Group III-nitride quaternary and pentenary material systems and methods are disclosed for use in semiconductor structures, including laser diodes, transistors, and photodetectors, which reduce or eliminate phase separation and provide increased emission efficiency. In an exemplary embodiment the semiconductor structure includes a first ternary, quaternary or pentenary material layer using an InGaAlNAs material system of a first conduction type formed substantially without phase separation, a quaternary or pentenary material active layer using an InGaAlNAs material system substantially without phase separation, and a third ternary, quaternay or pentenary an InGaAlNAs material system of an opposite conduction type formed substantially without phase separation.