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

Micro light-emitting diodes (mu LEDs) 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 mu LEDs (between 2.5 and 10 mu m 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 mu LEDs below 10 mu m. These results are of high relevance for the design of mu LED arrays and show the need for understanding the evolution of LEE and sidewall nonradiative recombination with LED geometry and size.