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.

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In this paper, we demonstrate a high-voltage normally-off p-GaN gate high-electron-mobility-transistor (HEMT) to realize the compatible high threshold voltage (VTH) and high drain current (ID) performance. With the optimization of epitaxial structure, VTH is significantly improved in the presented device. Meanwhile, through using the high-quality ALD-Al2O3 passivation layer, the high ID is also realized in the device because of the reduction of the access region resistance. Supported by the device fabrication, the p-GaN gate HEMT delivers a VTH=3.2 V measured by linear extrapolation, a relatively large saturation ID (ID_SAT) of 246 mA/mm, and a high break-down voltage (BV) of 1830 V at 1 mA/mm. Among various p-GaN gate HEMTs with the ID_SAT over 200 mA/mm, the fabricated device has a competitive VTH. The results suggest that the pro-posed p-GaN gate HEMT could be a promising candidate in high VTH and ID power electronics.

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