A novel infrared photodiode based on a graphene/
n-type silicon heterojunction is explored. The heterojunction photodiode of interest has a large Schottky barrier that results in a low dark current. Graphene serves as the absorbing medium at a wavelength for which silicon is transparent. Under infrared illumination, photo-excited electrons in the graphene gain energy and thus have a greater probability to overcome the barrier and contribute to the photocurrent. We have demonstrated photodiode operation of a graphene/ n-Si heterojunction at 1.3 and 1.55 μm wavelength, with 14% internal quantum efficiency and 1.5 pW/Hz1/2 noise-equivalent power, for potential use in silicon photonics.