Vertical-structure Light-emitting Diodes Research Articles

Self-Assembled Size-Tunable Microlight-Emitting Diodes Using Multiple Sapphire Nanomembranes.

Microlight-emitting diode (Micro-LED) is the only display production technology capable of meeting the high-performance requirements of future screens. However, it has significant obstacles in commercialization due to etching loss and efficiency reduction caused by the singulation process, in addition to expensive costs and a significant amount of time spent on transfer. Herein, multiple-sapphire nanomembrane (MSNM) technology has been developed that enables the rapid transfer of arrays while producing micro-LEDs without the need for any singulation procedure. Individual micro-LEDs of tens of μm size were formed by the pendeo-epitaxy and coalescence of GaN grown on 2 μm width SNMs spaced with regular intervals. We have successfully fabricated micro-LEDs of different sizes including 20 × 20 μm2, 40 × 40 μm2, and 100 × 100 μm2, utilizing the membrane design. It was confirmed that the 100 × 100 μm2 micro-LED manufactured with MSNM technology not only relieved stress by 80.6% but also reduced threading dislocation density by 58.7% compared to the reference sample. It was proven that micro-LED arrays of varied chip sizes using MSNM were all transferred to the backplane. A vertical structure LED device could be fabricated using a 100 × 100 μm2 micro-LED chip, and it was confirmed to have a low operation voltage. Our work suggests that the development of the MSNM technology is promising for the commercialization of micro-LED technology.

Ultrathin LED technology helps advance 6G

An approach using subwavelength vertical-structure LEDs provides a key step towards visible light communication.

Light-responsive vertical-structure light-emitting diode

Vertical-structure light-emitting diodes (VSLEDs) are promising candidates for visible light communication, high-power solid-state lighting and display. Here, we propose, fabricate and characterize light-responsive VSLEDs, which are implemented on a 2-inch metal-based bonded III-nitride-on-silicon wafer. Thick epitaxial films are thinned without hard mask to reduce the number of confined optical modes, enhancing the light extraction efficiency. Owing to the overlap between its emission and detection spectra, the VSLEDs exhibit light-responsive light-emitting phenomenon and experimentally demonstrate full-duplex light communication, opening promising approaches toward a variety of novel internet of things applications.

Rectification behavior of polarization effect induced type-II n-GaN/n-type β-Ga2O3 isotype heterojunction grown by metal organic vapor phase epitaxy

We demonstrated the growth of high-quality and compressive-stressed single-crystal c-GaN on (2¯01) β-Ga2O3 utilizing metal organic vapor phase epitaxy. Rectification behavior of the n-GaN/n-Ga2O3 isotype heterojunction was observed. Valence and conduction band offsets were determined to be 1.625 eV ± 0.07 eV and –0.165 eV ± 0.07 eV, respectively, confirming a type-II heterojunction due to the polarization effect. The extracted forward (0.702 V) and reverse (0.178 V) turn-on voltages could be ascribed to the band bending (0.695 eV) effect and the conduction band offset, respectively. The present work may lead to a deeper understanding of the GaN/β-Ga2O3 heterojunction and play a guiding role in the development of the GaN-based vertical structure light-emitting diodes on β-Ga2O3.

自分裂GaN基垂直结构LED研究

自分裂GaN基垂直结构LED研究

自分裂GaN基垂直结构LED研究

自分裂GaN基垂直结构LED研究

Epitaxy of III-Nitrides on β-Ga2O3 and Its Vertical Structure LEDs

β-Ga2O3, characterized with high n-type conductivity, little lattice mismatch with III-Nitrides, high transparency (>80%) in blue, and UVA (400–320 nm) as well as UVB (320–280 nm) regions, has great potential as the substrate for vertical structure blue and especially ultra violet LEDs (light emitting diodes). Large efforts have been made to improve the quality of III-Nitrides epilayers on β-Ga2O3. Furthermore, the fabrication of vertical blue LEDs has been preliminarily realized with the best result that output power reaches to 4.82 W (under a current of 10 A) and internal quantum efficiency (IQE) exceeds 78% by different groups, respectively, while there is nearly no demonstration of UV-LEDs on β-Ga2O3. In this review, with the perspective from materials to devices, we first describe the basic properties, growth method, as well as doping of β-Ga2O3, then introduce in detail the progress in growth of GaN on (1 0 0) and (−2 0 1) β-Ga2O3, followed by the epitaxy of AlGaN on gallium oxide. Finally, the advances in fabrication and performance of vertical structure LED (VLED) are presented.

Efficiency improved by monolithic integration of HEMT with vertical-structure LEDs and Mg doping on dry etched GaN

Efficiency is essential to an integrated lighting system. In this work, monolithic integration of AlGaN/GaN high electron mobility transistors (HEMTs) with vertical-structure InGaN/GaN light emitting diodes (LEDs) was studied.

Pharmacokinetics and tissue distribution of RVT-801, a recombinant human acid ceramidase, at efficacious doses in a murine model of Farber disease

We investigate the effect of trench etching and arrayed p-electrodes in improving current spreading and the efficiency of light extraction of GaN-based vertical-structured light-emitting diodes (VLEDs). Both simulated and experimental results on the uniformities of current distribution and light emission are presented and discussed. For a 2 × 2 array VLED with a die size of 1020 × 1020 μm2, enhancements in light output power by 0.38% (6.03%) and wall-plug efficiency by 2.79% (2.32%) at 364.4 mA/mm2 (728.9 mA/mm2) as compared with that of regular VLED are achieved experimentally, which are attributed to improved current spreading from the arrayed p-electrode and trench designs as well as enhanced light emission from the trench region.

GaN基垂直结构LED的n型电极结构设计及芯片制备

GaN基垂直结构LED的n型电极结构设计及芯片制备

基于谐振腔效应的近紫外垂直结构LED光萃取效率优化

基于谐振腔效应的近紫外垂直结构LED光萃取效率优化

Enhanced Light Output of UVA GaN Vertical LEDs With Novel DBR Mirrors

The emission efficiency of GaN-based light-emitting diodes (LEDs) decreases significantly as the emission wavelength is shorter than 370 nm because of the absorption of emission light in the GaN layers. The vertical LED structure could be applied to avoid the absorption problem, because the undoped GaN layer would be removed and the n-GaN layer could be thinned as much as possible in the fabrication process. In this report, we propose a novel ultraviolet (UV) LED structure with a thin indium–tin–oxide (ITO) layer as the ohmic contact and a dielectric distributed Bragg reflector (DBR) as the high reflectivity mirror. Comparing referenced vertical UV LED structures with ITO/Ag as the metal mirror, the vertical UV LED with the ITO/DBR mirror shows the output power of approximately 190 mW at 350 mA with 7.9% enhancement.

An explanation for catastrophic failures of GaN-based vertical structure LEDs subjected to thermoelectric stressing

Both accelerated life tests and engineering practices present a common behavior: LED products may encounter catastrophic failure under thermo-electric co-stressing. The present work proposes that the applied thermoelectric stresses themselves are not necessary conditions but pre-conditions for LED breakdown. The deformation and sliding of the metal lines on n-GaN under thermoelectric co-stressing cause electrodes to become dilapidated. Such dilapidated electrodes with rough edges will help to generate localized high electrical fields. The catastrophic failure occurs during the de-trapping process of space charges in and around threading dislocations when the applied electric field is removed and short circuits form between the charged dislocation cores and the tips of the dilapidated electrodes. A phenomenological relationship is given to describe the interactions between temperatures and applied electric currents on the diffusion-flux-accommodated sliding and deformation of patterned metal electrodes on vertical LEDs. Such a law is coincident with the practical trend of LED failure rates observed in accelerated life tests and engineering applications.

Designing InGaN/GaN nano‐LED arrays for étendue‐limited applications

AbstractThis paper presents the far field results of a study by simulation using the finite‐difference time‐domain (FDTD) method of vertical light emitting diode structures with an incorporated ordered nanorod array in place of the typical surface roughened region. For a dipole placed directly below the centre nanorod in the FDTD model, highly collimated light is achieved by changing the radii of the nanorods, for a fixed array pitch, which we attribute mainly to Bragg diffraction. By changing the pitch only, higher diffraction orders are observed in the far field emission as the pitch is increased and a relative increase in the directionality of emission is predicted. (© 2015 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

基于混合型量子阱的GaN基垂直结构发光二极管性能

In order to solve the problem that Ga N-based vertical structure LEDs( VS-LEDs) suffer from efficiency droop under high current injection level,hybrid quantum wells( HQWs) with coupled quantum wells( CQWs) and normal quantum wells( NQWs) were employed. Compared to VSLEDs with NQWs,VS-LEDs with HQWs had better properties,wherein forward voltage reduced by0. 68 V and light-output power increased by 53. 0% at a forward current of 350 m A. Meanwhile,the relative external quantum efficiencies of VS-LEDs with NQWs and VS-LEDs with HQWs reduced to37. 7% and 67. 5% of their maximum,respectively. The results reveal that the efficiency droop of LEDs can become less severe by exploiting HQWs.

GaN-based substrates and optoelectronic materials and devices

In order to solve the problems of GaN heteroepitaxy on sapphire substrate, some techniques were explored. Freestanding GaN substrates have been made by hydride vapor phase epitaxy (HVPE), laser lift-off (LLO), and chemical mechanical polishing techniques. Wafer bending and cracking in the HVPE growth were partly settled by pulsed flow modulation method. High-crystal quality was established for 1.2 mm thick GaN substrate by X-ray diffraction measurement, in which the full width of half maximum values were 72, 110 arcsec for (102), (002) peaks. A novel micro-size patterned sapphire substrate (PSS) and a nano PSS were also fabricated. High-power vertical structure light emitting diodes (VSLEDs) have been developed by Au–Sn eutectic wafer bonding, homemade micro-area LLO, and light extraction structure preparation. The high-injection-level active region with low temperature GaN sandwiched layers was used for low-efficiency droop. The light output power of VSLED was achieved as 400 mW driven at 350 mA, and the dominant wavelength is about 460 nm. The structures and properties of strain modulated superlattices (SLs) and quantum wells as well as advanced simulation of carriers transport across the electron blocking layer were investigated in laser diodes. The hole concentration was achieved as high as 1.6 × 1018 cm−3 in AlGaN/GaN SLs:Mg by inserting an AlN layer. High-quality AlGaN epilayers and structures were grown by MOCVD. Some device structures of UV LEDs and detectors were demonstrated. The emission wavelength of 262 nm UV LED has been successfully fabricated. At last, high-quality InN and InGaN materials for solar cell were grown by boundary-temperature-controlled epitaxy and growth-temperature-controlled epitaxy. Hall-effect measurement showed a recorded electron mobility of 3,280 cm2/(V s) and a residual electron concentration of 1.47 × 1017 cm−3 at 300 K.

Enhanced light extraction in n-GaN-based light-emitting diodes with three-dimensional semi-spherical structure

Three-dimensional (3D) periodic micro/nanostructures can have a remarkable enhancement effect on light-emitting diodes (LEDs). However, simple, high-throughput and large-area fabrication of 3D periodic micro/nanostructures with a high duty ratio is difficult. In this Letter, high-duty-ratio 3D semi-spherical structures were fabricated on the surface of n-GaN-based vertical-structure LEDs by under-exposure ultraviolet lithography and dry etching. The resulting LEDs provide about 200% more light output power than those with a flat surface. This method of fabricating high-duty-ratio 3D semi-spherical structures could be used in other optical devices and shows potential for industrial production and commercialization.

Performance of GaN-based light-emitting diodes fabricated using GaN epilayers grown on silicon substrates.

Light extraction of GaN-based light-emitting diodes grown on Si(111) substrate (GaN-on-Si based LEDs) is presented in this study. Three different designs of GaN-on-Si based LEDs with the lateral structure, lateral structure on mirror/Si(100) substrate, and vertical structure on mirror/Si(100) substrate were epitaxially grown by metalorganic chemical vapor deposition and fabricated using chemical lift-off and double-transfer techniques. Current-voltage, light output power, far-field radiation patterns, and electroluminescence characteristics of these three LEDs were discussed. At an injection current of 700 mA, the output powers of LEDs with the lateral structure on mirror/Si(100) substrate and vertical structure on mirror/Si(100) substrate were measured to be 155.07 and 261.07 mW, respectively. The output powers of these two LEDs had 70.63% and 187.26% enhancement compared to that of LED with the lateral structure, respectively. The result indicated this vertical structure LED was useful in improving the light extraction due to an enhancement in light scattering efficiency while the high-reflection mirror and diffuse surfaces were employed.

High-Efficiency GaN-Based Vertical Light-Emitting Diodes with Periodic Beveled Rod-Shaped Structures

The periodic beveled micro-rods (BMRs) were constructed on the emission surface of GaN-based vertical light-emitting diodes (VLEDs) in order to improve the light-extraction efficiency. It was experimentally demonstrated that the light output power of the VLEDs with a periodic BMR (BMR-VLED) were enhanced about 15.6%, compared with that of the VLEDs with randomly textured surface (RT-VLED) at an injection current of 350 mA. This finding indicates that the photons emitted from the active layer were well out-coupled at an n-GaN surface having a periodic BMR structure, resulting in an increase in the probability of escaping from the VLED structure.

Partially sandwiched graphene as transparent conductive layer for InGaN-based vertical light emitting diodes

InGaN-based vertical structure light emitting diodes (VLEDs) with multi-layer graphene transparent electrodes with higher optical output have been fabricated and tested. High temperature annealing introduced inter-diffusion of metal atoms and Ga atoms and generated the partially sandwiched graphene structure, which contributed to the performance improvement of VLEDs.