Self-assembled GaN nanocolumns were grown on sapphire and Si substrates by rf-plasma-assisted molecular-beam-epitaxy, clarifying the growth condition. The nanocolumn crystal showed a highly efficient photoluminescence (PL) emission at the room temperature, which intensity was 4 times stronger than that of a high-quality GaN substrate. InGaN/GaN quantum-disk nanocolumn LEDs were fabricated on n-type (111) Si substrates. For a macroscopic emission area of 500-&mgr;m-diameter, a broad electro-luminescence (EL) emission spectrum extending from the blue to the red region was observed. Microscopic EL measurement was performed for a 3-&mgr;m-diameter detection area, demonstrating a drastic spectral narrowing. In the microscopic EL spectrum, no blue shift of the emission wavelength was observed when the injection current increased. This suggests that the carrier localization or/and the piezo-electric field is minimized in nanocolumns. Selective growth of GaN nanocolumns was performed by use of patterned pre-deposited Al layers.