Solid State Lighting sources, presently being completely based on the semiconductor material Gallium Nitride, will replace inefficient and environmentally harmful conventional light sources, and therefore contribute significantly to a sustainable energy saving and carbon footprint reduction. In order to further support this transition, white LEDs with higher efficiencies and lower cost per lumen have to be developed. The main strategy of GECCO is based on exploiting the vertical sidewalls of 3-dimensional GaN structures with high aspect ratios, where the p-n-junction region is fabricated along the vertical sidewalls of the 3D structure so that this large area can be used as an active area for light emission. Whereas conventional approaches for light emitting material are planar, our GECCO approach exploits the third dimension and is expected to overcome potentially all of the limitations of present GaN material technology, making substantial progress towards the long term goals mentioned in this call (2020): enhanced overall efficacy of white light emission. We will investigate material related aspects of 3-dimensional (3D) GaN in order to get a good handle on the interesting properties of this new class of material, so that it can be used for highly efficient and cost effective whitelight emission. The overall GECCO project objectives are:1.) achieving full control on the growth of high quality 3D GaN material.2.) achieving full control on doping and growth of ternary compounds (InGaN and AlGaN) on the non-polar sidewalls of 3D GaN structures.3.) extending the 3D approach from GaN cores to InGaN cores, with the goal to bridge the green gap (low efficiency for green quantum wells).4.) implementing novel phosphor materials and concepts for a more efficient, 3-dimensional way of light outcoupling and light conversion, including 3D cooling for better efficiency