InGaN quantum dots (QDs) have attracted significant attention as a promising material for high-efficiency micro-LEDs. In this study, plasma-assisted molecular beam epitaxy (PA-MBE) was used to grow self-assembled InGaN QDs for the fabrication of green micro-LEDs. The InGaN QDs exhibited a high density of over 3.0 × 10¹⁰ cm⁻², along with good dispersion and uniform size distribution. Micro-LEDs based on QDs with side lengths of the square mesa of 4, 8, 10, and 20 μm were prepared. Attributed to the shielding effect of QDs on the polarized field, luminescence tests indicated that InGaN QDs micro-LEDs exhibited excellent wavelength stability with increasing injection current density. The micro-LEDs with a side length of 8 μm showed a shift of 16.9 nm in the peak of emission wavelength as the injection current increased from 1 A/cm² to 1000 A/cm². Furthermore, InGaN QDs micro-LEDs maintained good performance stability with decreasing platform size at low current density. The EQE peak of the 8 μm micro-LEDs is 0.42%, which is 91% of the EQE peak of the 20 µm devices. This phenomenon can be attributed to the confinement effect of QDs on carriers, which is significant for the development of full-color micro-LED displays.

Thermal degradation of InGaN quantum dots (QDs) during the temperature ramp for GaN quantum-barrier growth can compromise micro-light-emitting-diode active regions. Five-period InGaN/GaN QD structures with low-temperature-grown GaN (LT-GaN) caps of 0 nm (C0), 2 nm (C2), and 4 nm (C4) were studied. The nominal total GaN quantum barrier was fixed at 10 nm by adjusting the higher-temperature-grown GaN portion to 10, 8, and 6 nm, respectively. The active regions were characterized by high-resolution X-ray diffraction, aberration-corrected transmission electron microscopy, and temperature-dependent photoluminescence; post-ramp surface-reference specimens were examined by atomic force microscopy; and 10 μm × 10 μm micro-LEDs were evaluated by electroluminescence spectroscopy and integrating-sphere external quantum efficiency measurements. Compared with C0 and C2, C4 displayed clearer satellite reflections, more laterally continuous InGaN-rich contrast, and weaker thermal photoluminescence quenching; its surface reference also showed a more continuous terrace-like morphology with fewer fine depressions. The C4 micro-LED reached a peak external quantum efficiency of 4.45% at 20 A cm⁻², compared with 2.58% at 150 A cm⁻² for C0 and 1.80% at 140 A cm⁻² for C2. Together, these results associate more effective thermal protection with a reduced relative contribution from defect-assisted nonradiative recombination and enhanced device efficiency.

Size-dependent efficiency degradation remains a major challenge for deeply scaled GaN-based micro-light-emitting diodes (micro-LEDs) because etched sidewalls increasingly influence carrier recombination. Here, square micro-LEDs with lateral dimensions of 5–50 μm were fabricated from the same plasma-assisted molecular-beam-epitaxy-grown wafer containing a five-period InGaN quantum-well/1 nm Al_0.1Ga_0.9N interlayer/InGaN quantum-dot-like (QW–QD) composite active region. Contrary to the conventional size effect, the light output power density and external quantum efficiency (EQE) increased as the mesa size decreased. The peak EQEs were 3.66%, 4.53%, 5.63%, 7.04%, and 7.27% for the 50, 40, 30, 10, and 5 μm devices, respectively, corresponding to an approximately 98.6% increase from 50 to 5 μm. The favorable scaling is consistent with localization-mediated suppression of lateral carrier loss combined with size-dependent light extraction. The present measurements do not quantitatively separate injection, internal efficiency, and extraction contributions. These results demonstrate the potential of ultrathin-interlayer QW–QD active-region engineering for scaled GaN micro-LEDs.