Bulk relaxed Wurtzite In-containing III-nitride layers having a smooth and substantially pit-free surface morphology and an interface region having a substantially relaxed in-plane a-lattice parameter and characterized by a single-phase gallium-polar (0001) orientation are disclosed. Methods of making the bulk relaxed Wurtzite In-containing III-nitride layers using MOCVD growth conditions are also disclosed. Semiconductor structures include epitaxial layers grown on a bulk relaxed Wurtzite In-containing III-nitride layer. The semiconductor structures can be used in optoelectronic devices such as in light sources for illumination and display applications.