Fig. 1. Development of Micro-LED

Fig. 2. Partial reflection propagation paths of light in optical microcavity (don't considering refraction phenomenon caused by difference in refractive index)

Fig. 3. Red, green, and blue Micro-LED angular emission distributions at different sizes^[39]. (a) Red light; (b) green and blue lights

Fig. 4. Combination of tilted structure and black matrix structure to alleviate color shift^[26]. (a) Structure of Micro-LED array; (b) total emission, top emission, and sidewall emission of red, green, and blue Micro-LEDs at different angles; (c) changes in the light intensity enhancement ratio of each color with the variation of the inclination angle at the bottom of Micro-LED; (d) angular emission distributions of different colors at different azimuth angles; (e) angular color shifts of 10 reference colors in the RGB Micro-LED display system when viewing angle is 0°‒80°

Fig. 5. Ag reflective layer structure with patterned conical structure^[42]. (a) Structure of blue Micro-LED; (b) variation in angular distribution of luminescence intensity and light extraction efficiency of blue Micro-LED with cone height; (c) angular distribution and parameters of the luminescence intensity of red, green, and blue Micro-LEDs that comply with Lambert's cosine law; (d) angular color shifts of 10 reference colors in the RGB Micro-LED display system when viewing angle is 10°‒90°; (e) angular color shift values of 7 corresponding colors when viewing angle is 10°‒90°

Fig. 6. Improved DBR structures^[45]. (a) Schematic diagram of the effect by improved DBR on red Micro-LED; (b) conventional DBR structure, the 1st improved DBR structure, and the 2nd improved DBR structure; (c) changes in EL spectra of different DBR structures under different current densities; (d) color shifts of red Micro-LED with different DBRs

Fig. 7. Improvement principle of RCPEF color purity^[51]