Lateral carrier diffusion in ion-implanted ultra-small blue III-nitride microLEDs.

Abstract Ultra-small micro-light emitting diodes (µLEDs), sized below 10 µm, are indispensable to create 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 reduced size. This study casts light on this critical issue, 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 non-radiative recombination centres in the quantum well area. We observed a drop of efficiency for smaller devices, similarly as in the case of conventional µLEDs with etched sidewalls. Electroluminescence of µLEDs was studied using a Gaussian beam telescope to analyse 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, attributing it to lateral carrier diffusion.