Fig. 1. (Color online) (a) 3D perspective view for SACM Ge-on-Si APD; (b) top-down perspective of the mask layout in the fabrication process for the device.

Fig. 2. (Color online) The main steps for waveguide-coupled lateral SACM Ge-on-Si APD. (a) Etching waveguides and gratings on the top 220 nm Si layer; (b) five steps of ion implantation; (c) open the Ge window; (d) growth and smooth of germanium layer; (e) M1 finished; (f) M2 finished and annealing.

Fig. 3. (a) SEM image of waveguide; (b) overall SEM plot of a grating; (c) SEM image of further enlarge of grating.

Fig. 4. (Color online) Focused ion beam (FIB) view of the device’s structure.

Fig. 5. (Color online) Measured the dark and photo current I−V curves with input optical powers varying.

Fig. 6. (Color online) (a) Calculated responsivity with the input optical power of −10, −15, −20, −25 dBm; (b) calculated multiplication gain with the input optical power of −10, −15, −20, −25 dBm.

Fig. 7. (Color online) Frequency responses with bias voltages varying from 18 to 21 V, (a) the optical power of −10 dBm, (b) the optical power of −15 dBm, (c) the optical power of −20 dBm, (d) measured 3 dB bandwidth under different optical powers at the bias voltage varying from 10 to 21 V from small signal measurements.

Fig. 8. (Color online) The equivalent circuit of the present waveguide SCAM APD.

Fig. 9. (Color online) Schematic of the experimental setup for the measurement of eye diagrams. The gray and red lines represent the optical and electrical paths, respectively.

Fig. 10. Experimental eye diagrams of the device at the bias voltage of 21 V. (a) At a 20 Gbps with the input optical power of −9 dBm; (b) at a 10 Gbps with input optical power of −9 dBm.