High-Efficiency Deep Ultraviolet Light-Emitting Diode Based on Ag-Nanodot/Pd/Al Composite Electrode

The light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet light-emitting diodes (DUV LEDs) is severely constrained by the strong ultraviolet (UV) absorption of the p-GaN contact layer and the low reflectivity of the p-type electrode to UV light. In this work, Ag-nanodot (AgND)/Pd/Al composite electrodes with varying coverage ratios were fabricated via an Ag–Pd displacement reaction on the 8-nm-thick p-GaN surface to enhance the overall reflectivity of the electrode. The feasibility of the Ag–Pd displacement reaction was confirmed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) analyses. Three-dimensional finite-difference time-domain (3D-FDTD) simulations and reflectivity measurements on sapphire substrates consistently demonstrate that reducing the coverage ratio of AgND/Pd effectively improves electrode reflectivity. At a driving current of 40 mA, the light output power (LOP) and wall-plug efficiency (WPE) of DUV LEDs fabricated with AgNDs/Pd/Al electrodes (coverage ratio: 18.9%) are increased by 89% and 65.8%, respectively, compared with those using fully covered Ag/Pd/Al electrodes. The results of this study highlight the key role of p-electrode reflectivity in achieving high-efficiency DUV LEDs and provide a feasible technical route for improving the LEE of DUV LEDs.