Sidewall Defects Research Articles

P‐10.7: 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 side wall 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 Si3N4 had the most obvious effect.

Improved electrical properties of micro light-emitting diode displays by ion implantation technology

Generally, the inductively coupled plasma-reactive ion etching (ICP-RIE) mesa technology was used to remove p-GaN/MQWs and expose n-GaN for electrical contact in a fabricated micro light-emitting diode (μLED). In this process, the exposed sidewalls were significantly damaged which result in small-sized μLED presenting a strong size-dependent influence. Lower emission intensity was observed in the μLED chip, which can be attributed to the effect of sidewall defect during etch processing. To reduce the non-radiative recombination, the ion implantation using an As+ source to substitute the ICP-RIE mesa process was introduced in this study. The ion implantation technology was used to isolate each chip to achieve the mesa process in the μLED fabrication. Finally, the As+ implant energy was optimized at 40 keV, which exhibited excellent current–voltage characteristics, including low forward voltage (3.2 V @1 mA) and low leakage current (10–9 A@− 5 V) of InGaN blue μLEDs. The gradual multi-energy implantation process from 10 to 40 keV can further improve the electrical properties (3.1 V @1 mA) of μLEDs, and the leakage current was also maintained at 10–9 A@− 5 V.

Systematic study on size and temporal dependence of micro-LED arrays for display applications

Micro-LEDs are one of the most promising candidates for next-generation displays, yet they are inconvenienced by the efficiency reduction induced by the sidewall defects when pursuing further scaled-down device dimensions. We have systematically investigated both the size and temporal dependence of micro-LEDs. Micro-LED arrays with a mesa size ranging from 7 to 100 μm were prepared for display purposes. The luminance and external quantum efficiency (EQE) were measured and discussed. Surprisingly, micro-LED arrays with a smaller mesa size exhibit a higher EQE under 100 ns pulse duration operation when compared with longer pulse duration operations. Under certain short-pulsed excitation, a 7×7 μm2 micro-LED array even exhibits a >20% higher EQE as compared to the direct current (DC) or the long duration pulse operation condition. We thus concluded that the notorious efficiency reduction induced by sidewall defects in small-sized micro-LED arrays could be significantly reduced by applying short-pulse voltages.

Application of SCF-LTDP technology for a-Si:H film defective passivation in X-ray PIN-based photosensor

The quality and stability of X-ray flat panel detectors and fingerprint identifiers are crucial requirements for high-resolution applications and to ensure successful manufacture and commercially applicability. To achieve higher resolutions, the areas of the photodiodes must be reduced, which results in an increase in the leakage current owing to sidewall defects caused by the photodiodes. This study introduces a supercritical fluid low-temperature defect passivation (SCF-LTDP) treatment to repair the dangling bonds of amorphous silicon (a-Si) PIN-diode-based photo sensors. Unlike traditional atmospheric annealing processes, the hydrogen achieves a low-temperature and high-pressure fluid state in this technique, which offers the advantages of deeper penetration, higher surface tension, and greater viscous force. This technique helps suppress the leakage current generated in the reverse bias voltage by passivating the defects under illumination. The recombination current caused by the defects is, therefore, reduced, resulting in an overall increase of the photocurrent in the X-ray photodiode. The results obtained in this study are beneficial for the development of PIN diodes for panel detector applications.

29 GHz single-mode vertical-cavity surface-emitting lasers passivated by atomic layer deposition.

The fabrication processes of high-speed oxide-confined single-mode (SM)-vertical-cavity surface-emitting lasers (VCSELs) are complex, costly, and often held back by reliability and yield issues, which substantially set back the high-volume processing and mass commercialization of SM-VCSELs in datacom or other applications. In this article, we report the effects of Al2O3 passivation films deposited by atomic layer deposition (ALD) on the mesa sidewalls of high-speed 850-nm SM-VCSELs. The ALD-deposited film alleviates the trapping of carriers by sidewall defects and is an effective way to improve the performance of SM-VCSELs. The ALD-passivated SM-VCSELs showed statistically significant static performance improvements and reached a believed to be record-breaking SM-modulation bandwidth of 29.1 GHz. We also propose an improved microwave small-signal equivalent circuit model for SM-VCSELs that accounts for the losses attributed to the mesa sidewalls. These findings demonstrate that ALD passivation can mitigate processing-induced surface damage, enhance the performance of SM-VCSELs, and enable mass production of high-quality SM-VCSELs for mid- to long-reach optical interconnects.

Luminescence efficiency improvement of small-size micro light-emitting diodes by a digital etching technology.

The decrease of light output efficiency with the reduction of LED (light-emitting diode) die size is one of the challenges of micro-LED displays. Here we propose a digital etching technology that employs multi-step etching and treatment to mitigate sidewall defects exposed after mesa dry etching. In this study, by two-step etching and N2 treatment, the electrical properties of the diodes show an increase of forward current and a decrease in reverse leakage due to suppressed sidewall defects. An increase of light output power by 92.6% is observed for 10 × 10-µm2 mesa size with digital etching, as compared with that with only one step etching and no treatment. We also demonstrated only 1.1% decrease in output power density for a 10 × 10-µm2 LED as compared with a 100 × 100-µm2 device without performing digital etching.

Applying Occam's Razor and Descending the Reconstructive Ladder: The Modified Cheek Advancement Flap for Reconstruction of Nasal Defects.

Nasal reconstruction has important functional and cosmetic considerations, as proper repair of nasal defects is necessary to maintain function of the nasal airway and to recreate the normal appearance of this central facial structure. Cheek advancement flaps provide matched, mobile, and highly vascularized tissue for the reconstruction of nasal defects, allowing for the concealment of incisions within natural creases in a one-stage approach. However, cheek advancement flaps are often underutilized for nasal reconstruction because of their difficulty in restoring nasal contour. We describe reconstruction of 19 nasal dorsal and sidewall defects 0.8 to 3 cm in size. We incorporated a periosteal anchoring suture to maintain/restore nasal contour and additionally removed a half standing cone inferior to the defect to prevent encroachment of the nasal ala or alar crease. All patients were evaluated at least 3 months postoperatively. In all patients, we were able to restore concavity of the nasofacial sulcus, preserve the biconvex nasal tips, prevent alar flaring and retraction, and conserve the alar groove. All patients had excellent functional and cosmetic outcomes. We believe this modified cheek advancement flap provides functionally and aesthetically superior results and can be considered as a first-line approach for repair of nasal dorsal and sidewall defects in subselected patients.

Hyaluronic Acid Gel Incorporating Curcumin-Phospholipid Complex Nanoparticles Prevents Postoperative Peritoneal Adhesion

Peritoneal adhesions following abdominal procedures remain a major surgical issue. This study aimed to evaluate the preventive effect of curcumin-soybean phosphatidylcholine (CUR-SPC) complex-loaded nanoparticles (NPs) embedded in hyaluronic acid (HA) gel. CUR-SPC complex, CUR-SPC NPs, and CUR-SPC-HA gel were fully characterized regarding particle size, zeta potential, morphology, XRD, FTIR, in-vitro release, and rheology. The in vivo efficacy was investigated in a rat model of cecum abrasion and sidewall defect. The optimized spherical-shaped CUR-SPC NPs had a high CUR loading with nanometric particle size (93 nm). CUR-SPC-HA gel showed a pseudoplastic behavior with a homogeneous distribution of CUR-SPC NPs and a sustained release profile over 3 weeks. The inhibitory effect of CUR-SPC-NP-HA gel on fibroblast proliferation and collagen synthesis was evidenced by histopathological (H&E and Masson trichrome staining) and immunohistochemical analyses (vimentin and collagen I expression). Thus, the proposed NP-gel hybrid system could be a promising postoperative anti-adhesion candidate, employing the advantages of CUR, SPC, and HA.

P‐8.8: Investigation of GaN‐based Micro‐LEDs with Sidewall Passivation and KOH Treatment

The luminescence efficiency of Micro‐light emitting diodes (Micro‐LEDs) is determined by external quantum efficiency(EQE). The EQE of Micro‐LEDs decreases with the decrease of device sizes. This droop in peak EQE is due to sidewall defects from plasma‐assisted dry etching, which induce non‐radiative surface recombination. We investigated the effects of atomic‐layer deposition (ALD) sidewall passivation and potassium hydroxide (KOH) treatment on the electrical and defect characteristics of Micro‐LEDs and found that the effects of sidewall damage can be minimized by sidewall treatments. The results indicated that with ALD Al2O3 passivation suppressed the leakage current of devices and with KOH treatment can remove the surface damage.

Reconstruction of Nasal Tip and Right Nasal Sidewall Defects.

Reconstruction of Nasal Tip and Right Nasal Sidewall Defects.

Combination Repair of Nasal Sidewall and Supratip Defect.

Combination Repair of Nasal Sidewall and Supratip Defect.

Generation of sidewall defects in InGaN/GaN blue micro-LEDs under forward-current stress

This work investigates the effect of current stress on InGaN/GaN multiple-quantum-well flip-chip blue micro light-emitting diodes (μ-LEDs) with a mesa size of 30 × 30 μm2 and describes the stress-related mechanisms: defect aggregation and generation, which cause the change in optoelectronic performance of μ-LEDs. A forward-current stress is applied at 75 A/cm2 (0.7 mA) for 200 h. The device performance degrades with increasing stress time except until 25 h. During the initial 25 h of aging, the light output power and the external quantum efficiency (EQE) increase due to the improved crystal quality caused by aggregation of point defects in the active region, which are supported by the ideality factor and the S-parameter. The high-resolution emission-microscope images reveal that the generation of point defects at mesa sidewalls rather than the active region is crucial in performance degradation. We highlight, in particular, that the aging test generates sidewall point defects even though the sidewalls were properly passivated by a thick SiO2 layer. The mechanisms of defect aggregation and generation due to aging are consistently described by the ideality factor, the S-parameter, and the EQE.

Electroluminescence from Single-Walled Carbon Nanotubes with Quantum Defects.

Individual single-walled carbon nanotubes with covalent sidewall defects have emerged as a 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.

Investigation and direct observation of sidewall leakage current of InGaN-Based green micro-light-emitting diodes.

Electrical and optical characteristics of InGaN-based green micro-light-emitting diodes (µLEDs) with different active areas are investigated; results are as follows. Reverse and forward leakage currents of µLED increase as emission area is reduced owing to the non-radiative recombination process at the sidewall defects; this is more prominent in smaller µLED because of larger surface-to-volume ratio. Leakage currents of µLEDs deteriorate the carrier injection to light-emitting quantum wells, thereby degrading their external quantum efficiency. Reverse leakage current originate primarily from sidewall edges of the smallest device. Therefore, aggressive suppression of sidewall defects of µLEDs is essential for low-power and downscaled µLEDs.

An Injectable Peptide Hydrogel Constructed of Natural Antimicrobial Peptide J-1 and ADP Shows Anti-Infection, Hemostasis, and Antiadhesion Efficacy.

Postoperative adhesion is a common complication of abdominal surgery, which always has many adverse effects in patients. At present, there is still a lack of effective treatment measures and materials to prevent adhesion in the clinics. Herein, we report the potential use of J-1-ADP hydrogel formed by natural antimicrobial peptide jelleine-1 (J-1) self-assembling in adenosine diphosphate (ADP) sodium solution to prevent postsurgery adhesion formation. J-1-ADP hydrogel was found to have good antimicrobial activity against the bacteria and fungi tested and can be used to prevent tissue infection, which was thought to be one of the incitements of adhesion. Due to ADP being a platelet-activating factor, J-1-ADP hydrogel showed significant hemostatic activity in vitro verified by whole blood coagulation, plasma coagulation, platelet activation, and platelet adhesion assays. Further, it showed potent hemostatic activity in a mouse liver hemorrhage model. Bleeding was believed to be a cause of the formation of postsurgery adhesion. J-1-ADP hydrogel had a significant antiadhesion effect in a rat side wall defect-cecum abrasion model. In addition, it had good biocompatibility and degradation properties. So the present study may provide an alternative strategy for designing antimicrobial peptide hydrogel material to prevent postoperative adhesion formation in the clinic.

Lateral Nasal Artery Perforator Flap for Nasal Reconstruction: Clinical Applications and Risk Factors Associated With Nasal Deformities.

Nasal reconstruction is challenging because of the difficulty in balancing superior aesthetic outcomes and less invasive surgery. The use of the lateral nasal artery (LNA) perforator flap has been reported for nasal reconstruction. However, few reports have described appropriate applications of nasal reconstruction and assessments of nasal deformity. This study aimed to quantify the aesthetic outcomes on using this flap and reveal the risk factors associated with nasal deformities. Twenty patients underwent nasal reconstruction using the LNA flap with a cranial perforator adjacent to the nasal defect. Postoperative protuberant deformities were scored by 2 independent plastic surgeons using a 5-point Likert scale and classified as excellent, good, or poor. The risk factors of deformities were identified using univariate analyses. A nasal alar deviation index was developed to analyze correlations with flap harvesting. The sensory function was assessed by the Semmes-Weinstein test. Flaps survived in 19 patients (95%), and 1 flap showed distal necrosis. All arterial perforators used remained within 5 mm lateral to the boundary between the cheek and nasal ala. The flaps were most often used to cover 2 subunits, including the nasal sidewall defects. Protuberant deformities in 6 (30%), 8 (40%), and 6 (30%) patients were classified as excellent, good, and poor, respectively. Nasal defects involving more than 3 subunits caused severe protuberant deformity. Only 2 patients (5%) in the good and fair groups underwent additional debulking surgery. Nasal alar deviation was not significantly correlated with flap harvesting, when the nasal alar deviation index before and after surgery were compared. Sensory function was retained in all patients. Aesthetic outcomes and sensory function were good on using the LNA perforator flap as a propeller flap having a wide arc of rotation. This flap is suitable for nasal reconstruction involving less than 2 nasal subunits without any severe nasal alar deviation deformity. In addition, this flap allows for better outcomes because it requires less invasive 1-stage surgery.

Study on the effect of size on InGaN red micro-LEDs

In this research, five sizes (100 × 100, 75 × 75, 50 × 50, 25 × 25, 10 × 10 µm2) of InGaN red micro-light emitting diode (LED) dies are produced using laser-based direct writing and maskless technology. It is observed that with increasing injection current, the smaller the size of the micro-LED, the more obvious the blue shift of the emission wavelength. When the injection current is increased from 0.1 to 1 mA, the emission wavelength of the 10 × 10 μm2 micro-LED is shifted from 617.15 to 576.87 nm. The obvious blue shift is attributed to the stress release and high current density injection. Moreover, the output power density is very similar for smaller chip micro-LEDs at the same injection current density. This behavior is different from AlGaInP micro-LEDs. The sidewall defect is more easily repaired by passivation, which is similar to the behavior of blue micro-LEDs. The results indicate that the red InGaN epilayer structure provides an opportunity to realize the full color LEDs fabricated by GaN-based LEDs.

Repair of Combination Nasal Sidewall and Paranasal Cheek Defects.

*All authors are affiliated with the Department of Dermatology, University of Cincinnati Medical Center, Cincinnati, Ohio Address correspondence and reprint requests to: Scott A. Neltner, MD, Department of Dermatology, University of Cincinnati Medical Center, 2701 Chancellor Dr., Crestview Hills, KY 41017, or e-mail: [email protected] The authors have indicated no significant interest with commercial supporters.

PuraStat RADA16 Self-Assembling Peptide Reduces Postoperative Abdominal Adhesion Formation in a Rabbit Cecal Sidewall Injury Model

Objective: To evaluate the effect of PuraStat (2.5% RADA16) administration on postoperative abdominal adhesion formation in an in vivo model. Methods: Anesthetized New Zealand white rabbits underwent cecal sidewall abrasion surgery in which the cecal serosa and juxtaposed parietal peritoneum were abraded after access through an abdominal midline incision. Eight animals were randomized to receive PuraStat administration at the interface of the injured tissues before incision closure, and five animals served as untreated controls. Treated animals received 3–12 ml PuraStat solution per lesion. Animals were sacrificed 14 days after surgery and examined for adhesion formation at the wound site. Results: At study terminus, adhesions were identified in 90% (9/10) of abraded cecum/peritoneal wound sites in untreated controls versus 25% (4/16) of PuraStat-treated sites (p = 0.004). Mean ± SD Total Adhesion Score (average of the values for extent + strength of the adhesion in both defects per animal; maximum score = 14 points) was significantly 76% lower in PuraStat-treated animals (2.0 ± 3.0 points) compared to untreated controls (8.2 ± 1.9 points) (p = 0.029). Mean adhesion coverage area of wound sites was 79% lower in PuraStat-treated animals than controls (p < 0.001), and mean adhesion durability was 72% lower in PuraStat-treated animals versus controls (p = 0.005). Remnant hydrogel was observed at the wound sites of 75% of treated animals at postoperative Day 14. Conclusion: PuraStat treatment has a positive protective effect in the cecal sidewall injury model, and significantly reduces abdominal adhesion formation at the interface of the injured cecum and overlying peritoneal sidewall defect.

Improved electro-optical and photoelectric performance of GaN-based micro-LEDs with an atomic layer deposited AlN passivation layer.

The quantum efficiency of GaN-based micro-light-emitting diodes (micro-LEDs) is of great significance for their luminescence and detection applications. Optimized passivation process can alleviate the trapping of carriers by sidewall defects, such as dangling bonds, and is regarded as an effective way to improve the quantum efficiency of micro-LEDs. In this work, an AlN passivation layer was prepared by atomic layer deposition to improve the electro-optical and photoelectric conversion efficiency in GaN-based micro-LEDs. Compared to conventional Al2O3 passivation, the AlN passivation process has a stronger ability to eliminate the sidewall defects of micro-LEDs due to the homogeneous passivation interface. Our experiments show that the AlN-passivated device exhibits two orders of magnitude lower forward leakage and a smaller ideality factor, which leads to significantly enhanced external quantum efficiency (EQE). For 25*25 μm2 micro-LEDs, the EQE of the AlN-passivated device was 18.3% and 57.7% higher than that of the Al2O3-passivated device in luminescence application and detection application, respectively.