High-performance tunnel junction (TJ) micro-light-emitting diode (micro LED) devices without post-growth annealing were grown by metalorganic chemical vapor deposition (MOCVD). During the initial growth of the top n--GaN layer, the device forms island-like structures, allowing hydrogen to escape through the gaps between islands, thereby achieving activation of the p-GaN layer. The device achieves an operating voltage of 2.99 V at 20 A/cm2, a peak wall-plug efficiency (WPE) of 45.23%, and exhibits more uniform luminescence intensity in the electroluminescence (EL) image. This work establishes a pathway for enhancing the performance of an MOCVD-grown TJ.

The low modulation bandwidth of AlInGaP red micro light-emitting diodes (Micro-LEDs) limits full-color visible light communication (VLC) applications. Here, we demonstrate fast modulation speed long wavelength InGaN Micro-LEDs with red multiple quantum wells (MQWs) that exhibit sharp and uniform interfaces. The red Micro-LEDs show extremely low reverse leakage current of 1.77 & times; 10(-11) A at-5 V and an external quantum efficiency (EQE) of 4.07%. The-3 dB modulation bandwidth reaches 1.01 GHz for 20 mu m device, which is the highest one among red Micro-LEDs. The dependence of modulation bandwidth on current densities revealed the transition of carrier lifetime mechanisms with current injection level. Furthermore, an optical communication system was established, achieving open eye diagrams up to 1 Gbps with measured quality factors. These results demonstrate the large potential of long wavelength InGaN Micro-LEDs for next-generation highspeed VLC systems and optical computing.

Thermally activated delayed fluorescence (TADF) and the very recently established thermally stimulated delayed phosphorescence (TSDP) are two promising approaches for enhancing the performance of organic light-emitting devices (OLEDs). Here, we have developed a new class of through-space charge transfer (TSCT) carbazolylgold(III) C^C^N complexes with unique TADF-TSDP properties by introducing a rigid arylamine on the carbazolyl auxiliary ligand. The highly twisted conformation between the C^C^N and carbazolyl ligands induces strong through-bond ligand-to-ligand charge transfer (TB-LLCT) character in their lowest singlet and triplet excited states, with small singlet-triplet energy gaps for efficient TADF. Moreover, the close spatial proximity between the cyclometalating ligand and the lateral arylamine enables appreciable intramolecular through-space electronic coupling that allows the generation of relatively low-lying triplet through-space ligand-to-ligand charge transfer (3TS-LLCT) excited states. The TADF-TSDP properties are verified by temperature-dependent emission, lifetimes, and ultrafast transient absorption studies. Interestingly, through better alignment with extended planarity and the strengthening of the electron-donating ability of the lateral arylamine, the enhanced through-space electronic coupling can effectively perturb the energies of 3TBCT, 3TSCT, and intraligand (3IL) excited states and thus manipulates the TSDP efficiency. Orange-emitting vacuum-deposited OLEDs made with these gold(III) complexes demonstrate respectable maximum external quantum efficiencies of >10% and long operational half-lifetimes of up to 65,314 h at a luminance of 100 cd m-2. This work not only demonstrates the realization of interesting TADF-TSDP and TSCT properties in the gold(III) C^C^N cyclometalated system but also enriches the diversity of molecular design for high-performance TSDP and TSCT emitters.

We demonstrate ultra-high luminous efficacy InGaN-based green mini-light-emitting diodes (mini-LEDs) grown on c-plane patterned sapphire substrates using metal organic chemical vapor deposition (MOCVD). An Al-treatment technique was developed during multiple quantum wells (MQWs) growth. The Al-treatment InGaN green QWs show a significantly improvement in the radiative recombination efficiency and the Al-treatment 520 nm flip-chip InGaN green mini-LEDs show an ultra-high efficiency after package: a peak external quantum efficiency (EQE) of 65.0% and a peak wall-plug efficiency (WPE) of 60.1%, representing significant progress in addressing the “green gap” challenge.

Micro-light-emitting diodes (µLEDs) are gathering significant interest as a technology for emerging micro-displays. However, µLEDs encounter numerous obstacles, including size-dependent efficiency loss, poor efficiency of red µLEDs, and challenges associated with the mass transfer and integration of full-color µLEDs. These issues become more acute in ultra-small µLEDs (<5 µm), which were required by the augmented reality (AR) displays. Here, we discuss the principal challenges faced by µLEDs and explore the possible solutions. We highlight recent advances in InGaN-based RGB µLEDs tailored for AR displays. In particular, we discuss the advancements in ultra-small InGaN µLEDs scaled down to 1 µm, the developments in InGaN red µLEDs, and the implementation of tunnel junction-based cascaded InGaN µLEDs for monolithic integration.

Micro-light-emitting diodes (microLEDs) can improve existing displays and enable disruptive technologies like augmented reality (AR). However, ignoring smaller devices near 1 mu m overlooks (at least) two additional size-dependent effects that improve microLED efficiency: directionality and extraction efficiency increase as size decreases, and surface recombination is reduced as indium content increases (in InGaN microLEDs). This study shows that both combined effects counteract size-dependency efficiency droop, where the magnitude of positive effects increases with indium concentration (from blue to red) in InGaN. As the microLEDs' diameter reduced from 50 to 1 mu m, the external quantum efficiency (EQE) of 500 nm microLEDs fell from 16.5% to 14%, while the EQE of 600 nm devices increased from 2.7% to 7.1%. Although the efficiency of conventionally sized AlInGaP LEDs remains significantly higher than InGaN, the results of this study suggest that very high EQE of red microLED with sizes approaching 1 mu m can be realized using InGaN materials instead of AlInGaP. In addition to improving performance, consolidating to an entirely InGaN-based microLED display would reduce costs and streamline resources to help achieve AR and other next-generation displays.

The developments of high performance 1-10 micron size InGaN based RGB MicroLEDs are discussed. Through novel epitaxial growth and processing, and transparent packaging we have achieved external quantum efficiencies as high as 58% EQE at 450nm for microLEDs. The critical challenges of µLEDs, namely full-color scheme, decreasing pixel size and mass transfer technique, and their potential solutions are explored. Recently, we have demonstrated efficient microLEDs emitting in the blue to red at dimensions as small of 1 micron. Using strain relaxation methods we have also extending the wavelength range of the InGaN alloys as into the red with emission as long as 640nm. Red InGaN based red MicroLEDs with efficiencies of 6% has been fabricated, and they display superior temperature performance in comparison to AlGaInP based devices. This work was supported by the Solid State Lighting and Energy Electronics Center(SSLEEC) at UC Santa Barbara.

AlGaN-based UV-A LEDs have wide applications in medical treatment and chemical sensing; however, their efficiencies are still far behind visible LEDs or even shorter wavelengths UV-C counterparts because of the large lattice mismatch between the low-Al-content active region and the AlN substrate. In this report, we investigated the composition and thickness of the quantum barrier in the active region in terms of LED performance. Due to the improved strain management and better carrier confinement, efficient UV-A LEDs (320 nm - 330 nm) with EQEs up to 6.8% were demonstrated, among the highest efficiencies at this wavelength range.

We demonstrate a significant quantum efficiency enhancementofInGaN red micro-light-emitting diodes (mu LEDs). The peak externalquantum efficiency (EQE) of the packaged 80 x 80 mu m(2) InGaN red mu LEDs was largely increased to 6.0% at 12A/cm(2), representing the significant process in exploringthe efficiency of InGaN red mu LEDs. The improvement of the EQEis attributed to the significant enhancement of the quantum efficiency,which is confirmed by the electron-hole wavefunction overlapin the InGaN quantum well from the band gap simulation and the photoluminescenceintensity ratio at room temperature/low temperature. Ultrasmall 5x 5 mu m(2) InGaN red mu LEDs were also obtained,which show a high peak EQE of 4.5%. This work demonstrates a simpleapproach to achieving highly efficient InGaN red mu LEDs, whichare very promising candidates for ultrasmall red mu LEDs requiredby AR/VR displays.

We demonstrate vertical integration of nitride-based blue/green micro-light-emitting diodes (µLEDs) stacks with independent junctions control using hybrid tunnel junction (TJ). The hybrid TJ was gown by metal organic chemical vapor deposition (p + GaN) and molecular-beam epitaxy (n + GaN). Uniform blue, green and blue/green emission can be generated from different junction diodes. The peak external quantum efficiency (EQE) of the TJ blue µLEDs and green µLEDs with indium tin oxide contact is 30% and 12%, respectively. The carrier transportation between different junction diodes was discussed. This work suggests a promising approach for vertical µLEDs integration to enhance the output power of single LEDs chip and monolithic µLEDs with different emission colors with independent junction control.

We demonstrate high-performance 10 × 10 μ m 2 InGaN amber micro-size LEDs ( μ LEDs). At 15 A cm −2 , the InGaN μ LEDs show a single emission peak located at 601 nm. The peak external quantum efficiency (EQE) and wall-plug efficiency are 5.5% and 3.2%, respectively. Compared to the 100 × 100 μ m 2 μ LEDs, the 10 × 10 μ m 2 InGaN red μ LEDs maintain a similar EQE value with the same efficiency droop. These results point out that InGaN materials are much more promising for higher efficiency than the common AlInGaP materials for the ultra-small size red μ LEDs required by augmented reality and virtual reality displays.

We present efficient red InGaN 60 × 60 μm2 micro-light-emitting diodes (μLEDs) with an epitaxial tunnel junction (TJ) contact. The TJ was grown by metal-organic chemical vapor deposition using selective area growth. The red TJ μLEDs show a uniform electroluminescence. At a low current density of 1 A/cm2, the emission peak wavelength is 623 nm with a full-width half maximum of 47 nm. The peak external quantum efficiency (EQE) measured in an integrating sphere is as high as 4.5%. These results suggest a significant progress in exploring high efficiency InGaN red μLEDs using TJ technology.

Red micro-size light-emitting diodes (μLEDs) less than 10 × 10 μm2 are crucial for augmented reality (AR) and virtual reality (VR) applications. However, they remain very challenging since the common AlInGaP red μLEDs with such small size suffer from a dramatic reduction in the external quantum efficiency. In this work, we demonstrate ultra-small 5 × 5 μm2 607 nm amber μLEDs using InGaN materials, which show an EQE over 2% and an ultra-low reverse current of 10−9 A at −5 V. This demonstration suggests promising results of ultra-small InGaN μLEDs for AR and VR displays.

The developments of high performance InGaN based micro-light-emitting diodes (µLEDs) are discussed. Through novel epitaxial growth and processing, and transparent packaging we have achieved external quantum efficiencies as high as 58% EQE at 450nm for MmicroLEDs. The critical challenges of µLEDs, namely full-color scheme, decreasing pixel size and mass transfer technique, and their potential solutions are explored. Recently, we have demonstrated efficient microLEDs emitting in the blue to green at dimensions as small of 1 micron. Red InGaN based red MicroLEDs with efficiencies of 2.5% has also been fabricated.

InGaN-based red micro-size light-emitting diodes (μLEDs) have become very attractive. Compared to common AlInGaP-based red µLEDs, the external quantum efficiency (EQE) of InGaN red µLEDs has less influence from the size effect. Moreover, the InGaN red µLEDs exhibit a much more robust device performance even operating at a high temperature of up to 400 K. We review the progress of InGaN red μLEDs. Novel growth methods to relax the strain and increase the growth temperature of InGaN red quantum wells are discussed.

AlGaN-based deep ultraviolet (DUV) micro-light-emitting diodes (μLEDs) with emission wavelengths between 277 and 304 nm with mesa dimensions down to 20 μm were fabricated. Their size-dependent electrical and optical characteristics were analyzed. At 20 A cm−2, the external quantum efficiency (EQE) increased from 2.0% to 2.3% mainly due to the improved light extraction efficiency; the forward voltage was 7.6 V in 20 μm sized μLEDs in comparison to 9.1 V in 300 μm LEDs due to better current spreading in the smaller devices. The peak EQEs of the 20 μm μLEDs were 2.5% and 4.0% for 277 and 304 nm, among the highest reported for DUV μLEDs.

We demonstrate room-temperature stimulated emission at 568 nm from low dislocation density InGaN/GaN multi-quantum wells. For a 1.4 mm long and a 50 μm wide ridge bar optically pumped by a high-power pulsed laser, we observed an emission peak at 568 nm with a narrow spectral width of less than 2 nm at room temperature. The measured pumping threshold is less than 1.5 MW/cm2, and the polarization ratio of the emission is over 90%. This demonstration paves the way for the future development of electrically injected InGaN semiconductor yellow laser diodes.

AlGaN-based deep ultraviolet LEDs have attracted significant interest as a reliable and efficient disinfection technology to combat the pandemic outbreaks. However, EQEs of commercial DUV LEDs is currently low. One of the bottlenecks that limit the overall efficiency is the low light extraction efficiency (LEE), which is <15% for conventional flip chip devices. Many attempts have been made to increases the LEE, such as using thin (or no) absorbing p-GaN layer or fabricating novel microstructures, which often result in significant increase in the forward voltage or involve costly processing steps. $\mu\text{LEDs}$ have been proved to increase the LEE in visible wavelength devices but there are a few reports on the size dependence characteristics in the DUV range [1]–[2]. Additionally, $\mu\text{LEDs}$ can prevent the current crowding present in large UV LEDs since growing a thick and conductive n-AlGaN on AlN templates without relaxation remains a challenge.