Nonpolar a-plane AlGaN epi-layers were grown on a semi-polar r-plane sapphire substrate with an innovative two-way pulsed-flows metal organic chemical vapor deposition growth technology. A root-mean-square value of 1.79 nm was achieved, and the relative light transmittance of the a-plane AlGaN epi-layer was enhanced by 36.9%. These results reveal that the innovative growth method is able to improve the surface morphology and reduce the defect density in nonpolar a-plane Al _x Ga_{1– x} N epi-layers, particularly those with an Al composition greater than 0.5, which are key materials for the fabrication of nonpolar AlGaN-based high light emission efficiency deep-ultraviolet light-emitting diodes.

This study demonstrated InGaN-based amber micro-light-emitting diodes (μLEDs) with varying Al contents of 2%, 5%, and 16% in barriers. The μLEDs with Al _0.05 GaN in barriers exhibited the highest on-wafer wall-plug efficiency due to the good material quality and optimal energy band engineering for carrier injection. We fabricated μLEDs with diameters ranging from 60 to 10 μm using the optimal epi-structure. The forward voltage was 2.15 V at 1 A/cm ² , a significantly lower value compared to others. The external quantum efficiency and wall-plug efficiency of the packaged μLEDs with a diameter of 10 μm are 4.8% and 4% at 1 A/cm ² , respectively. The slight decrease in efficiency of 10-μm μLEDs can be attributed to the sidewall effect, which was confirmed by photoluminescent and lifetime mapping.

The structural and optical properties for a nonpolar GaN epilayer grown with an in situ SiN _x interlayer was studied intensively. The superficial defects were decreased by 83% and root-mean-square was reduced by 61% for nonpolar GaN with an SiN _x interlayer. The in situ SiN _x was revealed to be powerful to block basal-plane stacking faults (BSFs) in nonpolar GaN because BSF density was reduced from 1.83 × 10 ⁵ to 8.13 × 10 ⁴ cm ⁻¹ and BSF-related emission was remarkably suppressed by the SiN _x interlayer. Moreover, the fast decay lifetime increased from 16.2 to 71.1 ps, which implied the non-radiative recombination in nonpolar GaN was significantly suppressed after the insertion of the SiN _x layer.