Sidewall Defects Research Articles

Dimensional downscaling and quantum engineering: A path to high-performance micro-LEDs

The investigation of the optoelectronic performance of AlGaN-based ultraviolet-C (UV-C) micro light-emitting diodes (μLEDs) emitting at 273 nm is carried out numerically by reducing the chip area from large LED (300 × 300 μm2) to μLED (25 × 25 μm2). However, due to the high surface to volume ratio of μLED, surface recombination becomes dominant that is generated due to robust sidewall defects. The enhanced current spreading in μLED further affects the carrier injection in the active region as the electrons and holes are captured by sidewall defects. These effects are more dominant at low current density in μLED while at high current density, the sidewall defects get saturated, and the surface recombination weakens. Various optimization strategies, such as quantum wells (QWs) width, quantum barriers (QBs) width, and QW number are carried out to study the effect on the performance of 25 × 25 μm2 UV-C μLED. These optimization strategies at low current density (0.1 A/cm2) further improved the electrical/optical properties of AlGaN-based UV-C μLEDs.

Enhancing optical output power efficiency in nitride‐based green micro light‐emitting diodes by sidewall ion implantation

AbstractThough micro‐LED (light‐emitting diode) displays are considered the emerging display technology, the micron‐scale LED chip size encounters severe efficiency degradation that may impact the power budget of the displays. This work proposes an ion implantation method to deliberately create a high‐resistivity sidewall in the InGaN/GaN green LED. Our study demonstrates that ion implantation suppresses reverse leakage current due to the mitigation of sidewall defects. For an LED mesa size of 10 × 10 μm2, optical output power density is improved by 36.2% compared to the device without implantation. Compared to a larger 100 × 100 μm2 device without implantation, we achieve only 21.3% degradation of output power density under 10 A/cm2 injection for a 10 × 10 μm2 LED with implantation. In addition, the ion implantation method can lower the wavelength shift by reducing light emission from the region near the sidewall (where the amount of Indium [In] clustering differs from the mesa region). The results show promise in addressing the efficiency challenges of micro‐LED displays by selective ion implantation.

GaAs-based red micro-light-emitting diodes with an oxide perimeter region for improved external quantum efficiency

Red micro-light-emitting diodes (μ-LEDs) with AlGaInP/GaInP multiple quantum wells are fabricated with an oxide perimeter region to control the current injection path. When the values of the external quantum efficiency (EQE) of the 30 μm-size μ-LED with the oxide perimeter region are compared with those of the device without the oxide perimeter region, an improvement as high as 40% is observed at current densities <80 A/cm2. From the finite-difference time-domain simulation of the light-extraction efficiency (LEE), which shows that the LEE of the device with the oxide perimeter region is ∼12% smaller than that of the device without the oxide perimeter region, it can be seen that the increased EQE is attributed to the improvement of the internal quantum efficiency (IQE). Since the oxide perimeter region limits the current paths to the sidewalls of the μ-LED chips, the nonradiative recombination via sidewall defects is considered suppressed, resulting in the improvement of the IQE. The oxidation of the AlGaAs layer utilized in this work is easy to implement and accurately controllable, suitable for mass-production of high-efficiency red μ-LEDs for display applications.

Enhanced solar hydrogen evolution by laminated integration of n+p-SiIP/TiO2/Pt inverted pyramid black Si photocathode

The nano/microstructuring of silicon (Si) via chemical methods has garnered significant attention due to its excellent light-trapping capabilities across a wide spectral range. Current research has predominantly focused on the synthesis of pyramidal-shaped microtextures, which enable two reflections on the surface, while largely overlooking the superior light-trapping potential of inverted pyramid silicon (SiIP) microtextures, which theoretically allow for three reflections. Moreover, there has been limited investigation into the application of inverted pyramid black silicon for solar-driven hydrogen evolution. This study reports the synthesis of uniformly arranged inverted pyramid-textured black silicon using the copper-assisted chemical etching (Cu-ACE) method to enhance the efficiency of solar-driven water splitting for hydrogen production. The formation mechanism and the influence of copper-localized surface plasmon resonance (Cu-LSPR) from Cu nanoparticle (NP) byproducts on photoelectrochemical (PEC) activity were systematically analyzed. To reduce sidewall defects and minimize photogenerated carrier recombination, the surface of the SiIP was treated with tetramethylammonium hydroxide (TMAH). A vertical PN junction was developed through ion implantation to reduce the external bias of the SiIP. Additionally, a uniform TiO₂ antireflective layer was deposited via atomic layer deposition (ALD), reducing the average reflectance of the SiIP-T4 to 5.78 % over the 300–1100 nm wavelength range. MoSₓ and Pt NPs were electrodeposited to improve the fill factor and enhance HER kinetics. With optimized catalyst loading, the n+p-SiIP-T4/TiO₂/Pt 80 mC electrode achieved a photocurrent density of 8.0 mA cm−2 at 0 V vs. RHE, an applied bias photon-to-current efficiency (ABPE) of 0.93 % at 0.24 V vs. RHE, and a double-layer capacitance (Cdl) of 91 μF cm−2. The onset potential (Von) was positively shifted by ∼1.13 V to 0.49 V vs. RHE compared to a SiIP photocathode, and the photocathode operated continuously at 0 V vs. RHE for 27 h in an acidic electrolyte. These results demonstrate that SiIP has significant potential for PEC hydrogen evolution, with further performance optimization achievable through structural and surface engineering.

Size and temperature effects on optoelectronic properties of Micro-LED arrays for display applications

In recent years, Micro-light-emitting diode (Micro-LED) has attracted much attention in the display field, because it provides the possibility of high pixel density, etc. The implementation of high pixel density is accompanied by the reduction of size, during which the performance degradation caused by sidewall defects gradually increases. At the same time, the increase in power density and difficulty in heat dissipation caused by high pixel density can also lead to poor thermal management, resulting in an increase in junction temperature, thus affecting the display effect. In this paper, we prepared seven different sizes of Micro-LED and studied the influence of size and temperature effects on the optoelectronic properties. Smaller-sized Micro-LED could withstand higher current densities because it was not affected by the current crowding effect. However, it tends to have a larger series resistance (RS) and a lower external quantum efficiency (EQE) due to sidewall defects created during etching. The luminance of the 100 μm and 7 μm Micro-LED was 340000 cd/m2 (at 83 A/cm2) and 32000 cd/m2 (at 773 A/cm2), respectively. The peak EQE of 100 μm Micro-LED was 16.87 %. On this basis, the temperature-dependence of the optoelectronic properties of 10 μm and 50 μm Micro-LED were studied. The larger the size of Micro-LED, the better the operational stability it exhibited. From the room temperature (RT) rose to 100 ℃, the EQE of the 10 μm and 50 μm Micro-LED decreased by 16 % and 13.1 %, respectively. These experimental results provide important data for the design and preparation of Micro-LED of different sizes and for exploring the operational stability at high temperatures.

External quantum efficiency enhancement of GaN-based blue LEDs by treating their full-M-sided hexagonal mesa with TMAH solution.

In recent years, III-Nitride-based micro light-emitting diodes (micro-LEDs) have emerged in many fields and gained more attention. However, fabricating high-efficiency micro-LEDs still remains a challenge due to the presence of sidewall damage. In this study, a GaN-based single blue micro-LED with a full-M-sided hexagonal mesa was prepared. The mesa has a circumradius of 10 µm and was treated with a tetramethylammonium hydroxide (TMAH) solution. Experimental results show that the sidewall defects introduced by dry etching damage act as non-radiative recombination centers and greatly impair the performance of the device. By constructing a full-M-sided hexagonal structure and soaking in a TMAH solution, the etching damage on the sidewall can be eliminated to the greatest extent, thereby reducing sidewall defects. In consequence, the peak EQE of the devices treated with the TMAH solution exceeded 10% at low current density, an increase of 9% compared with the untreated samples. This work provides, to our knowledge, a new approach to improving the efficiency of GaN-based micro-LEDs.

Reconstruction of Medially Based Nasal Ala and Sidewall Defect, Spanning the Alar Groove.

Reconstruction of Medially Based Nasal Ala and Sidewall Defect, Spanning the Alar Groove.

Numerical analysis of the influence of sidewall defects on AlGaN-based deep ultraviolet micro-light emitting diodes

The optoelectronic performance of AlGaN-based deep ultraviolet micro-light emitting diodes are strongly affected by surface recombination at the mesa sidewall. Herein, the influence of sidewall defect density and location changes on the photoelectric properties and carrier recombination mechanisms were theoretically investigated. The results indicate a significant deterioration in the internal quantum efficiency and optical power with an increase in the sidewall defect density at the edge of the LED mesa. This deterioration is attributed to the Shockley-Read-Hall nonradiative recombination caused by sidewall defects. The sidewall defects also act as traps for electrons and holes, significantly affecting the carrier injection capability. Furthermore, the position dependence of carrier concentration and recombination rate along the lateral dimension of the LED mesa were studied. The results show that etching process not only causes sidewall damage but can damage the quality of internal epitaxial materials. These effects should be minimized by optimizing the dry-etching process.

Comparative analysis of microstructure, electrical and optical performance in sidewall etching process for GaN-based green micro-LED

Micro-LEDs show the size-dependent external quantum efficiency (EQE) reduction problem, mainly owing to increased non-radiative recombination loss at the sidewall for smaller chip size. In this work, the evolution of microstructure, surface potential and optical performance of the green micro-LED sidewall was investigated comparatively after inductively coupled plasma (ICP) and tetramethylammonium hydroxide (TMAH) etching through transmission electron microscopy (TEM), Kelvin probe force microscope (KPFM), cathodoluminescence (CL) and time-resolved photoluminescence (TRPL). As confirmed by TEM and geometric phase analysis (GPA), ICP etching causes sidewalls to form atomically rough semi-polar surfaces and increases 25% compressive strain at the sidewall compared to the inside. TMAH solution introduces new sidewall defects due to excessive etching of three atomic layers of InGaN. Holes accumulate at the surface because of build-in electric field as showed by KPFM. The sidewall defects lead to a decrease in carrier lifetime resulting in uneven luminescence of micro-LED mesa. TMAH treatment removes the damaged layer and reduces the non-radiative recombination rate. ICP causes damage to the nanoscale structure, however the influence of sidewall defects on the carrier behavior is in the micron range due to unavoidable surface dangling bonds and surface lattice relaxation. A non-radiative recombination mechanism is proposed based on strain relaxation.

Multi-Subunit Repair With the Nasolabial Burow's Advancement Flap.

We will describe the use of nasolabial Burow's advancement flaps (perialar crescentic advancements) to repair multi subunit defects of the nasal sidewall including the adjacent cheek, dorsum, tip, and ala without the need of additional flaps. This retrospective single centre study analyzed 6 month postoperative photographs using the Manchester Scar scale. The operative technique is described in detail. Of 355 cases, 336 were available for analysis. The median Manchester Scar scale was 7 for both sidewall defects and multi-subunit defects. There were low rates of infection or necrosis. With the correct technique, the nasolabial Burow's advancement alone is suitable to repair even large multi-subunit defects involving the nasal sidewall, cheek, dorsum, tip, and ala with high-level aesthetic and functional results.

GaN/InGaN LED Sidewall Defects Analysis by Cathodoluminescence and Photosensitive Kelvin Probe Force Microscopy

GaN/InGaN LED Sidewall Defects Analysis by Cathodoluminescence and Photosensitive Kelvin Probe Force Microscopy

ROS-responsive sprayable hydrogel as ROS scavenger and GATA6+ macrophages trap for the prevention of postoperative abdominal adhesions

Postoperative abdominal adhesions are a common clinical problem after surgery and can cause many serious complications. Current most commonly used antiadhesion products are less effective due to their short residence time and focus primary on barrier function. Herein, we developed a sprayable hydrogel barrier (sHA-ADH/OHA-E) with self-regulated drug release based on ROS levels at the trauma site, to serve as a smart inflammatory microenvironment modulator and GATA6+ macrophages trap for non-adherent recovery from abdominal surgery. Sulfonated hyaluronic acid (HA) conjugates modified with adipic dihydrazide (sHA-ADH), and oxidized HA conjugates grafted with epigallocatechin-3-gallate (EGCG) via ROS-cleavable boronate bonds (OHA-E) were synthesized. sHA-ADH/OHA-E hydrogel was facilely fabricated within 5 s after simply mixing sHA-ADH and OHA-E through forming dynamic covalent acylhydrazones. With good biocompatibility, appropriate mechanical strength, tunable shear-thinning, self-healing, asymmetric adhesion, and reasonable in vivo retention time, sHA-ADH/OHA-E hydrogel meets the requirements of a perfect physical barrier. Intriguingly, sulfonic acid groups endowed the hydrogel with satisfactory anti-fibroblast and macrophage attachment capability, and were demonstrated for the first time to act as polyanion traps to prevent GATA6+ macrophages aggregation. Importantly, EGCG could be intelligently released by ROS triggering to alleviate oxidative stress and promote proinflammatory M1 macrophage polarize to antiinflammatory M2 phenotype. Further, the fibrinolytic system balance was restored to reduce fibrosis. Thanks to the above advantages, the sHA-ADH/OHA-E hydrogel exhibited excellent anti-adhesion effects in a rat sidewall defect–cecum abrasion model and is expected to be a promising and clinically translatable antiadhesion barrier.

Performance comparison of InGaN-based 40–80 μm micro-LEDs fabricated with and without plasma etching

The fabrication of InGaN-based blue 4✕4 array micro-LEDs (μLEDs) with 40 μm ✕40 μm chip size and 2✕2 array μLEDs with 80 μm ✕80 μm chip size etching by the inductive coupled plasma reactive ion etching (ICPRIE) and defect-free neutral beam etching (NBE) processes was studied in this work. In μLEDs of this size, the influence of defects formation in the sidewalls on EQE was evaluated. There was almost no difference in EQE between μLEDs array etched by the NBE process no matter 40 μm ✕40 μm and 80 μm ✕80 μm, but the dependence was observed in the ICPRIE. Even with this size, it was found that the size effect of EQE is smaller than that in case of using ICPRIE for defect-free neutral beam etching. This impact is substantial since μLED predominantly operated at low current density, around 1–5 A/cm2. Consequently, the reduction of defect density, encompassing both internal and sidewall defects, becomes imperative even in 40–80 μm InGaN-based μLEDs. This not only improves the overall efficiency of μLEDs but also fortifies the brightness stability of μLED displays if process etching by NBE. It was also found that the etching shape had an influence on EQE. It could be attributed to fact that the etching profile angle of NBE was more vertical than that of ICPRIE. Because the different angles of the mesa resulted in different light intensity. The μLEDs emitting with a wavelength of 450 nm, the light extraction efficiency and intensity at a mesa angle 58° of NBE etching μLEDs was about 8% lower than those of an angle (38°) of ICPRIE etching μLEDs by simulation.

Influence of Shape and Size on GaN/InGaN μLED Light Emission: A Competition between Sidewall Defects and Light Extraction Efficiency

Influence of Shape and Size on GaN/InGaN μLED Light Emission: A Competition between Sidewall Defects and Light Extraction Efficiency

Analysis of size-dependent optoelectronic properties of red AlGaInP micro-LEDs.

We have theoretically investigated the size-dependent optoelectronic properties of InGaP/AlGaInP-based red micro-LEDs through an electro-optical-thermal coupling model. The model considers thermal effects due to current crowding near the electrodes, non-thermal efficiency droop due to electron leakage, and etch defects on the LED sidewall. Sidewall defects reduce the carrier concentration at the light-emitting surface's edge and exacerbate the current crowding effect. In addition, p-side electron leakage at high current densities is the leading cause of the efficiency droop of AlGaInP LEDs. In contrast, the effect of temperature on the overall efficiency degradation of LEDs is even more significant.

Size-dependent sidewall defect effect of GaN blue micro-LEDs by photoluminescence and fluorescence lifetime imaging.

Sidewall defects play a key role in determining the efficiency of GaN-based micro-light emitting diodes (LEDs) for next generation display applications, but there still lacks direct observation of defects-related recombination at the affected area. In this Letter, we proposed a direct technique to investigate the recombination mechanism and size effect of sidewall defects for GaN blue micro-LEDs. The results show that mesa etching will produce stress release near the sidewall, which can reduce the quantum confinement Stark effect (QCSE) to improve the radiative recombination. Meanwhile, the defect-related non-radiative recombination generated by the sidewall defects plays a leading role under low-power injection. In addition, the effective area of the mesas affected by the sidewall defects can be directly observed according to the fluorescence lifetime imaging microscope (FLIM) characterization. For example, the effective area of the mesa with 80 µm is affected by 23% while the entire area of the mesa with 10 µm is almost all affected. This study provides guidance for the analysis and repair of sidewall defects to improve the quantum efficiency of micro-LEDs display at low current density.

(Invited) Electroluminescence from Single-Walled Carbon Nanotubes with Quantum Defects

Individual single-walled carbon nanotubes with covalent sidewall defects have emerged as a new class of photon sources whose photoluminescence spectra can be tailored by the carbon nanotube chirality and the attached functional group/molecule. Here we present electroluminescence spectroscopy data from single-tube devices based on (7,5) carbon nanotubes, functionalized with dichlorobenzene molecules, and wired to graphene electrodes. We observe electrically generated, defect-induced emissions that are controllable by electrostatic gating and strongly red-shifted compared to emissions from pristine nanotubes. The defect-induced emissions are assigned to excitonic and trionic recombination processes by correlating electroluminescence excitation maps with electrical transport and photoluminescence data. At cryogenic conditions additional, gate-dependent emission lines appear which are assigned to phonon-assisted hot-exciton electroluminescence from quasi-levels. Similar results were obtained with functionalized (6,5) nanotubes. We also compare functionalized (7,5) electroluminescence data with photoluminescence of pristine and functionalized (7,5) nanotubes redox-doped using gold(III) chloride solution. This work shows that electroluminescence excitation is selective toward neutral defect-state configurations with the lowest transition energy, which in combination with gate-control over neutral versus charged defect-state emission leads to high spectral purity.Reference: Min-Ken Li et al., ACS Nano 2022 (doi: 10.1021/acsnano.2c03083) Figure 1

Reconstruction of medium and large nasal defects.

Objective: The aim of this study is to share our experience with nasal reconstruction and to give a standardized algorithm for nasal reconstruction. Study Design: Descriptive cross sectional. Setting: Burns and Plastic Surgery Center, Peshawar. Period: January 2019 to December 2022. Material & Methods: Data was obtained from patient records after approval from IREB. Patients with multiple co-morbidities and small defects (<1.5cm) were excluded from this study. Defects were classified based on anatomic areas of radix, dorsum, sidewall, alar and lower third nasal defects. Cases were cross tabulated regarding site for the reconstructive options to generate the treatment algorithm. Results: A total of 51 cases were included in the study including 30 (58.8%) male patients. Mean age of patients was 48.12+21.89SD. Skin malignancies were the most common (n=35, 68.6%). Nasal ala was the most common site reconstructed in our study (25.5%) followed by nasal dorsum and sidewalls. Medium size (41.2%) was the most common. In 64.8% (n=33) cases, forehead based flaps were used to reconstruct the nasal defects (Table-I). In 5.9% cases we observed flap congestion. In 19 (37.25%) cases, patients presented with additional soft tissue defects which needed reconstruction (Table-II). Reconstructive options are presented as an algorithm based on the defect site (Figure-1). Conclusion: In this study we shared our experience with the readers regarding reconstruction of the nasal detects. We have formulated an algorithm for reconstruction of these defects that will simplify reconstruction in such cases.

P‐64: Investigation of Fabrication Technologies of GaN‐based Micro‐LED Devices

Micro‐light‐emitting diode (Micro‐LED) is a new type of display device based on the third‐generation semiconductor gallium nitride (GaN) material. Micro‐LED has been applied to micro‐display technology due to its huge development potential. However, the EQE of Micro‐LEDs decreases with the decrease of the sidewall defects, and the passivation process can reduce the sidewall damage and improve the EQE. In this study, the fabrication technology of Micro‐LEDs was summarized and InGaN/GaN multi‐quantum wells (MQWs) Micro‐LEDs from 10 × 10 μm to 200 × 200 μm were fabricated. The improvement effect of different passivation materials on the electrical characteristics of Micro‐LEDs was explored. The results showed that passivation materials could effectively reduce the leakage of the device, reduce the sidewall damage and reduce the ideal factor, among which Si 3N 4 had the most obvious effect.

Performance improvement of GaN-based microdisk lasers by using a PEALD-SiO2 passivation layer.

Dry-etching is often utilized to shape GaN-based materials. However, it inevitably causes plenty of sidewall defects as non-radiative recombination centers and charge traps that deteriorate GaN-based device performance. In this study, the effects of dielectric films deposited by plasma-enhanced atomic layer deposition (PEALD) and plasma-enhanced chemical vapor deposition (PECVD) on GaN-based microdisk laser performance were both investigated. The results demonstrated that the PEALD-SiO2 passivation layer largely reduced the trap-state density and increased the non-radiative recombination lifetime, thus leading to the significantly decreased threshold current, notably enhanced luminescence efficiency and smaller size dependence of GaN-based microdisk lasers as compared with the PECVD-Si3N4 passivation layer.