Prof. Xuelun Wang | National Institute of Advanced Industrial Science and Technology (AIST): Can We Eliminate Side-Wall Damage in Sub-3-Micron LEDs Without Sacrificing Efficiency?

Can molecular beam epitaxy eliminate the devastating size-dependent efficiency loss in sub-five-micron microLEDs?

The miniaturization of microLEDs for next-generation displays has been bottlenecked by severe sidewall damage. In conventional fabrication, reducing chip dimensions escalates the surface-to-volume ratio, allowing surface non-radiative recombination to dominate and decimate the external quantum efficiency (EQE). However, leveraging a molecular beam epitaxy (MBE) process to fabricate ultra-small devices alters this scaling trajectory, yielding an inverse relationship where EQE improves as chip dimensions shrink.

Evaluating these MBE-grown devices from over twenty microns down to 3.5 microns square reveals extraordinary optoelectronic performance. At the ultra-small limit of 3.5 microns, the devices achieve a record-high peak EQE of approximately 38%. Furthermore, these emitters exhibit an exceptionally stable efficiency profile under low-injection conditions, maintaining high performance even as current density is scaled down from the peak operating point.

To quantify this low-current stability, a metric defined as the EQE drop at a current density of 0.01 amperes per square centimeter relative to the peak EQE reveals a stark divergence in device physics. While conventional SCP devices suffer from an escalating EQE drop as size decreases due to sidewall defects, the MBE-fabricated emitters exhibit the opposite behavior, with the 3.5-micron device limiting this drop to about 26%. This suppression demonstrates that surface non-radiative recombination has been mitigated to a negligible level compared to bulk recombination.

In this short video, you can learn:
* How MBE fabrication reverses the typical size-dependent EQE degradation in micro-scale optoelectronic devices.
* The quantitative definition of EQE drop used to evaluate device performance at ultra-low current densities.
* Why suppressing surface non-radiative recombination is the key to unlocking highly efficient sub-five-micron microLEDs.

📋 **Clip Abstract** The speaker presents the external quantum efficiency (EQE) performance of microLED devices ranging from 20.5 to 3.5 microns square fabricated via molecular beam epitaxy (MBE). He demonstrates that these MBE devices achieve a record peak EQE of approximately 38% and suppress surface non-radiative recombination at small sizes, contrasting sharply with the severe efficiency drops seen in conventional SCP devices.

🎤 Speaker: Prof. Xuelun Wang
🏢 Company: National Institute of Advanced Industrial Science and Technology (AIST)
📅 Event: AR/VR Connect 2025
📍 Location: Conference Centre, High Tech Campus, Eindhoven, Netherlands

🌐 Learn more at the next TechBlick event: https://www.techblick.com

Is It Possible to Fabricate 200-Nanometer Micro-LEDs with Zero Current Leakage?

Pushing the boundaries of micro-LED scaling into the sub-micron regime introduces severe electrical leakage paths along damaged mesa boundaries. Using electron beam lithography and Neutral Beam Etching (NBE), sub-micron devices with mesa diameters ranging from 1000 nm down to 200 nm were successfully fabricated. Electrical characterization reveals that NBE-processed devices exhibit outstanding insulating properties under reverse bias.

Remarkably, the reverse leakage current at -2.5 V remains below the detection limits of the measurement system, even for the smallest 200 nm devices. This demonstrates that the charge-neutral NBE process prevents the formation of conductive defect paths on the semiconductor surface. In contrast, ICP-etched sub-micron devices are notorious for high leakage currents due to severe lattice damage.

While early sub-micron iterations experienced some p-type contact resistance challenges due to unoptimized contact-hole processing, NBE consistently achieves exceptionally low non-radiative recombination rates across all sub-micron dimensions. This proves NBE's viability for ultra-high-resolution augmented reality (AR) and mixed reality displays.

In this short video, you can learn:
* Fabrication flow of sub-micron GaN micro-LEDs down to 200 nm using electron beam lithography and NBE.
* The elimination of reverse bias leakage currents at -2.5 V using damage-free neutral beam patterning.
* Analysis of non-radiative recombination trends in the sub-micron regime comparing NBE against literature-standard ICP.

📋 **Clip Abstract** This segment explores the scaling limits of GaN micro-LEDs down to 200 nm fabricated with Neutral Beam Etching. The speaker highlights how NBE eliminates current leakage paths under reverse bias, presenting a scalable path for next-generation AR displays.