Fig. 1. (a) Three-dimensional schematic diagram of the SACM APD. (b) Cross-section schematic diagram of the SACM APD. Standard silicon-on-insulator (SOI) with 220 nm top silicon and 2 μm buried oxide used as substrates. The 300 nm wide P doping is designed as a charge region, and the intrinsic silicon is designed as a multiplication region with width of Wi. The heavily doped N++ and P++ regions located in both sides of the silicon slab serve as connection regions. These regions are connected to the Al electrode through tungsten (W) vias. A 600  nm×260  nm germanium acts as absorption region. Inset, simulated electric field profile of the fundamental TE-polarized optical mode at 1950 nm wavelength at the Ge layer.

Fig. 2. (a) Simulated electric field distribution at the central vertical cross section of device A with −29  V bias. (b) Simulated electric field distribution at the central vertical cross section of device B with −22  V bias. (c) Electric field distribution along the cutline of (a) and (b).

Fig. 3. Static measurements of designed SACM APD at 1950 nm with 0 dBm input power. The blue line represents the measured results of the device A, and the red line represents the measured results of device B. (a) Measured I-V characteristics. The dashed line represents the dark current, and the solid line represents the illuminated current. (b) Measured responsivity as a function of bias voltage. (c) Measured gain as a function of bias voltage. (d) Measured responsivity of the SACM APD versus input wavelength from 1480–1640 nm to 1950–2045 nm. The bias voltages of devices A and B are −29  V and −22  V, respectively. At a wavelength range of 1480–1640 nm, the input power is −18  dBm; at 1950–2045 nm, the input power is 0 dBm.

Fig. 4. Experimental setup of measuring bandwidth and eye diagrams. The solid blue line represents the optical connection, while the dotted dark line represents the electrical connection. Inset, top-view microscope image of the fabricated device.

Fig. 5. (a) Equivalent circuit for cross section view of the SACM APD. (b) Equivalent circuit for top view of the SACM APD. (c) Equivalent circuit of the SACM APD. The blue area represents the SACM APD waveguide region, yellow represents the electrode section, and orange represents the load part.

Fig. 6. Simulated normalized S21 response versus frequency under different bias voltages for devices (a) A and (b) B.

Fig. 7. (a) Measured normalized frequency response for both devices. The blue line represents the measured frequency response of device A at −29  V bias, and the red line represents the measured frequency response of device B at −22  V bias. Measured NRZ-OOK eye diagram of device A at bit rates of (b) 12 Gbit/s and (c) 16 Gbit/s. Measured NRZ-OOK eye diagram of device B at bit rates of (d) 16 Gbit/s and (e) 20 Gbit/s.

Fig. 8. 3 dB bandwidth and GBP versus avalanche multiplication gain for devices (a) A and (b) B.