Size-dependent optical-electrical characteristics of blue GaN/InGaN micro-light-emitting diodes

To derive the impact of chip size reduction on optical efficiency in micro-LED array panels, blue InGaN/GaN LEDs, which consist of 21×7 arrays (60 ppi display) with different mesa sizes on sapphire substrates, are designed and fabricated in this study. Changing the mesa area of the chip is first proposed to investigate the luminous efficiency (cd/A) of the screen. The current efficiency with a peak wavelength of 450 nm reaches up to 14.29 cd/A for the biggest pixel 50µm×60µm and to 12.25 cd/A for the 15µm×25µm chip, delivering high-level efficiencies to the current LED research field. The mechanisms of size-dependent efficiency variation trends and efficiency droops of blue LEDs are investigated experimentally, confirming that the current efficiency is more efficient at high injection current density while exhibiting poorer performance at the low current density region for smaller chips. The peak efficiency corresponds to higher current density with a decrease in chip size according to the carrier recombination ABC model. Moreover, the characteristic curve of the spectrum and the changes in the yellow light band under different incident light conditions (i.e., 355 nm and 375 nm) are analyzed by photoluminescence.