High-index low-loss gallium phosphide thin films fabricated by radio frequency magnetron sputtering

High-index low-loss Gallium Phosphide thin films for visible light have been produced by radio frequency magnetron sputtering in an argon environment. This broadens the high refractive index limit of transparent optical materials using a physical deposition process. Energy-dispersive x-ray analysis and spectroscopic ellipsometry were used to characterize the stoichiometry and optical properties. A post-deposition high-temperature anneal was found to be necessary to restore the proper stoichiometric ratio and to reduce the absorption. The annealing conditions were optimized by an in-situ fiber-optic transmission spectrum monitoring system. The films exhibit a high refractive index (N = 3.23) and a low extinction coefficient (K = 0.029) at 633 nm. Such high index GaP films have broad applications in nanophotonic device designs.