Sidewall defects

Pyramidical GaN microLED developer Polar Light Technologies announced that it has managed to produce red (625 nm) microLEDs based on its non-etching bottom-up platform. The company now has demonstrated the production of red, green and blue pyramidal microLEDs using the same material compound. 

Red is the most challenging microLED emitter, and companies have been looking at several alternatives to native GaN red microLEDs, including 3D nanowires, color conversion, and color tunable LEDs.  Polar Light Technologies’ microLED is composed of pyramid shapes that are built with a novel bottom-up approach, a technology that the company says comes with unique benefits, including reduced strain in the lattice of the InGaN/GaN structure, a unique possibility of frontplane integration, no etching damage (and so higher efficiency), ability to produce small microLEDs, even sub-micron, a narrow emission cone and more. 

Researchers from the Chemnitz University of Technology have combined several new technologies to enable high density high-brightness microLED displays. The researchers demonstrated a 3400 PPI 1080x780 monochrome green display with a brightness of over 10,000,000 nits.

To achieve this high performance display, the researchers used wafer-scale high-quality epitaxial growth, sidewall passivation, efficient photon extraction, and elegant bonding technologies.

Finland-Based Comptek Solutions announced that it has successfully designed and installed a pilot line that integrates its Kontrox passivation technology with industry-standard techniques like Atomic Layer Deposition (ALD) for substrates up to 200mm. The company says that its technology minimizes surface defects and ensuring an exceptionally high-quality III-V dielectric interface.

The new facility enables Comptek to deliver scalable solutions for a wide range of applications, including power electronics and optoelectronics. One of the key applications for Comptek are microLED devices. Back in 2022, we posted a spotlight on Comptek and a short interview with its CEO, that highlights how the performance of microLED devices is increased thanks to the passivation technology.

Finland based Comptek Solutions announced that it has successfully closed its its Series A funding round, raising a total of 8 million Euro, from the Horizon Europe EIC Fund, LIFTT (Italian venture firm) and an undisclosed key strategic partner.

The funds will be used to accelerate Comptek's technology implementation, and scale up its growth. Comptek was founded in 2017, and develops passivation technology for Optoelectronics and power applications.

Researchers from Korea's KAIST have found that by changing the epitaxial structure of microLEDs, it is possible to fundamentally resolve the problem of efficiency degradation in microLED devices. In other words, it is possible to create microLEDs in which the efficiency does not drop with size. 

The researchers discovered that the specific epitaxial structure of the microLED changes how the current drives to the sidewall of the microLEDs. Based on that, the researchers developed a epitaxial structure that is not sensitive to sidewall defects. The proposed structure also reduces generated heat by about 40% compared to standard microLEDs.

China-based MicroLED microdisplay developer Jade Bird Display announced that it is developing a native full-color microLED microdisplay. JBD is working to integrate InGaN and AlInGaP on the same chip, fabricated using conventional thin-film processes.

JBD says it developed a proprietary (and patented) technology in which the epitaxy layers were designed to be less susceptibility to edge effects, which helps to increase the display's efficiency. JBD's technology also enables effective mesa sidewall passivation. JBD refers to its technology as monolithic hybrid integration and says it can reach a PPI of up to 10,000 with a pixel pitch of 2.5 um.

Researchers from King Abdullah's University of Science & Technology (KAUST) in Saudi Arabia developed GaN and InGan red microLED devices that are highly efficient.

The researchers managed to increase the efficiency of their previous design by a new chemical treatment that removes damages at the microLED sidewalls (created during the fabrication process) and also retains the high crystal quality at the InGaN and GaN sidewall interfaces.

This article is a first article in a short series of articles that discuss the efficiency of microLED displays. And we start with the quantum efficiency of microLED chips.

LED devices are quite efficient. In the chart above (by the DoE), you can see that the efficiency (external quantum efficiency, or EQE) of a blue LED is around 70%. It is generally accepted that as LED chip size decreases, the efficiency of LED devices decreases as well.