Circular p-GaN/p-AlGaN Rods With Metal/Thin Dielectric-Type p-Contact to Increase the Wall-Plug Efficiency for 258-nm AlGaN-Based Deep Ultraviolet Light Emitting Diodes

Very strong optical absorption and the poor hole injection efficiency make AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) encounter low external quantum efficiency (EQE) and poor light output power (LOP). To solve these issues, we design and fabricate circular p-GaN/p-AlGaN rods with a metal/thin dielectric-type p-contact for DUV LEDs. We find that the local removal of the p-GaN layer can significantly increase the light extraction efficiency (LEE). However, direct p-type contact on the exposed p-AlGaN layer causes the increased energy band barrier height. Hence, we utilize metal/thin low-k insulator/semiconductor (MIS)-based p-type contact on the p-AlGaN layer to reduce the energy band barrier height. The results show that the MIS structure effectively facilitates intraband tunneling effect and increase the hole injection efficiency. Therefore, the forward voltage is decreased and the wall-plug efficiency (WPE) gets improved. The proposed MIS-based p-type contact also favors the reduce leakage current before the devices are turned on, which is reflected by the reduced ideality factor. By investigating the rod sizes and the gap between the neighboring rods, we also find that the enhanced WPE shall take the tradeoff between the LEE and the hole injection efficiency into account.