Ultra-small size (1–20 μ m) blue and green micro-LEDs fabricated by laser direct writing lithography

Ultra-small micro-LEDs are essential for next-generation display technology. However, micro-LEDs below 5 μm have been seldom reported. In this work, we demonstrate InGaN-based blue and green micro-LEDs from 1 to 20 μm by using laser direct writing lithography. The 1-μm blue micro-LEDs show a peak external quantum efficiency of 13.02%, which is 9.57% for green ones. By characterizing the size-dependent external quantum efficiency and simply assuming that this variety is dominantly determined by the dry-etching induced dead zone, we deduce that the dead zone sizes of carrier injection at the edge of chips are 0.18 and 0.15 μm in blue and green ones, respectively. A time-resolved photoluminescence measurement also shows that carrier lifetime reduction at the edge of blue ones is more serious than that of green ones, reflecting the easier carrier lateral diffusion in the former than the latter. These results exhibit the ability of laser direct writing lithography on micro-LED fabrication and also provide a reference for predicting the limit of their chip size scaling-down.