Fig. 1. Typical epitaxial structure diagram of DUV LED devices

Fig. 2. (a) Size-dependent I–V characteristics curves; (b) Size dependence of current density under the same voltage^[44]; (c) LEDs A, B, C with sidewall damages (The usable area ratios for LEDs A, B and C are 85%, 75% and 36%^[45])

Fig. 3. Relationship between light extraction efficiency and size of TM polarized light simulated in FDTD

Fig. 4. (a) Light output power as a function of injection current for the DUV LEDs with different mesa sizes; (b) Size dependence of optical power density^[44] ; (c) Light output power and (d) the LEE enhancement factor of the DUV LEDs at different currents for the three investigated devices^[52]

Fig. 5. (a) Structure diagram of deep ultraviolet LED with meshed p-GaN; (b) LEEs for DUV LED with the meshed p-GaN contacts as a function of the spacing of nanorods; (c) Relationship between LEE and nanorod spacing of DUV LEDs with meshed p-GaN and truncated p-AlGaN contacts^[59]; (d) Schematics of the mesh p-GaN/ITO DUV LED; (e) Measured L–I characteristics and I–V characteristics of the two kinds of DUV LEDs^[60]

Fig. 6. (a) Schematic cross-sectional view of reference device, Device 1 and Device 2; (b) Current-voltage characteristics for reference device, Devices 1 and Device 2^[64]

Fig. 7. (a) Structure diagram of DUV LED with n-AlGaN nanostructure array on Ga surface; (b) TE polarized XY cross section electric field distribution of traditional device (left) and surface finish Ga plane n-AlGaN device (right)^[67]

Fig. 8. Schematic of (a) the Ref. DUV LEDs and (b) CSG DUV LEDs ^[74]; (c) Schematic diagram and SEM image of device structure with inclined and vertical sidewalls; (d) Output power density under different current densities for 20 µm-diameter LEDs (solid lines) and 40 µm-diameter LEDs (dashed-dotted lines) with vertical and inclined sidewalls^[75]

Fig. 9. (a) Four difference structures DUV LEDs; the XY cross section electric field profile of TM-polarized light for (b) Device 1; (c) Device 2; (d) Device 3 ^[79]

Fig. 10. (a) Schematic of the various ODR devices in cross-section view; (b) Enhancement factors for LEE, voltage, and WPE of various ODRs ^[80]

Fig. 11. (a) Schematic diagrams for MIS-structured DUV LED, i.e., Device A; Calculated energy band diagrams of (b) n-AlGaN layer and n-electrode metal for Device R; (c) n-AlGaN layer, insulator, and n-electrode metal for Device A^[84]