Graphene-on-silicon nitride waveguide photodetector with interdigital contacts

Graphene photodetectors have attracted research attention because of their potential high speed and broad spectral bandwidth. However, their low responsivity and quantum efficiency compared with germanium or III-V material based photodetectors limit their practical use. Here, we demonstrate a chemical vapor deposited graphene photodetector integrated on a silicon nitride. Interdigital metal contacts are used to reduce the channel spacing down to ∼200 nm. At zero bias, a metal-graphene junction is used for photodetection, which is beneficial for an electro-optic bandwidth of ∼33 GHz in the 1550 nm wavelength band. At a bias of 1 V, a photoconductive responsivity of ∼2.36 A/W at 1550 nm was observed. The high speed and high responsivity make the device promising for photodetection in the telecommunication C-band. A diffusion model is applied to study the carrier transition process in the graphene channel. By adopting this model, the high performance of the device is explained. The main limitation in the responsivity of graphene photodetectors is also analyzed.