uses including high-efficiency and robust microdisplays. [ABSTRACT FROM PUBLISHER]

Metal halide perovskites are emerging as attractive materials for light-emitting diode (LED) applications. The external quantum efficiency (EQE) has experienced a rapid progress and reached over 21%, comparable to the state of the art organic and quantum dot LEDs. For metal halide perovskites, their simple solution-processing preparation, facile band gap tunability, and narrow emission line width provide another attractive route to harness their superior optoelectronic properties for multicolor display applications. In this work, we demonstrate a high-resolution, large-scale photolithographic method to pattern multicolor perovskite films. This approach is based on a dry lift-off process which involves the use of parylene as an intermediary and the easy mechanical peeling-off of parylene films on various substrates. Using this approach, we successfully fabricated multicolor patterns with red and green perovskite pixels on a single substrate, which could be further applied in liquid crystal displays (LCDs) with blue backlight. Besides, a prototype green perovskite micro-LED display under current driving has been demonstrated.

Blue LEDs and HEMTs based on III-Nitride have been flourishing commercially across the globe, thanks largely to breakthroughs in the material quality of the wide-bandgap compound semiconductor back in the 1990s. The realizations of white-light LEDs, blu-ray systems, and lately efficient compact chargers have drastically changed the way we live and have contributed tremendously to global energy saving efforts. The maturity and diversity of modern discrete GaN-based devices open up opportunities for an integrated GaN platform with extended functionalities and applications. In this review paper, we present an overview of the monolithic and heterogeneous integration of GaN devices and components. Various methods for the integration of electronic, optoelectronic, and optical components based on GaN are discussed. [ABSTRACT FROM AUTHOR]

Optical performance in terms of light efficiency, color crosstalk and ambient contrast ratio were analyzed for blue GaN-based micro-light emitting diodes (micro-LEDs) combined with red/green quantum dots (QDs)-polymethyl methacrylate (PMMA) films. The thickness and mass ratio of QDs films are two critical factors in affecting the performance of micro-LEDs. Firstly, the precise optical modeling of QDs-PMMA films is established based on the double integrating sphere (DIS) testing system and inverse adding doubling algorithm (IADA) theory. Red and green QDs-PMMA films are composed of ZnCdSe/ZnS QDs and green ZnCdSeS/ZnS QDs, respectively. The fundamental optical parameters of QDs-PMMA films, including scattering, absorption and anisotropy coefficients, are obtained successfully. Secondly, based on these optical parameters, the Monte Carlo ray tracing method is applied to analyze the effect of a QDs-PMMA film's thickness and mass ratio on the optical performance of micro-LEDs. Results reveal that the light efficiency first increases and then decreases with the increase of a QDs film's thickness or mass ratio, owing to the scattering characteristics of QDs. Different from the variation tendencies of light efficiency, the crosstalk between adjacent pixels increases as the QDs-PMMA film's thickness or mass ratio increases, and the ambient contrast ratio is kept stable when the thickness increases. The mass ratio variation of QDs film can change the optical performance of micro-LEDs more effectively than thickness, which demonstrates that mass ratio is a more important factor affecting the optical performance of micro-LEDs. [ABSTRACT FROM AUTHOR]

• Cesium doped tungsten trioxide nanoparticles (Cs x WO 3 NPs) were adapted into LED encapsulant. • Cs x WO 3 NPs in LED encapsulant exhibits excellent shielding performance in NIR region and high visible light transmission. • Cs x WO 3 NPs are suitable for the use of small optical devices such as NIR mini- or micro- LED. Recently, near infrared LEDs have been used in small electronic devices due to the trend of manufacturing compact systems. The intensity of near infrared (NIR) optical device needs to be moderated if the chip emits too much power. In tradition, color pigments are used as additives in the encapsulant of LEDs to reduce the intensity of over irradiated NIR, a strategy which results in unaesthetic appearance. Cesium doped tungsten trioxide (Cs x WO 3) nanoparticles (NPs) have good near infrared absorption ability. Applying very few amount of Cs x WO 3 NPs into the encapsulation materials of NIR optical device can decrease NIR intensity while still maintain high visible light transmittance without losing aesthetic touch of those devices such as LED transmitters. The addition of only 0.0021 wt% Cs x WO 3 /PMA dispersion in epoxy encapsulant can drop 15.5% NIR (860 nm) intensity but barely reduce visible light (only 3.2% at 450 nm). The excellent performance of Cs x WO 3 NPs; i.e., good NIR absorption and visible light transmission properties, can be suitable for maintaining the moderate luminescence intensity of small optoelectronic devices like NIR mini- or micro- light-emitting diodes. [ABSTRACT FROM AUTHOR]

Deterministic transfer printing of solid objects has been introduced and demonstrated, where capillary force based on water droplet has been utilized. Droplets on pickup head form capillary bridges with chips to be picked, where the capillarity provides enough force to grip or lift the chip. Release or printing of chips can be achieved by simply drying droplet while the chip is in contact with receiver substrate. That is, water droplet acts as a temporary adhesive, adheres onto solid chip by capillary force, and releases it upon drying. The technique has unique features such as self-alignment during pickup, self-correction on pickup head by short exposure to water mist, and pickup capability of solids having a nonflat, corrugated surface, all of which originated from the fluidic nature of water droplet. The technique has been successfully applied for the fabrication of stretchable micro-light-emitting diode chip arrays. The proposed technique can find wide applications in many fields such as displays, sensors, printed electronics, photovoltaics, etc.

This work proposes a high-bandwidth white-light system consisting of a blue gallium nitride (GaN) micro-LED (μLED) exciting yellow-emitting CsPbBr 1.8 I 1.2 perovskite quantum dots (YQDs) for high-speed real-time visible light communication (VLC). The packaged 80 μm × 80 μm blue-emitting μLED has a modulation bandwidth of ∼160 MHz and a peak emission wavelength of ∼445 nm. The achievable bandwidth of the white-light system is up to 85 MHz in the absence of filters and equalization technology. Meanwhile, the bandwidth of the YQDs as a color converter is as high as 73 MHz with the blue GaN μLED as the pump source. A maximum data rate of 300 Mbps can be achieved by taking advantage of the high bandwidth of the white-light system using the non-return-to-zero on-off keying (NRZ-OOK) modulation scheme. The resultant bit-error rate is 2.0 × 10 -3 , well beneath the forward error correction criterion of 3.8 × 10 -3 required for error-free data transmission. In addition, the YQDs which we proposed as a color converter possess high stability for VLC. After half a year, the achievable bandwidths of the white-light system and the YQDs are still up to 83 and 70 MHz, respectively. This study provides the direction of developing high-bandwidth white-light system for both high-efficiency solid-state lighting and high-speed VLC.