The long-wavelength photonic device comprises an active region that includes at least one quantum-well layer of a quantum-well layer material that comprises InyGa1-yAsSb in which y≧0, and that additionally includes a corresponding number of barrier layers each of a barrier layer material that includes gallium and phosphorus. The barrier layer material has a conduction-band energy level greater than the conduction-band energy level of the quantum-well layer material and has a valence-band energy level less than the valence-band energy level of the quantum-well layer material.