On the mechanism of carrier recombination in downsized blue micro-LEDs

The mechanism of carrier recombination in downsized mu-LED chips from 100 x 100 to 10 x 10 mu m(2) on emission performance was systemically investigated. All photolithography processes for defining the mu-LED pattern were achieved by using a laser direct writing technique. This maskless technology achieved the glass-mask-free process, which not only can improve the exposure accuracy but also save the development time. The multi-functional SiO2 film as a passivation layer successfully reduced the leakage current density of mu-LED chips compared with the mu-LED chips without passivation layer. As decreasing the chip size to 10 x 10 mu m(2), the smallest chip size exhibited the highest ideality factor, which indicated the main carrier recombination at the high-defect-density zone in mu-LED chip leading to the decreased emission performance. The blue-shift phenomenon in the electroluminescence spectrum with decreasing the mu-LED chip size was due to the carrier screening effect and the band filling effect. The 10 x 10 mu m(2) mu-LED chip exhibited high EQE values in the high current density region with a less efficiency droop, and the max-EQE value was 18.8%. The luminance of 96 x 48 mu-LED array with the chip size of 20 x 20 mu m(2) exhibited a high value of 516 nits at the voltage of 3 V.