Enhanced Efficiency of InGaN/GaN Quantum-Dot Micro-LEDs Through Low-Temperature GaN Capping

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.