Crack-free, up to 2.8 μm thick GaN-based light emitting diodes were grown by metalorganic chemical vapor deposition on 2-inch Si(111) substrates. Elimination of cracks was achieved by using two ∼12 nm thick low-temperature AlN:Si interlayers for stress reduction. A significant enhancement in optical output power was obtained by an in situ insertion of a SixNy mask. Transmission electron microscopy measurements showed a tenfold reduction in dislocation density to ∼109 cm-2 by the low-temperature AlN and SixNy interlayers, resulting in a significant increase in luminescence intensity. Vertically contacted diodes showed a light output power of 152 μW at a current of 20 mA and a wavelength of 455 nm. Turn-on voltages around 2.8 V and series resistances of 55 Ω were obtained.