A plurality of III-nitride semiconductor structures, each including a light emitting layer disposed between an n-type region and a p-type region, are grown on a composite substrate. The composite substrate includes a plurality of islands of III-nitride material connected to a host by a bonding layer. The plurality of III-nitride semiconductor structures are grown on the III-nitride islands. The composite substrate may be formed such that each island of III-nitride material is at least partially relaxed. As a result, the light emitting layer of each semiconductor structure has an a-lattice constant greater than 3.19 angstroms.