Eun-Kyung Chu's research works | Korea Advanced Nano Fab Center and other places

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(a) Schematic of the epitaxy structure of InGaN/GaN red micro-LED. (b) Transmission electron microscope (TEM) image of the grown epitaxial layer. (c) The fabrication process flow of InGaN/GaN red micro-LED on a 4-inch wafer scale.

(a) Current density-voltage (J-V) characteristic of InGaN/GaN MQW red micro-LEDs depending on device sizes. (b) Optical microscope images of 12 µm arrays and 100 µm arrays with increasing input current density from 1 to 10 A/cm². (c) Electroluminescence spectra for 12 µm pixels at input current densities ranging from 3 to 30 A/cm². (d) Dominant wavelength and (e) EQE of InGaN/GaN MQW red micro-LEDs with different device sizes. (f) Performances of InGaN/GaN red micro-LEDs grown on Si substrates reported recently.

InGaN/GaN red micro-LEDs passive array driving images. A 1692 PPI array of a dog image with a 12 µm pitch, and a dog and cat image in a 4232 PPI array with a 5 µm pitch size. Measurements were conducted by increasing the current density from 1 to 10 A/cm².

(a) Input voltage and current density pulse injected into a 12 µm pixel of InGaN/GaN red micro-LED, targeting the 3 A/cm² injection. (b) EL spectra and (c) luminance with increasing turn-on duty cycle from 10 to 90%.

Size-dependent optoelectronic characteristics of InGaN/GaN red micro-LEDs on 4-inch Si substrates: high pixel density arrays demonstration

June 2024

28 Reads

Optics Express

[...]

In this study, we explored the size-dependent optoelectronic characteristics of InGaN/GaN red micro-LEDs grown on Si substrates. We successfully demonstrated the fabrication of 4-inch wafer-scale InGaN/GaN micro-LEDs, showcasing the feasibility of large-scale production. Additionally, we presented the binary pixel display with 6 µm pitch, achieving a resolution of 4232 PPI. We also introduced a method of driving the display using PWM to linearly control and counteract the blue shift in peak wavelength caused by the QCSE and band-filling effect. Our research represents a significant milestone in the development of InGaN/GaN red micro-LEDs on Si substrates, establishing them as a key component for full-color micro-LED displays.

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Figure 1. Schematic diagram of the fabrication process used to create the blue micro-LED arrays.

Wafer-Scale Characterization of 1692-Pixel-Per-Inch Blue Micro-LED Arrays with an Optimized ITO Layer

April 2024

38 Reads

Micromachines

[...]

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays were fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). Although the sputter-deposited ITO (S-ITO) films exhibited a densely packed morphology and lower resistivity compared to the e-beam-deposited ITO (E-ITO) films, the forward voltage (VF) values of a micro-LED with the S-ITO films were higher than those with the E-ITO films. The VF values for a single pixel and for four pixels with E-ITO films were 2.82 V and 2.83 V, respectively, while the corresponding values for S-ITO films were 3.50 V and 3.52 V. This was attributed to ion bombardment damage and nitrogen vacancies in the p-GaN layer. Surprisingly, the VF variations of a single pixel and of four pixels with the optimized E-ITO spreading layer from five different regions were only 0.09 V and 0.10 V, respectively. This extremely uniform VF variation is suitable for creating micro-LED displays to be used in AR and VR applications, circumventing the bottleneck in the development of long-lifespan and high-brightness organic LED devices for industrial mass production.

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Figure 2. Top-view SEM images of E-ITO films: ((a) at 100,000 X and (b) at 200,000 X) and S-ITO films ((c) at 100,000 X and (d) at 200,000 X), and histograms showing the grain size distributions of (b) for (e) the E-ITO films and (d) for (f) the S-ITO films.

Figure 3. Two-dimensional (2D) and three-dimensional (3D) AFM images of a p-GaN layer, and 2D and 3D AFM images of E-ITO film and S-ITO film deposited onto a p-GaN layer.

Figure 4. J-V characteristics of blue micro-LEDs for a single pixel and for four pixels with the E-ITO films and S-ITO films.

Figure 5. Wafer-scale uniformity of the VF characteristics of blue micro-LED arrays for a single pixel and for four pixels using an E-ITO spreading layer with five different regions.

Wafer-Scale Characterization of 1692-Pixel-Per-Inch Blue Micro-LED Arrays with an Optimized ITO Layer

March 2024

28 Reads

[...]

Wafer-scale blue micro-light-emitting diode (micro-LED) arrays are fabricated with a pixel size of 12 μm, a pixel pitch of 15 μm, and a pixel density of 1692 pixels per inch, achieved by optimizing the properties of e-beam-deposited and sputter-deposited indium tin oxide (ITO). Although the sputter-deposited ITO (S-ITO) films exhibit a densely packed morphology and lower resistivity compared to those of the e-beam-deposited ITO (E-ITO) films, the forward voltage (VF) values of a micro-LED with the S-ITO films are higher than those with the E-ITO films. The VF values for a single pixel and for four pixels with E-ITO films are 2.82 V and 2.83 V, respectively, while the corresponding values for S-ITO films are 3.50 V and 3.52 V. This was attributed to ion bombardment damage and nitrogen vacancies in the p-GaN layer. Surprisingly, the VF variations of a single pixel and of four pixels with the optimized E-ITO spreading layer from five different regions are only 0.09 V and 0.10 V, respectively. This extremely uniform VF variation is suitable for realizing micro-LED displays to be used in AR and VR applications, circumventing the bottleneck in the development of long-lifespan and high-brightness organic LED devices for industrial mass production.

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Eun-Kyung Chu's research while affiliated with Korea Advanced Nano Fab Center and other places

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