Fig. 1. Normally incident Ge/Si PD. (a)(b) Cross-sectional view of normally incident Ge/Si PD and its 3 dB bandwidth^[23]; (c)(d) schematic diagram of Ge/Si PD with integrated optical resonator structure and its bandwidth^[25]

Fig. 2. High-speed VPIN Ge/Si PD^[13].(a) Schematic diagram; (b) cross-sectional diagram; (c) cross-sectional scanning electron microscopy (SEM) image of Ge/Si PD; (d) bandwidth test results

Fig. 3. High-speed LPIN Ge/Si PD^[29]. (a) Schematic diagram; (b) top view optical microscope image, (c) cross-sectional scanning electron microscope image (perpendicular to waveguide direction); (d) bandwidth measurement result

Fig. 4. Equivalent model of germanium-silicon detectors and ideal bandwidth. (a) Schematic diagram structure of simplified equivalent RC circuit of Ge PIN PD; (b) relationship between transmission time limit, RC limit and total 3 dB bandwidth of Ge PIN PD and width of essential region

Fig. 5. Simplified equivalent circuit of a gain peaking Ge/Si PD with on/off chip inductor

Fig. 6. High-speed Ge/Si PD with LPIN structure. (a) Cross-sectional schematic of LPIN Ge/Si PD^[27]; (b) transmission electron microscopy (TEM) images^[27]; (c) 3 dB bandwidths measured under various bias voltages (A, B, and C correspond to intrinsic regions with widths of 0.5, 0.7, and 1.0 μm, respectively)^[27]; (d) scanning transmission electron microscopy (STEM) images^[12]; (e) energy-dispersive X-ray spectroscopy (EDX) mappings^[12]; (f) bandwidth measurement results^[12]

Fig. 7. Gain peaking VPIN Ge/Si PD. (a)(b) Microscope image of gain peaking Ge/Si PD with on-chip double layer spiral inductor, and its measured S21 curves^[46]; (c)(d) schematic image of gain peaking Ge/Si PD with off-chip inductor and its measured bandwidth^[36]; (e)(f) microscope image of gain peaking Ge/Si PD with optimized inductor design and its measured bandwidth^[39]

Fig. 8. Relationship between dark current density and bandwidth of Ge/Si PD (the numbers correspond to the reference numbers)

Fig. 9. Relationship between responsivity and bandwidth of Ge/Si PD (the numbers correspond to the reference numbers)

Fig. 10. Applications of high-speed Ge/Si PD. (a) 3D integrated optoelectronic transceiver^[78]; (b)(c) experimental feedback, control loop, and system schematic diagram^[79]; (d) schematic diagram of amplifier-free wireless communication system^[80]