Lateral Carrier Diffusion in Ion-Implanted Ultra-Small Blue III-Nitride MicroLEDs

Ultrasmall micro-light-emitting diodes (μLEDs), sized below 10 μm, are indispensable to create the next-generation augmented and virtual reality (AR/VR) devices. Their high brightness and low power consumption could not only enhance the user experience by providing vivid and lifelike visuals but also extend device longevity. However, a notable challenge emerges: a decrease in efficiency with a reduced size. This study casts light on this critical issue by investigating the lateral carrier diffusion in ion-implanted μLEDs. The implanted area restricts the carrier injection and defines the μLED size to diameters of 10, 5, and 2 μm without introduction of nonradiative recombination centers in the quantum well area. We observed a drop of efficiency for smaller devices, similar to the case of conventional μLEDs with etched sidewalls. Electroluminescence of μLEDs was studied using a Gaussian beam telescope to analyze light intensity profiles and hence the spatial carrier distribution within the active region of μLEDs. Lateral diffusion length was determined to be 11.2 μm at j = 1 A/cm² and decreased down to 2.4 μm for j = 1000 A/cm². We explain the underlying mechanism behind the size-dependent efficiency observed in μLEDs, attributed to lateral carrier diffusion.