Size-Dependent Electroluminescence and Current-Voltage Measurements of Blue InGaN/GaN µLEDs down to the Submicron Scale

Wolter, S.; Spende, Hendrik; Gülink, Jan; Hartmann, Jana; Wehmann, H.-H.; Waag, A.; Lex, A.G.; Avramescu, Adrian; Lugauer, H.‐J.; Malm, Norwin von; Drolet, Jean-Jacques P.; Straßburg, Martin

doi:10.3390/nano11040836

Cited by 21 publications

(10 citation statements)

References 27 publications

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“…For both geometries, the I(RT)/I(LT) ratio increases from 2.5 up to 7.5 μm, corresponding to the mesas where the entire volume or nearly the entire volume is affected by the SRH recombination through sidewall defects due to extensive carrier diffusion (around 3.5 μm). 41 In the case of the square mesas, there is a subsequent attenuation of this increase as the relative importance of SRH recombination diminishes with the surface-to-perimeter ratio. A sudden decrease in I(RT)/ I(LT) is observed for the 10 μm circular mesa.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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

González-Izquierdo,

Rochat,

Zoccarato

et al. 2023

ACS Photonics

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Micro light-emitting diodes (μLEDs) are expected to revolutionize the display technology due to their advantages over the current LCD and OLED technology and the possibility to use them in micro displays, visible light communications, and optogenetics. One of the main challenges of this emergent technology is the efficiency drop with the reduction of LED size due to sidewall defects. In this article, we study the size and shape dependence of the external quantum efficiency by cathodoluminescence measurements at room temperature and 10 K. Our results show that, for small μLEDs (between 2.5 and 10 μm width), there is an optimal intermediate LED size for which the light emission is maximized, which we attribute to a competition between the light extraction efficiency (LEE) (which decreases with LED size) and the internal quantum efficiency (IQE) (which increases with LED size). In contrast to most prior studies that typically examine either the IQE or LEE with respect to size for larger LEDs, our work stands out by examining the interplay between IQE and LEE for μLEDs below 10 μm. These results are of high relevance for the design of μLED arrays and show the need for understanding the evolution of LEE and sidewall nonradiative recombination with LED geometry and size.

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Section: ■ Results and Discussionmentioning

confidence: 99%

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

González-Izquierdo,

Rochat,

Zoccarato

et al. 2023

ACS Photonics

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“…Thus, the emission of the 100 µm 2 ‐µLEDs is strongly influenced by light extraction than that of the 400 µm 2 ‐µLEDs. [ 51–54 ] Taken together, the EQE of the 100 µm 2 ‐µLEDs decreases after TMAH treatment even though the IQE increases because the sidewall smoothening reduces the light extraction.…”

Section: Resultsmentioning

confidence: 99%

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

Park

Pristovsek

Cai

et al. 2023

Advanced Optical Materials

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The sidewall condition is a key factor determining the performance of micro-light emitting diodes (μLEDs). In this study, we prepared equilateral triangular III-nitride blue μLEDs with exclusively m-plane sidewall surfaces to confirm the impact of sidewall conditions. It was found that inductively coupled plasma-reactive ion etching (ICP-RIE) caused surface damages to the sidewall and resulted in rough surface morphology. As confirmed by time-resolved photoluminescence (TRPL) and X-ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminated the etching damage and flattened the sidewall surface. After ICP-RIE, 100 µm 2 -micro-LEDs (µLEDs) yielded higher external quantum efficiency (EQE) than 400 µm 2 -µLEDs. However, after TMAH treatment, the peak EQE of 400 µm 2 -µLEDs increased by around 10% in the low current regime, whereas that of 100 µm 2 -µLEDs slightly decreased by around 3%. The EQE of the 100 µm 2 -µLED decreased after TMAH treatment although the internal quantum efficiency (IQE) increased. Further, the IQE of the 100 µm 2 -µLEDs before and after TMAH treatment was insignificant at temperatures below 150 K, above which it became considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non-radiative recombination rate and light extraction.

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“…Alternatively, a flipchip approach with backside emission through the sapphire substrate would increase the extraction efficiency [17]. The impact of sidewall defects at the plasma-etched fins, especially affecting the IQE in case of smaller pixels, could be reduced by additional passivation measures [38], [39].…”

Section: Discussionmentioning

confidence: 99%

Processing and Characterization of Monolithic Passive-Matrix GaN-Based MicroLED Arrays With Pixel Sizes From 5 to 50 µm

et al. 2021

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MicroLED arrays with the capability of switching each pixel separately with high frequency can serve as structured micro-illumination light engines for applications in sensing, optogenetics, microscopy and many others. We describe a scalable chip process chain for the fabrication of passive-matrix microLED arrays, which were integrated with PCB-based driving electronics. The arrays were produced by deep-etching of conventional planar LED structures on sapphire, followed by filling and planarization steps. The pixel resolution lies in the range of 254 to 2540 pixelsper-inch (ppi), the arrays consist of 32 x 32 pixels. Optical output powers up to 50 µW per pixel were measured. In comparison to CMOS-based approaches, the presented technology is a simplified strategy to produce microLED arrays with high pixel counts.

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Size-Dependent Electroluminescence and Current-Voltage Measurements of Blue InGaN/GaN µLEDs down to the Submicron Scale

Cited by 21 publications

References 27 publications

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

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

Processing and Characterization of Monolithic Passive-Matrix GaN-Based MicroLED Arrays With Pixel Sizes From 5 to 50 µm

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