Germanium metal-semiconductor-metal photodetectors evanescently coupled with upper-level silicon oxynitride dielectric waveguides

We demonstrate Ge-on-Si metal-semiconductor-metal (MSM) photodetectors monolithically integrated with silicon oxynitride (SiO_xN_y) waveguides. The waveguide is placed on top of the photodetector and between the metal electrodes, evading the shading effect by metal electrodes, which is typical in surface-illuminated MSM photodetectors. The devices showed responsivity of about 0.45 A/W for 80 μm long devices at 1550 nm. The photodetector with 1.5 μm electrode spacing showed 3 dB bandwidth of 2.0 GHz at −2 V and 2 μA dark current. Further studies suggest that with a modified design the structure is capable of achieving 1 A/W responsivity and greater bandwidth.