Diffusing the photon-assisted regenerated holes to increase the WPE for 259 nm AlGaN-based DUV LEDs with three-dimensional n-ZnO/p-AlGaN photon-sensitive micro-structure arrays

In this work, we have proposed and fabricated 259 nm AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) with three-dimensional (3D) n-ZnO/p-AlGaN micro-structure arrays. The 3D n-ZnO/p-AlGaN micro-structures are formed by filling n-ZnO micro-pillars into the cylindrical grooves in the p-AlGaN layer. The n-ZnO/p-AlGaN micro-structures can absorb the 259 nm unextracted ultraviolet photons, and the reversely biased n-ZnO/p-AlGaN junction arrays regenerate carriers. The excellent charge-coupling effect in the purposely designed 3D n-ZnO/p-AlGaN structures enables the hole drift and diffusion into the p-AlGaN region, which on the one hand suppresses the hole depletion effect on the p-AlGaN layer surface for reducing the p-type contact resistance, and on the other hand, the hole injection into the active region is more favored. As a result, the forward voltage is decreased by 25% at the 45 mA injection current, and the optical power is improved by 47% for the proposed device. This results in the increased wall-plug efficiency by 46% for the 259 nm AlGaN-based DUV LEDs.