The origin of the limited impact of an inclined sidewall Al reflector on the light output power of mid-power deep ultraviolet light-emitting diodes

Abstract In this work, the impact of aluminum (Al) reflector coated on the 20° inclined sidewall on light extraction efficiency (LEE) of mid-power deep ultraviolet light-emitting diodes (DUV LEDs) is systematically investigated. Although theoretical analysis indicates that the Al reflector can effectively reflect photons into the escape cone, experimental results reveal that the light output power (LOP) of DUV LEDs is enhanced by only 4.8% for the DUV LEDs using the Al reflector on inclined sidewall. The limited enhancement can be attributed to the fact that the inclined sidewall Al reflector can only reflect the downward-propagating light into the escape cone. Additionally, the small sidewall-to-total-area ratio in the mid-power DUV LEDs and the significant absorption in p-type layer further reduce the amount of light reaching the inclined sidewall. Therefore, the inclined sidewall Al reflector strategy is not recommended for mid-power DUV LEDs due to its limited effectiveness and high fabrication cost, unless eliminating absorption in the p-type layer or increasing inclined sidewall area are utilized.