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Luminescence from GaN-based blue light-emitting diodes grown on grooved sapphire substrates was investigated using cathodoluminescence (CL) and electroluminescence (EL). The 60-nm-deep 2 (ridge) ×4 μm (trench) grooves along the <101~0> direction were created by BCl3-Cl2-based inductively coupled plasma reactive ion etching. Stronger CL and EL from the trench regions of the grooves in GaN and InGaN-GaN multiquantum-wells were observed, confirming its better crystalline quality over the trench regions, further supported by the EL mapping results. Epitaxial lateral growth was believed to initiate from the ridge regions to cover the trench regions at the foremost stage of GaN growth that is similar to the coalescence of islands.