Sidewall Treatment Research Articles

Increasing Efficiency and Extending Lifetime of Red Micro Light-Emitting Diodes Through Sidewall Treatment for Improved Reliability

Increasing Efficiency and Extending Lifetime of Red Micro Light-Emitting Diodes Through Sidewall Treatment for Improved Reliability

Impacts and effectiveness of sidewall treatment on the spatially resolved optical properties and efficiency enhancement for GaN-based blue and green micro-LEDs

InGaN-based micro-light-emitting diodes (micro-LEDs) are crucial for efficient full-color micro-displays, but suffer from severe degradation of external quantum efficiency (EQE) with size reduction. In this study, the impacts of chemical treatment on the sidewall condition and the EQE of the 10 μm InGaN-based blue and green micro-LEDs were demonstrated. The sidewall treatment can effectively alleviate the residual damage caused by dry etching and suppress the nonradiative recombination, facilitating the achievement of high internal quantum efficiency (IQE). Nevertheless, the sidewall light extraction of the micro-LEDs with smoother sidewall morphology after tetramethylammonium hydroxide (TMAH) treatment is lower than those with rough and prismatic sidewall surface. By utilizing microscopic hyperspectral imaging, the difference in chromatic properties between the inner region and the whole micro-LED caused by dry etching can hinder the stability of chromatic properties of InGaN-based blue micro-LEDs, which can be alleviated by sidewall treatment. The optimal duration for TMAH treatment is obtained as 10 min for both blue and green micro-LEDs, which is the consequence of the compromise between sidewall light extraction efficiency (LEE) and IQE, whereas the improvement of IQE by sidewall treatment for green micro-LEDs is less significant compared to that for blue ones, which can be attributed to the higher dislocation density and recombination via localized states of green InGaN micro-LEDs. This work demonstrates the evolution of IQE and LEE for blue and green micro-LEDs with different sidewall treatment strategies to achieving the ultimate EQE.

P‐141: Ultrafine‐pitch AlGaN Ultraviolet‐C microLED Displays for Quantum Dots Color Conversion

Aluminum Gallium Nitride (AlGaN) ultraviolet‐C (UV‐C) micro‐light‐emitting diodes (microLEDs) offer significant advantages in terms of convenience, cost‐effectiveness, and environmental friendliness, positioning them as promising candidates for display applications. However, achieving the desired high efficiency and scalability for large displays with ultra‐fine pixels necessitates substantial progress beyond current experimental outcomes. This study showcases the application of AlGaN UV‐C microLED display panels and micro‐displays incorporating quantum dots (QDs) for color conversion. Sidewall treatment and atomic layer deposited (ALD) passivation effectively address dangling bonds and etching damages, leading to a notable enhancement of TM‐polarized light extraction efficiency (LEE). Moreover, dedicated strain modulation efforts successfully reduce the high Al content (over 50%) wafer bowling effect, facilitating the modularization of ultrafine‐pitch AlGaN UV‐C microLED panels. Consequently, the devices achieve a peak performance of over 5% external quantum efficiency (EQE) as the mesa size scales down to 3 μm. The highlighted 0.18‐inch UV‐C microLED display panels, featuring a 9 μm pixel size, are precisely controlled by a CMOS IC driver to achieve desired patterns. Serving as an efficient pumping source for perovskite quantum dots paper (PQDP), this UV‐C microLED display suggests the potential to revolutionize the full‐color display industry by providing an innovative and unconventional solution.

Optical analysis of III-nitride micro-light-emitting diodes with different sidewall treatments at low current density operation

In this work, the optical efficiency of III-nitride blue micro-LEDs (μLEDs) ranged from 5 × 5 to 60 × 60 μm2 with different sidewall treatments at low current density range was investigated. The results showed dielectric sidewall passivation using atomic layer deposition (ALD) has superior optical enhancement compared to conventional RF sputtering, where most of the enhancement occurred at low current density range. Additionally, the use of ALD sidewall passivation and chemical treatment offered significant efficiency improvement for different sizes of μLEDs at operating less than 1 A cm−2 and the devices without sidewall treatments did not emit light. The effect of sidewall treatments to the effective Shockley–Read–Hall (SRH) nonradiative recombination coefficient, or the effective A coefficient from the ABC model, was estimated. The effective SRH nonradiative recombination coefficient was suppressed by two orders of magnitude for devices with sidewall treatments compared to devices without sidewall passivation.

Improved Performance of AlGaInP Red Micro Light-Emitting Diodes by Sidewall Treatments of Citric Acid

Improved Performance of AlGaInP Red Micro Light-Emitting Diodes by Sidewall Treatments of Citric Acid

Study on the Influence of KOH Wet Treatment on Red μLEDs

InGaN-based red micro-light-emitting diodes (µLEDs) of different sizes were prepared in this work. The red GaN epilayers were grown on 4-inch sapphire substrates through metal-organic chemical vapor deposition (MOCVD). Etching, sidewall treatment, and p- and n-contact deposition were involved in the fabrication process. Initially, the etching process would cause undesirable damage to the GaN sidewalls, which leads to an increase in leakage current. Hence, we employed KOH wet treatment to rectify the defects on the sidewalls and conducted a comparative and systematic analysis of electrical as well as optical properties. We observed that the µLEDs with a size of 5 µm exhibited a substantial leakage current, which was effectively mitigated by the application of KOH wet treatment. In terms of optical performance, the arrays with KOH demonstrated improved light output power (LOP). Additionally, while photoelectric performance exhibited a decline with increased current density, the devices treated with KOH consistently outperformed their counterparts in terms of optoelectronic efficiency. It is noteworthy that the optimized devices displayed enhanced photoelectric characteristics without significantly altering their original peak wavelength and FWHM. Our findings point to the elimination of surface non-radiative recombination by KOH wet treatment, thereby enhancing the performance of small-sized red µLEDs, which has significant potential in realizing full-color micro-displays in near-eye projection applications.

Recovering the efficiency of AlGaInP red micro-LEDs using sidewall treatments

A sidewall treatment process is proposed to recover the external quantum efficiency (EQE) loss in AlGaInP micro-LEDs (μLEDs). The proposed sidewall treatment consists of thermal annealing, ammonium sulfide chemical treatment, and sidewall passivation using atomic-layer deposition (ALD). The devices with sidewall treatment show improved optical power of more than 500% and 190% at 5 and 100 A cm−2, respectively, compared to devices with ALD sidewall passivation. The reduction in EQE was 20% when shrinking the device dimensions from 100 × 100 to 20 × 20 μm2. This work reveals that AlGaInP μLEDs can be energy efficient by employing proper sidewall treatments.

Metamaterials for light extraction and shaping of micro-scale light-emitting diodes: from the perspective of one-dimensional and two-dimensional photonic crystals.

Metamaterials have attracted broad attention owing to their unique versatile micro- and nano-structures. As a kind of typical metamaterial, photonic crystals (PhCs) are capable of controlling light propagation and constraining spatial light distribution from the chip level. However, introducing metamaterial into micro-scale light-emitting diodes (µLED) still exists many unknowns to explore. This paper, from the perspective of one-dimensional and two-dimensional PhCs, studies the influence of metamaterials on the light extraction and shaping of µLEDs. The µLEDs with six different kinds of PhCs and the sidewall treatment are analyzed based on finite difference time domain (FDTD) method, in which the optimal match between the PhCs type and the sidewall profile is recommended respectively. The simulation results show that the light extraction efficiency (LEE) of the µLEDs with 1D PhCs increases to 85.3% after optimizing the PhCs, and is further improved to reach 99.8% by the sidewall treatment, which is the highest design record so far. It is also found that the 2D air ring PhCs, as a kind of left-handed metamaterials, can highly concentrate the light distribution into 30° with the LEE of 65.4%, without help of any light shaping device. The surprising light extraction and shaping capability of metamaterials provides a new direction and strategy for the future design and application of µLED devices.

A review of the effect of GaN-Based Micro-LED sidewall on external quantum efficiency and sidewall treatment techniques

A review of the effect of GaN-Based Micro-LED sidewall on external quantum efficiency and sidewall treatment techniques

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.

Optical and microstructural characterization of Micro-LED with sidewall treatment

The traditional influence on the sidewall damage of Micro-LED was mostly focused on the research of I-V-L. In this paper, we discussed the influence of Micro-LED sidewall damage from the perspective of optical and microstructural characterization. Scanning electron microscopy showed that the Micro-LED structure with smaller size was more irregular after inductively coupled plasma etching. High-resolution transmission electron microscopy and energy dispersive x-ray spectroscopy analysis showed that the area of the upper and lower regions of the quantum well was inconsistent, there was about 2 nm lattice disorder on the surface of the sidewall of the mesa, and oxygen and silicon impurity atoms were enriched. For optical characterization, a method combining laser scanning confocal microscopy and photoluminescence (PL) was proposed to evaluate the optical performance of the mesa. The results showed that the luminescence of Micro-LED mesa was uneven, the luminous intensity at the edge of the mesa was reduced by more than 65%, and the luminous wavelength was shifted by several nanometers. Finally, we optimized the sidewall treatment process, effectively improved the performance of Micro-LED devices by combining tetramethylammonium hydroxide treatment and SiO2 passivation, and increased the luminous intensity of Micro-LED 2 μm away from the edge by about 4.7 times and PL uniformity was greatly improved. These results provided an available reference for the development of Micro-LED.

Analysis of size dependence and the behavior under ultrahigh current density injection condition of GaN-based Micro-LEDs with pixel size down to 3 μm

In this paper, the GaN-based green micro light-emitting diodes (Micro-LEDs) with various sizes (from 3 to 100 μm) were fabricated and electro-optically characterized. Atom layer deposition (ALD) passivation and potassium hydroxide (KOH) treatment were applied to eliminate the sidewall damage. The size dependence of Micro-LED was systematically analyzed with current-versus-voltage and current density-versus-voltage relationship. According to the favorable ideality factor results (<1.5), the optimized sidewall treatment was achieved when the device size shrank down to <10 μm. In addition, the external quantum efficiency (EQE) droop phenomenon, luminance and output power density characteristics were depicted up to the highest current density injection condition to date (120 kA cm−2), and 6 μm device exhibited an improved EQE performance with the peak EQE value of 16.59% at 20 A cm−2 and over 600k and 6M cd cm−2 at 1 and 10 A cm−2, indicating a greater brightness quality for over 3000 PPI multiple display application. Lastly, the blue shift of 6 μm device with elevating current density was observed in electroluminescence spectra and converted to CIE 1931 color space. The whole shifting track and color variation from 1 A cm−2 to 120 kA cm−2 were demonstrated by color coordinates.

Increase in the efficiency of III-nitride micro LEDs by atomic layer deposition.

The effect of atomic-layer deposition (ALD) sidewall passivation on the enhancement of the electrical and optical efficiency of micro-light-emitting diode (µ-LED) is investigated. Various blue light µ-LED devices (from 5 × 5 µm2 to 100 × 100 µm2) with ALD-Al2O3 sidewall passivation were fabricated and exhibited lower leakage and better external quantum efficiency (EQE) comparing to samples without ALD-Al2O3 sidewall treatment. Furthermore, the EQE values of 5 × 5 and 10 × 10 µm2 devices yielded an enhancement of 73.47% and 66.72% after ALD-Al2O3 sidewall treatments process, and the output power also boosted up 69.3% and 69.9%. The Shockley-Read-Hall recombination coefficient can be extracted by EQE data fitting, and the recombination reduction in the ALD samples can be observed. The extracted surface recombination velocities are 551.3 and 1026 cm/s for ALD and no-ALD samples, respectively.

High efficiency blue InGaN microcavity light-emitting diode with a 205 nm ultra-short cavity

High-efficiency blue InGaN-based semipolar (20-2-1) ultra-short microcavity light-emitting diodes (MC-LEDs) with a cavity length of 205 nm were demonstrated. A peak external quantum efficiency (EQE) of 7.3%, the value of which is almost the same as 10% of conventional c-plane micrometer-sized microlight-emitting diodes with a device thickness of ∼5 μm grown on the sapphire substrate, was achieved. The emission wavelength is 431 nm at the current density of 297 A/cm2. In order to obtain high-efficiency MC-LEDs, a sidewall treatment was performed by using buffered hydrofluoric acid and phosphoric acid (H3PO4) to remove the dry etching residue and the surface damage. The demonstration of MC-LEDs with a high EQE and a single mode emission should pave the way for the application to display and others.

Improved performance of AlGaInP red micro-light-emitting diodes with sidewall treatments.

The electrical and optical improvements of AlGaInP micro-light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) sidewall passivation were demonstrated. Due to the high surface recombination velocity and minority carrier diffusion length of the AlGaInP material system, devices without sidewall passivation suffered from high leakage and severe drop in external quantum efficiency (EQE). By employing ALD sidewall treatments, the 20×20 µm2 µLEDs resulted in greater light output power, size-independent leakage current density, and lower ideality factor. The forward current-voltage characteristic was enhanced by using surface pretreatment. Furthermore, ALD sidewall treatments recovered the EQE of the 20×20 µm2 devices more than 150%. This indicated that AlGaInP µLEDs with ALD sidewall treatments can be used as the red emitter for full-color µLED display applications.

Size-independent peak efficiency of III-nitride micro-light-emitting-diodes using chemical treatment and sidewall passivation

Micro-light-emitting-diodes (μLEDs) with size-independent peak external quantum efficiency behavior was demonstrated from 10 × 10 μm2 to 100 × 100 μm2 by employing a combination of chemical treatment and atomic-layer deposition (ALD) sidewall passivation. The chemical treatment and sidewall passivation improved the ideality factors of μLEDs from 3.4 to 2.5. The results from the combination of chemical treatment and ALD sidewall passivation suggest the issue of size dependent efficiency can be resolved with proper sidewall treatments after dry etching.

High efficiency of III-nitride micro-light-emitting diodes by sidewall passivation using atomic layer deposition.

Optoelectronic effects of sidewall passivation on micro-sized light-emitting diodes (µLEDs) using atomic-layer deposition (ALD) were investigated. Moreover, significant enhancements of the optical and electrical effects by using ALD were compared with conventional sidewall passivation method, namely plasma-enhanced chemical vapor deposition (PECVD). ALD yielded uniform light emission and the lowest amount of leakage current for all µLED sizes. The importance of sidewall passivation was also demonstrated by comparing leakage current and external quantum efficiency (EQE). The peak EQEs of 20 × 20 µm2 µLEDs with ALD sidewall passivation and without sidewall passivation were 33% and 24%, respectively. The results from ALD sidewall passivation revealed that the size-dependent influences on peak EQE can be minimized by proper sidewall treatment.

Drainage Performance of Different Sizes Tire Chips used Alone and Mixed with Natural Aggregates as Leachate Drainage Layer Material

Results of compressibility and hydraulic conductivity testing performed under different levels of average vertical stress were used to determine the appropriate tire chips size (in particular aspect ratio) and tire chip—gravel random state mix combination. Proper sidewall treatment was provided to reduce side wall friction up to minimum level and constant head conditions were maintained with appropriate design flow rate. Results showed that tire chips (length 25 mm, aspect ratio 1) mixed with 40 mm gravel in the random state in mixing ratio of 3:1 (ds:dg) was observed to undergo minimum strain, maximum hydraulic conductivity and hence free drainage even under high vertical stress levels. By selecting tire chips of appropriate aspect ratio and optimum mix combination for the construction of drainage layer of MSW landfill leachate collection system lower strain response, higher hydraulic conductivity values and relatively free drainage even under anticipated higher vertical stress levels may be achieved.

Validation of a polyimide foam model for use in transmission loss applications.

In this paper, the use of polyimide foam as a lining in double panel applications is considered. Polyimide foam has a number of attractive functional attributes, not the least of which is its high fire resistance, thus making its use desirable in some sound transmission applications. The configuration studied here consisted of two 0.04×94 thick, flat aluminum panels separated by 5 in., with a 3 in. thick layer of foam centered in that space. Random incidence transmission loss measurements were conducted on this buildup, and conventional poro-elastic models were used to predict the performance of the lining material. The Biot parameters of the foam were determined by a combination of direct measurement (for density, flow resistivity and Young’s modulus) and inverse characterization procedures (for porosity, tortuosity, viscous and thermal characteristic length, Poisson’s ratio, and loss factor). The inverse characterization procedure involved matching normal incidence standing wave tube measurements of absorption coefficient and transmission loss of the isolated foam with finite element predictions. When the foam parameters determined in this way were used to predict the performance of the complete double panel system, reasonable agreement between the measured transmission loss and predictions made using commercial statistical energy analysis codes was obtained.

Structure-borne noise transmission in the Propfan Test Assessment aircraft

Estimates of the level of structure-bor ne noise transmission in the Propfan Test Assessment (PTA) aircraft were carried out for the first three blade passage frequencies. The procedure used combined the frequency response functions of cabin sound pressure level to wing strain response obtained during ground test of the PTA aircraft with in-flight measured wing strain response data. The estimated structure-borne noise levels varied from 64 to 84 dB showing very little dependence on engine/propel ler power, flight altitude, or flight Mach number. In general, the bare cabin in-flight noise levels decreased with increasing propeller tone frequency, giving rise to a plausible structure-borne noise transmission problem at the higher frequency blade passage tones. Without knowledge of the effects of a high insertion loss sidewall treatment on structure-bor ne noise transmission of the bare cabin no quantitative conclusions could be made on the level of structure-borne noise transmission in a treated production aircraft.