Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product

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Significant progress has been made recently in demonstrating that silicon photonics is a promising technology for low-cost optical detectors, modulators and light sources1,2,3,4,5,6,7,8,9,10,11,12. It has often been assumed, however, that their performance is inferior to InP-based devices. Although this is true in most cases, one of the exceptions is the area of avalanche photodetectors, where silicon's material properties allow for high gain with less excess noise than InP-based avalanche photodetectors and a theoretical sensitivity improvement of 3 dB or more. Here, we report a monolithically grown germanium/silicon avalanche photodetector with a gain–bandwidth product of 340 GHz, a keff of 0.09 and a sensitivity of −28 dB m at 10 Gb s−1. This is the highest reported gain–bandwidth product for any avalanche photodetector operating at 1,300 nm and a sensitivity that is equivalent to mature, commercially available III–V compound avalanche photodetectors. This work paves the way for the future development of low-cost, CMOS-based germanium/silicon avalanche photodetectors operating at data rates of 40 Gb s−1 or higher.

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Figure 1: Summary of published gain–bandwidth products with respect to the multiplication layer thickness for InP-, InAlAs- and silicon-based APDs.
Figure 2: Schematic (a) and SEM (b) cross–sections of a germanium/silicon APD.
Figure 3: Direct current characteristics of a germanium/silicon APD.
Figure 4: Gain dependence of the excess noise and 3-dB bandwidth of the germanium/silicon APDs.
Figure 5: Back-to-back receiver sensitivity and eye diagram measurements for a 30-µm-diameter germanium/silicon APD receiver measured at 10 Gb s−1.


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This work was sponsored by Defense Advanced Research Projects Agency (DARPA) under contract number HR0011-06-3-0009 and is supervised by J. Shah in the Microsystems Technology Office (MTO) office. The authors thank T. Liu, S. Yeh and C. Xie for assistance in device sensitivity measurements.

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Correspondence to Yimin Kang.

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Kang, Y., Liu, H., Morse, M. et al. Monolithic germanium/silicon avalanche photodiodes with 340 GHz gain–bandwidth product. Nature Photon 3, 59–63 (2009) doi:10.1038/nphoton.2008.247

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