High-speed short-wavelength silicon photodetectors fabricated in 130-nm CMOS process

We have integrated several optoelectronic devices into deep-submicron silicon fabrication process. The main results for monolithic integration of silicon planar interdigitated P-I-N photodiodes with transimpedance amplifiers and waveguide grating couplers will be reviewed. The integration process was carried out in an unmodified 130nm CMOS process flow, on SOI substrates. Photodetectors that were fabricated on 200nm-thick SOI exhibited a 3dB electrical bandwidth of 10GHz for -5V bias while the photodetectors fabricated on 2000nm-thick SOI had 8GHz 3dB electrical bandwidth for -28V bias. The external quantum efficiency of the 2000nm-thick photodetectors at 835nm was 14%. The 200nm-thick photodetectors were integrated with waveguide grating couplers. For 835nm, the external quantum efficiency of the photodetector improved from 3% to 12% when a diffraction grating with 265nm period was integrated on top of the photodiode. The 3dB electrical bandwidth of these photodetectors was 4.1GHz (RC limited). The dark current for these devices was 10pA at -3V bias for an area of 2500mm2. The photodetectors fabricated on 2000nm-thick SOI substrates were wire-bonded to SiGe transimpedance amplifiers with 184W transimpedance gain. When the photodiode was used in avalanche operation mode the sensitivity of -7dBm (BER<10-9) was achieved at 10Gb/s. The multiplication gain for the avalanche photodetector was in this case M=4. This is the highest speed reported for an all-silicon optical receiver.