Fig. 1. Ge photodetector integrated into a rib silicon-on-insulator waveguide: (a) schematic diagram of the integration of Ge on Si MSM photodetector in SOI Rib waveguide, (b) electric field profile for the fundamental transverse electric (TE) mode in the SOI waveguide (rib width 1µm; height 380 nm and etching depth 70 nm), (c) electric field amplitude in a longitudinal cross section of the photodetector (3D-FDTD calculation). The 95% absorption length is about 4 µm.

Fig. 2. Scanning electron microscope image of the integrated Ge on Si MSM photodetector cross-section: A silicon oxide layer onto the Ge layer defines the electrode spacing D. The thickness of the Ge layer grown on a 50 nm thick silicon layer is about 330 nm. The metal contact is directly deposited on Ge. The BOX thickness is 1µm.

Fig. 3. Dark current variation with operating voltage: The dark current (without any illumination) is measured from -10V to +10V voltage for a 10µm long Ge on Si MSM photodetector.

Fig. 4. Normalized photoresponse of the Ge on Si photodetector integrated in rib SOI waveguide: The response dependences are measured for a 10 µm long Ge on Si MSM integrated photodetector for 0.5V, 2V and 6V bias and 1.55 µm wavelength (a) The photoresponses are recorded on an sampling oscilloscope after femtosecond laser pulse illumination. The corresponding intrinsic response times are about 46 ps, 30 ps and 19 ps, respectively. (b) RF response as a function of frequency is directly measured from 0.1 GHz to 50 GHz. The corresponding bandwidths are about 8.5 GHz, 15.4 GHz and 25GHz, respectively.

Fig. 5. -3dB bandwidth versus bias voltage: The cut-off frequency is determined for bias voltage ranging from 0V to 7V for a 10 µm long Ge on Si MSM integrated photodetector at a wavelength of 1.55 µm from both RF and pulse experiments.