A polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure to improve the hole injection for GaN based micro-LED with secondary etched mesa

A low hole injection efficiency for InGaN/GaN micro-light-emitting diodes(μLEDs) has become one of the main bottlenecks affecting the improvement of the external quantum efficiency(EQE) and the optical power. In this work, we propose and fabricate a polarization mismatched p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure for 445 nm GaN-based μLEDs with the size of 40 × 40 μm^(2), which serves as the hole injection layer. The polarization-induced electric field in the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure provides holes with more energy and can facilitate the non-equilibrium holes to transport into the active region for radiative recombination. Meanwhile, a secondary etched mesa for μLEDs is also designed, which can effectively keep the holes apart from the defected region of the mesa sidewalls, and the surface nonradiative recombination can be suppressed. Therefore, the proposed μLED with the secondary etched mesa and the p-GaN/p-Al_(0.25)Ga_(0.75)N/p-GaN structure has the enhanced EQE and the improved optical power density when compared with the μLED without such designs.