Fig. 1. Waveguide-coupling configurations: (a) butt coupling and (b) evanescent coupling. PIN junction configuration: (c) lateral and (d) vertical.

Fig. 2. Absorption efficiency and device capacitance for evanescent and butt-coupling configurations, assuming intrinsic region width of 1 μm and Ge height of 350 nm.

Fig. 3. BPM simulation of light absorption in the intrinsic region of a lateral PIN photodiode for a 350 nm thick Ge layer in a 10×10  μm cavity, butt coupled to a Si waveguide (220  nm×500   nm). The intrinsic region width is set at 0.5, 0.7, and 1 μm. The inset reports the maximum responsivity for those conditions at 1.55 μm wavelength.

Fig. 4. Photodiode maximum theoretical −3  dB bandwidth.

Fig. 5. Schematic cross-sectional view of the final photodiode structure. Light coming from the waveguide is injected into the intrinsic region of the Ge photodiode perpendicularly to the schematics.

Fig. 6. Cross-sectional TEM image of the cavity after Ge epitaxy and CMP steps.

Fig. 7. Typical dark current characteristics of photodiodes A, B, and C (wi=0.5, 0.7, and 1 μm, respectively).

Fig. 8. Device capacitance as a function of reverse bias. A, B, and C type photodiodes have wi=0.5, 0.7, and 1 μm, respectively.

Fig. 9. (a) Photodiode frequency response at −3  V bias. For clarity purposes, the curves for photodiodes A and C were artificially shifted by +3 and −3  dB, respectively. (b) −3  dB opto-electrical bandwidth function of the applied reverse bias for the three photodiodes. A, B, and C type photodiodes have wi=0.5, 0.7, and 1 μm, respectively.

Fig. 10. TCAD simulated implantation profiles for the three designed intrinsic region widths, obtained by cross section along the dashed line shown in the inset of the figure.