Fig. 1. (a) Structural diagram of three-terminal Ge-on-Si APD. (b) SEM image of pixel units. (c) Electric field simulation diagram of Ge region. (d) Simulated electric field in Si APD area [electric field at different positions of line A in (b)].

Fig. 2. (a) Current characteristic diagram at 1550 nm under different input optical power. (b) Responsivity characteristic diagram at 1550 nm under different input optical power. (c) Current characteristic diagram at 1310 nm under different input optical power. (d) Responsivity characteristic diagram at 1310 nm under different input optical power. The figure shows the voltage applied to two terminals Ge and n++ Si.

Fig. 3. It represents the simulated dark current diagram (current output at the n++ terminal) when different fixed voltages are applied to Ge when the n++ Si voltage is 60 V and p++ Si is grounded.

Fig. 4. When the n++ Si terminal scanning voltage is 60 V, the p++ Si terminal is grounding, and different fixed voltages are applied to Ge: (a) dark current; (b) current characteristic diagram at 1550 nm under input optical power −20  dBm. (c) Under the fixed Si voltage, the dark current of n++ Si terminal varies with the applied voltage of Ge. (d) Under the fixed Si voltage, the current at 1550 nm at an input optical power of −20  dBm varies with the applied voltage of Ge.

Fig. 5. (a) Schematic diagram of three-terminal APD. (b) Y direction electric field simulation in Si region [position from B to B′ in (a)]. (c) X direction electric field simulation of Si charge region [position from A to A′ in (a)]. (d) Electric field simulation diagram of Ge region.

Fig. 6. (a) Photocurrent diagram at 10−7  A. (b) Responsivity at 10−7  A. (c) Photocurrent diagram at 10−8  A. (d) Responsivity at 10−8  A.

Fig. 7. When the voltage on Ge is −27.5  V. (a) Current characteristic diagram at 1310 nm under different input optical power. (b) Responsivity characteristic diagram at 1310 nm under different input optical power. (c) Current characteristic diagram at 1550 nm under different input optical power. (d) Responsivity characteristic diagram at 1550 nm under different input optical power.

Fig. 8. When the voltage on Ge is −27.5  V. (a) Avalanche gain at 1310 nm wavelength. (b) Avalanche gain at 1550 nm wavelength.

Fig. 9. When the applied voltage on p++ Ge is −27.5  V and the input optical power is −20  dBm. (a) Responsivity in O-band. (b) Responsivity in C-band (1530–1560 nm) and L-band (1570–1600 nm).

Fig. 10. (a) Current at −20  V on Ge. (b) Current at −25  V on Ge. (c) Current at −30  V on Ge. (d) At different voltages on Ge, the photocurrent is greater than the multiple of dark current.

Fig. 11. (a) The APD has a normalized RF response characteristic at a voltage of Ge at −27.5  V and different Si input voltages. (b) The APD voltage on the Ge is −27.5  V, and the S22 parameters are measured under different Si input voltages. (c) The APD has a normalized RF response characteristic at a voltage of Si at 15 V and different Ge input voltages. (d) The APD voltage on the Si is 15 V, and the S22 parameters are measured under different Ge input voltages [the specific voltage values are shown in (c)].

Fig. 12. (a) When the voltage is −27.5  V on Ge, the three-terminal APD equivalent circuit model. (b) When the signal ends are input to 15 V, the reflection coefficient is measured and fitted. (c) The relative error values between simulation and practice in (b).