Non-Polar GaN Micro-Crystal Array for High-Efficiency Light-Emitting Diodes

GaN-based micro light-emitting diodes (µ-LEDs) have been considered next-generation displays, given the stable operation for a long time and red, green, and blue light emissions through control of the GaN/InGaN structure and composition. However, GaN nano/micro rod crystals grown in the c-axis ([0001]) direction have physical limitations in luminous efficiency due to spontaneous and piezoelectric polarizations. In this work, we employed the epitaxial growth of non-polar GaN nano/micro crystals in the m-axis ([1-100]) direction. The key to the vertically exposed m-axis GaN relies on the precise rearrangement of the ZnO crystals via shear force. We confirmed that most ZnO crystals over a cm-scale wafer were uniformly re-aligned along the shearing direction. Then, the growth of non-polar GaN crystals and subsequent epi-growth (InGaN/GaN MQW, p-type GaN) were performed in turn. Optical and electroluminescence characterizations showed the enhanced luminous efficiency compared with polar crystals, suggesting that our approach can overcome the performance limitations of c-GaN crystals.