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.

Impact of p-AlGaN/GaN hole injection layer on GaN-based vertical cavity surface emitting laser diodes[Invited]

The hole injection capability is essentially important for GaN-based vertical cavity surface emitting lasers[VCSELs]to enhance the laser power.In this work,we propose GaN-based VCSELs with the p-AlGaN/p-GaN structure as the p-type hole supplier to facilitate the hole injection.The p-AlGaN/p-GaN heterojunction is able to store the electric field and thus can moderately adjust the drift velocity and the kinetic energy for holes,which can improve the thermionic emission proc-ess for holes to travel across the p-type electron blocking layer[p-EBL].Besides,the valence band barrier height in the p-EBL can be reduced as a result of usage of the p-AlGaN layer.Therefore,the better stimulated radiative recombination rate and the increased laser power are obtained,thus enhancing the 3 dB frequency bandwidth.Moreover,we also inves-tigate the impact of the p-AlGaN/p-GaN structure with various AIN compositions in the p-AlGaN layer on the hole injection capabilit,the laser power,and the了dB frequency bandwidth.