Artificially formed resistive ITO/p-GaN junction to suppress the current spreading and decrease the surface recombination for GaN-based micro-light emitting diodes.

ABSTRACT

Due to the increased surface-to-volume ratio, the surface recombination caused by sidewall defects is a key obstacle that limits the external quantum efficiency (EQE) for GaN-based micro-light-emitting diodes (µLEDs). In this work, we propose selectively removing the periphery p+-GaN layer so that the an artificially formed resistive ITO/p-GaN junction can be formed at the mesa edge. Three types of LEDs with different device dimensions of 30 × 30 µm2, 60 × 60 µm2 and 100 × 100 µm2 are investigated, respectively. We find that such resistive ITO/p-GaN junction can effectively prevent the holes from reaching the sidewalls for µLEDs with smaller size. Furthermore, such confinement of injection current also facilitates the hole injection into the active region for µLEDs. Therefore, the surface-defect-caused nonradiative recombination in the edge of mesa can be suppressed. Meantime, a reduction of current leakage caused by the sidewall defects can also be obtained. As a result, the measured and calculated external quantum efficiency (EQE) and optical output power for the proposed LED with small sizes are increased.