An integrated plasmonic refractive index sensor: Al nanohole arrays on Ge PIN photodiodes

Collinear refractive index sensors offer highest sensitivities at smallest device foot-print. Using a complementary metal-oxide-semiconductor compatible process for fabrication paves the way to cheap devices enabling integrated biosensors. We present a vertical Ge PIN photodiode equipped with Al nanohole arrays placed directly on top of the diode. The interaction of plasmonic resonances and thin-film reflection within the PIN layer stack enables sensitivities comparable to Au sensing systems showing FOM* up to 14.