Enhancing microstructure and device performance of InGaN quantum dot micro-LEDs through substrate off-cut angle modulation.

InGaN quantum dots (QDs) are regarded as a compelling candidate material for the fabrication of high-quality GaN-based micro-LEDs. In this work, to study the impact of a substrate structure on InGaN QDs and QD-based micro-LEDs, GaN-on-sapphire substrates with off-cut angles toward the a-axis of 0.2°, 0.4°, and 0.7° were utilized as templates for the fabrication of InGaN QDs and InGaN QDs-based micro-LEDs. Experimental results show that GaN template with 0.4° off-cut angle exhibits the narrowest terrace width and enables InGaN QDs to be higher and more uniform. The InGaN QD sample grown on 0.4° substrate has a very small wavelength shift of 2.5 nm with temperature increasing and owns the longest photoluminescence peak wavelength implying the highest In content. Furthermore, electroluminescence (EL) spectra demonstrate that QD-based micro-LED array has excellent wavelength stability under various injection currents, and the stability can be improved further on a GaN template with narrower terraces. The results indicate that altering the terrace width of GaN template is a feasible scheme for improving the properties of GaN-based micro-LEDs.

Investigation on the Optical Properties of Micro-LEDs Based on InGaN Quantum Dots Grown by Molecular Beam Epitaxy.

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.