Fig. 1. Comparison of performance between AlGaN based deep ultraviolet LED and traditional mercury lamp

Fig. 2. Superlattice p-type doped AlGaN^[12]. (a) Diagram of p-AlGaN superlattice structure grown based on desorption-controlled ultrathin layer epitaxy; (b) schematic diagram of the contrast of p-AlGaN superlattice structure

Fig. 3. 3D superlattice and conventional superlattice p-type doping^[13]. (a) Schematic of 3D superlattice p-type doping; (b) schematic of conventional superlattice p-type doping

Fig. 4. Schematic diagram of p-GaN quantum dots assembled into p-AlGaN layer^[14]

Fig. 5. Schematic diagram of four types of EBL structures. (a) Single layer EBL; (b) composite EBL; (c) gradient EBL; (d) superlattice EBL

Fig. 6. Schematic diagram of AlGaN based deep ultraviolet LED structure and changes in EBL Al composition^[20]

Fig. 7. Schematic diagram of AlGaN based deep ultraviolet LED structure and three types of EBL structures^[22]

Fig. 8. IQE and optical output power schematics of four AlGaN based deep ultraviolet LEDs with different p-EBL structures^[23]. (a) Schematic of IQE; (b) schematic diagram of optical output power

Fig. 9. Schematic diagrams of IQE and radiative complexity of four non-polar a-plane AlGaN based deep ultraviolet LEDs with different p-EBL structures^[24]. (a) Schematic of IQE; (b) schematic of radiative complexity

Fig. 10. Schematic diagram of quantum barrier structures of LED R, A, B, C, and D in the MQW region^[25]

Fig. 11. AFM and SEM images of AlN grown on c-plane sapphire substrate in combination with high-temperature annealing technique^[34]. (a) Sputter-grown AlN; (b) high-temperature annealing-grown AlN; (c) AFM image of high-temperature annealing-grown AlN regrown AlN; (d) SEM image of high-temperature annealing grown AlN regrown AlN

Fig. 12. Schematic diagram of crystal improvement after high temperature annealing of AlN^[35]

Fig. 13. Schematic diagram of AlGaN based deep ultraviolet LED structure and three types of quantum barrier structures^[37]

Fig. 14. Schematic diagram of AlGaN based deep ultraviolet LED structure and four quantum barrier structures^[38]

Fig. 15. Schematic structures and energy bands of AlGaN based deep ultraviolet LED^[40]. (a) Schematic structure of AlGaN-based deep-ultraviolet LED with insertion of a superlattice electron-limiting layer; (b) schematic energy bands without an electron-limiting layer; (c) schematic energy bands with insertion of a 100 nm electron-limiting layer

Fig. 16. Schematic diagram of AlGaN based deep ultraviolet LED structure and two types of quantum barrier structures^[41]

Fig. 17. Schematic diagram of AlGaN based deep ultraviolet LED structure and AQW structure implementation^[42]

Fig. 18. Schematic diagram of AlGaN based deep ultraviolet LED with HHS structure as electrode^[43]

Fig. 19. Distribution of energy band of AlGaN based deep ultraviolet LED with a layer of p-AlGaN inserted in n-AlGaN layer ^[44]

Fig. 20. Schematic diagram of AlGaN based deep ultraviolet LED with traditional and new structures ^[5]

Fig. 21. Schematic diagram of AlGaN based deep ultraviolet LED with Ag nanodots/Al electrode and Ni/Au electrode^[47]

Fig. 22. Structure diagram of AlGaN based deep ultraviolet LED with integrated microlens array on sapphire substrate ^[52]

Fig. 23. Structure diagram of AlGaN based deep ultraviolet LED device with antireflective SiO₂^[54]

Fig. 24. Structure diagram of AlGaN based deep ultraviolet LED device coated with SiO₂ on the surface of sapphire substrate and internally roughened^[55]

Fig. 25. Schematic diagram of transparent, transverse, and LEE of AlGaN based deep ultraviolet LEDs with or without inclined sidewalls and whether n-AlGaN and Al/SiO₂ are flat^[59]

Fig. 26. Structure diagram of AlGaN based deep ultraviolet LED after thermal oxidation^[62]

Fig. 27. Relationship between DOP and compressive strain^[64]