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In this study, the growth behavior of Indium gallium nitride (InGaN)-based nanocolumn arrays was investigated, and red emission nanocolumn micro-light emitting diodes (μ-LEDs) were fabricated. The internal structure of the InGaN/GaN superlattice (SL) layer under the multiple-quantum-well (MQW) active layers was evaluated using high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) analysis. It was revealed that the InGaN crystal plane at the top of the nanocolumn changed from the c-plane, (1-102) plane, to the (10-11) plane as the number of SL pairs increased. A semipolar (10-11) plane was completely formed on top of the nanocolumn by growing InGaN/GaN SLs over 15–20 pairs, where the InGaN/GaN SL layers were uniformly piled up, maintaining the (10-11) plane. Therefore, when InGaN/AlGaN MQWs were grown on the (10-11) plane InGaN/GaN SL layer, the growth of the (10-11) plane semipolar InGaN active layers was observed in the HAADF-STEM image. Moreover, the acute nanocolumn top of the (10-11) plane of the InGaN/GaN SL underlayer did not contribute to the formation of the c-plane InGaN core region. Red nanocolumn μ-LEDs with an φ12 µm emission window were fabricated using the (10-11) plane MQWs to obtain the external quantum efficiency (EQE) of 1.01 % at 51 A/cm2. The process of nanocolumn μ-LEDs suitable for the smaller emission windows was provided, where the flat p-GaN contact layer contributed to forming a fine emission window of φ5 µm.

In this study, we demonstrated a GaN surface contamination and cleaning technique focused on O- and Si-based compounds generated by an exposure to the atmosphere. The GaN single-crystalline layers were grown on sapphire (0001) substrates using the ultra-high-vacuum radio-frequency sputter epitaxy technique. During X-ray photoelectron spectroscopy (XPS) measurements, O1s and Si2p XPS signals were detected on the as-grown GaN layer surface. Thermal treatment was performed in order to remove these impurities, and the results of the XPS measurements indicated a significant decrease in the O–Ga bonds on the GaN layer surface. Following the buffered hydrogen fluoride etching treatment, a decrease in the Si compounds on the GaN layer surface was confirmed by a significant decrease in the Si2p/Ga3d XPS signal intensity ratio.