Minimizing interface defects and enhancing optical brightness of µLEDs through polymeric encapsulants

The need for high resolution microLED (µLED) arrays, for applications in chip-level optical interconnects and augmented/virtual reality displays, requires the continuing miniaturization of the LED to reduce the pixel size and enable high pixel density. This miniaturisation degrades the µLED optical brightness due to non-radiative recombination from side-wall defects as the surface-to- volume ratio increases with decreasing µLED size. In this investigation, we demonstrated a fabrication approach combining dry and wet etching processes with polymeric passivation layers, to construct InGaN-based µLEDs that showed negligible degradation due to sidewall effects for devices having diameters as small as 6 µm. The µLEDs exhibited extremely low surface-recombination velocities (<10 cm/s) and high wall plug efficiencies, 𝜂 _WPE , of 20.3 % at a current density of 2.5 A/cm ² with an optical power density of 1.4 W/cm ² . A simple model was developed to explain the dependence of the µLED performance as a function of the µLED geometry. The model identified the minimum µLED size at which surface-driven degradation becomes dominant and informed the development and demonstration of a fabrication method that reduces these scaling effects in high-resolution displays.