In this work, we investigate the use of nanoscale polarization engineering to achieve efficient hole injection from metals to ultra-wide bandgap AlGaN, and we show that UV-reflective aluminum (Al) layers can be used for hole injection into p-AlGaN. The dependence of tunneling on the work function of the metal was investigated, and it was found that highly reflective Al metal layers can enable efficient hole injection into p-AlGaN, despite the relatively low work function of Al. Efficient tunneling hole injection was confirmed by light emission at 326 nm with an on-wafer peak external quantum efficiency and a wall-plug efficiency of 2.43% and 1.33%, respectively. A high power density of 79.0 W/cm(2) was measured at 1200 A/cm(2). The metal/semiconductor tunnel junction structure demonstrated here could provide significant advantages for efficient and manufacturable device topologies for high power UV emitters. Published by AIP Publishing.