Vertically Stacked Photodetector Devices Containing Silicon Nanowires with Engineered Absorption Spectra

We fabricate a vertically stacked photodetector device containing silicon nanowire photodetectors formed above a silicon substrate that also contains a photodetector. The nanowire photodetectors have absorption spectra that exhibit peaks for which light is coupled to a waveguide mode, absorbed, and converted to photocurrent. The substrate photodetector converts the light not absorbed by the nanowires to photocurrent. Responsivities of both photodetectors are measured and compared to the predictions of electromagnetic simulations. This device configuration can be thought of as a silicon photodetector with an integrated filter. The filter has the unusual property of converting absorbed light to photocurrent rather than discarding it.