Graphene‐Enhanced UV‐C LEDs

Abstract

AbstractLight‐emitting diodes in the UV‐C spectral range (UV‐C LEDs) can potentially replace bulky and toxic mercury lamps in a wide range of applications including sterilization and water purification. Several obstacles still limit the efficiencies of UV‐C LEDs. Devices in flip‐chip geometry suffer from a huge difference in the work functions between the p‐AlGaN and high‐reflective Al mirrors, whereas the absence of UV‐C transparent current spreading layers limits the development of UV‐C LEDs in standard geometry. Here it is demonstrated that transfer‐free graphene implemented directly onto the p‐AlGaN top layer by a plasma enhanced chemical vapor deposition approach enables highly efficient 275 nm UV‐C LEDs in both, flip‐chip and standard geometry. In flip‐chip geometry, the graphene acts as a contact interlayer between the Al‐mirror and the p‐AlGaN enabling an external quantum efficiency (EQE) of 9.5% and a wall‐plug efficiency (WPE) of 5.5% at 8 V. Graphene combined with a ≈1 nm NiOx support layer allows a turn‐on voltage <5 V. In standard geometry graphene acts as a current spreading layer on a length scale up to 1 mm. These top‐emitting devices exhibit a EQE of 2.1% at 8.7 V and a WPE of 1.1%.