Abstract

This paper experimentally demonstrates a design optimization of an evanescently-coupled waveguide germanium-on-silicon photodetector (PD) towards high-speed (> 30 Gb/s) applications. The resulting PD provides a responsivity of 1.09 A/W at 1550 nm, a dark current of 3.5 µA and bandwidth of 42.5 GHz at 2 V reverse-bias voltage. To optimize the PD, the impact of various design parameters on performance is investigated. A novel optimization methodology for the PD’s responsivity based on the required bandwidth is developed. The responsivity of the PD is enhanced by enlarging its geometry and using off-centered contacts on top of the germanium, while an integrated peaking inductor mitigates the inherent bandwidth reduction from the responsivity optimization. The performance of the optimized PD and the conventional, smaller size non-optimized PD is compared to validate the optimization methodology. The sensitivity of the optimized PD improves by 3.2 dB over a smaller size non-optimized PD. The paper further discusses the impact of top metal contacts on the photodetector’s performance.

© 2016 Optical Society of America

Full Article  |  PDF Article
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References

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    [Crossref]
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    [Crossref] [PubMed]
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    [Crossref]
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    [Crossref] [PubMed]
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    [Crossref] [PubMed]
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2016 (1)

2015 (2)

2014 (1)

2013 (1)

2012 (3)

2011 (2)

2010 (1)

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

2008 (1)

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

1997 (1)

J. R. Long and M. A. Copeland, “The modeling, characterization, and design of monolithic inductors for silicon RF IC’s,” IEEE J. Solid-State Circuits 32(3), 357–369 (1997).
[Crossref]

Absil, P.

Ang, K. W.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Armani, N.

Asghari, M.

Assanto, G.

Baehr-Jones, T.

Balakrishnan, S.

Bergman, K.

Capellini, G.

Chen, G.

Chen, H.

Chua, K. T.

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Colace, L.

Copeland, M. A.

J. R. Long and M. A. Copeland, “The modeling, characterization, and design of monolithic inductors for silicon RF IC’s,” IEEE J. Solid-State Circuits 32(3), 357–369 (1997).
[Crossref]

Cunningham, J. E.

De Coster, J.

De Heyn, P.

Deng, S.

Ding, R.

Dong, P.

Fang, Q.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

Feng, D.

Feng, N. N.

Ferrari, C.

Fong, J.

Gould, M.

Hochberg, M.

Knoll, D.

Krishnamoorthy, A. V.

Kroh, M.

Krune, E.

Kung, C. C.

Kwong, D. L.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Lazzarini, L.

Lepage, G.

Li, G.

Liang, H.

Liao, S.

Lim, A. E.

Liow, T. Y.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

Lischke, S.

Liu, L.

Liu, Y.

Lo, G. Q.

Y. Zhang, S. Yang, Y. Yang, M. Gould, N. Ophir, A. E. Lim, G. Q. Lo, P. Magill, K. Bergman, T. Baehr-Jones, and M. Hochberg, “A high-responsivity photodetector absent metal-germanium direct contact,” Opt. Express 22(9), 11367–11375 (2014).
[Crossref] [PubMed]

A. Novack, M. Gould, Y. Yang, Z. Xuan, M. Streshinsky, Y. Liu, G. Capellini, A. E. Lim, G. Q. Lo, T. Baehr-Jones, and M. Hochberg, “Germanium photodetector with 60 GHz bandwidth using inductive gain peaking,” Opt. Express 21(23), 28387–28393 (2013).
[Crossref] [PubMed]

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Long, J. R.

J. R. Long and M. A. Copeland, “The modeling, characterization, and design of monolithic inductors for silicon RF IC’s,” IEEE J. Solid-State Circuits 32(3), 357–369 (1997).
[Crossref]

Luo, Y.

Magill, P.

Mai, A.

Mai, C.

Masini, G.

Mekis, A.

Morii, K.

Nakano, Y.

Novack, A.

Ophir, N.

Peczek, A.

Qian, W.

Raj, K.

Roelkens, G.

Rossi, F.

Sahni, S.

Shafiiha, R.

Shen, L.

Shubin, I.

Song, J. F.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

Sorianello, V.

Streshinsky, M.

Sugiyama, M.

Takagi, S.

Takenaka, M.

Thacker, H.

Trusch, A.

Van Campenhout, J.

Verheyen, P.

Voigt, K.

Wang, J.

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Xiong, Y. Z.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

Xuan, Z.

Yang, S.

Yang, Y.

Yao, J.

Yao, W.

Yu, M. B.

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Yu, Y.

Zhang, X.

Zhang, Y.

Zheng, X.

Zhu, S. Y.

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

Zimmermann, L.

IEEE Electron Device Lett. (1)

K. W. Ang, S. Y. Zhu, J. Wang, K. T. Chua, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Novel silicon-carbon (Si: C) schottky barrier enhancement layer for dark-current suppression in Ge-on-SOI MSM photodetectors,” IEEE Electron Device Lett. 29(7), 704–707 (2008).
[Crossref]

IEEE J. Sel. Top. Quantum Electron. (1)

T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, and D. L. Kwong, “Silicon modulators and germanium photodetectors on SOI: monolithic integration, compatibility, and performance optimization,” IEEE J. Sel. Top. Quantum Electron. 16(1), 307–315 (2010).
[Crossref]

IEEE J. Solid-State Circuits (1)

J. R. Long and M. A. Copeland, “The modeling, characterization, and design of monolithic inductors for silicon RF IC’s,” IEEE J. Solid-State Circuits 32(3), 357–369 (1997).
[Crossref]

Opt. Express (9)

M. Takenaka, K. Morii, M. Sugiyama, Y. Nakano, and S. Takagi, “Dark current reduction of Ge photodetector by GeO2 surface passivation and gas-phase doping,” Opt. Express 20(8), 8718–8725 (2012).
[Crossref] [PubMed]

Y. Zhang, S. Yang, Y. Yang, M. Gould, N. Ophir, A. E. Lim, G. Q. Lo, P. Magill, K. Bergman, T. Baehr-Jones, and M. Hochberg, “A high-responsivity photodetector absent metal-germanium direct contact,” Opt. Express 22(9), 11367–11375 (2014).
[Crossref] [PubMed]

H. Chen, P. Verheyen, P. De Heyn, G. Lepage, J. De Coster, S. Balakrishnan, P. Absil, W. Yao, L. Shen, G. Roelkens, and J. Van Campenhout, “−1 V bias 67 GHz bandwidth Si-contacted germanium waveguide p-i-n photodetector for optical links at 56 Gbps and beyond,” Opt. Express 24(5), 4622–4631 (2016).
[Crossref]

S. Lischke, D. Knoll, C. Mai, L. Zimmermann, A. Peczek, M. Kroh, A. Trusch, E. Krune, K. Voigt, and A. Mai, “High bandwidth, high responsivity waveguide-coupled germanium p-i-n photodiode,” Opt. Express 23(21), 27213–27220 (2015).
[Crossref] [PubMed]

S. Liao, N. N. Feng, D. Feng, P. Dong, R. Shafiiha, C. C. Kung, H. Liang, W. Qian, Y. Liu, J. Fong, J. E. Cunningham, Y. Luo, and M. Asghari, “36 GHz submicron silicon waveguide germanium photodetector,” Opt. Express 19(11), 10967–10972 (2011).
[Crossref] [PubMed]

G. Li, Y. Luo, X. Zheng, G. Masini, A. Mekis, S. Sahni, H. Thacker, J. Yao, I. Shubin, K. Raj, J. E. Cunningham, and A. V. Krishnamoorthy, “Improving CMOS-compatible Germanium photodetectors,” Opt. Express 20(24), 26345–26350 (2012).
[Crossref] [PubMed]

M. Gould, T. Baehr-Jones, R. Ding, and M. Hochberg, “Bandwidth enhancement of waveguide-coupled photodetectors with inductive gain peaking,” Opt. Express 20(7), 7101–7111 (2012).
[Crossref] [PubMed]

A. Novack, M. Gould, Y. Yang, Z. Xuan, M. Streshinsky, Y. Liu, G. Capellini, A. E. Lim, G. Q. Lo, T. Baehr-Jones, and M. Hochberg, “Germanium photodetector with 60 GHz bandwidth using inductive gain peaking,” Opt. Express 21(23), 28387–28393 (2013).
[Crossref] [PubMed]

G. Chen, Y. Yu, S. Deng, L. Liu, and X. Zhang, “Bandwidth improvement for germanium photodetector using wire bonding technology,” Opt. Express 23(20), 25700–25706 (2015).
[Crossref] [PubMed]

Opt. Mater. Express (1)

Other (4)

T. Baehr-Jones, R. Ding, A. Ayazi, T. Pinguet, M. Streshinsky, N. Harris, J. Li, L. He, M. Gould, Y. Zhang, A. E. Lim, T. Y. Liow, S. H. Teo, G. Q. Lo, and M. Hochberg, “A 25 Gb/s silicon photonics platform,” arXiv preprint arXiv:1203.0767 (2012).

Lumerical Computation Solutions (TCAD software), https://www.lumerical.com/

L. Chrostowski and M. Hochberg, Silicon Photonics Design: from Devices to Systems (Cambridge U. 2015).

Y. Painchaud, M. Poulin, F. Pelletier, C. Latrasse, J. F. Gagné, S. Savard, G. Robidoux, M. Picard, S. Paquet, C. Davidson, M. Pelletier, M. Cyr, C. Paquet, M. Guy, M. Morsy-Osman, M. Chagnon, and D. V. Plant, “Silicon-based products and solutions,” SPIE OPTO, International Society for Optics and Photonics, 89880L–89880L (2014).

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Figures (15)

Fig. 1
Fig. 1 (a) Side-view and (b) top-view of a Ge-PD with a single electrode on top of the n-doped germanium (Ge-n ++ in dark green). (c) Side-view and (d) top view of a Ge-PD with two electrodes on top of the n-doped germanium.
Fig. 2
Fig. 2 The simulated electric field in a Ge-PD with a length of 25 µm, a width of 8 µm, and a thickness of 500 nm (linear scale). The Ge area is indicated by the white contour box. Left-side figures show the top view near the top interface of Ge (a) without top contact, (c) with one centered contact, (e) with two off-centered contacts. Right-side figures show the side view at the middle width of the Ge area for a PD (b) without top contact, (d) with one centered contact, (f) with two off-centered contacts.
Fig. 3
Fig. 3 Responsivity variation of the PD with various sizes of the Ge area. (a) For a PD with a constant length of 10 µm and various widths. (b) For a PD with a constant width of 8 µm and various lengths.
Fig. 4
Fig. 4 Dark current and bandwidth of the PD for various size of the Ge area. (a) The dark current of a PD with a constant length of 10 µm for various widths. (b) The dark current of a PD with a constant width of 8 µm for various lengths. (c) The bandwidth of a PD with a constant length of 10 µm for various widths, and (d) bandwidth of a PD with a constant width of 8 µm for various lengths.
Fig. 5
Fig. 5 Flowchart of the optimization methodology with target bandwidth BWT, calculated bandwidth BWL, and bandwidth peaking factor α
Fig. 6
Fig. 6 (a) Equivalent small-signal circuit of PD with peaking inductor. (b) The simulated frequency response of an 8 × 8 µm2 reference PD and a 20 × 8 µm2 PD with and without peaking inductor.
Fig. 7
Fig. 7 Simulated 50 Gb/s eye diagram of the 8 × 8 µm2 reference PD in comparison with the 20 × 8 µm2 PD (a) with the optimum peaking inductor (350 pH), and (b) with peaking inductor larger than the optimum value (540 pH).
Fig. 8
Fig. 8 (a) Fabricated photodetector with an integrated peaking spiral inductor. (b) Fabrication process layers.
Fig. 9
Fig. 9 (a) Measured S21 OE frequency response of the optimized PD (PD-D) at 2 V reverse-bias voltage and reference PD (PD-A) at 4 V reverse-bias voltage with their respective small-signal simulations, (b) Measured S22 (reflection) of both PDs with their respective small-signal simulations.
Fig. 10
Fig. 10 Test bed for the eye diagram and BER measurement.
Fig. 11
Fig. 11 (a) BER performance at 30 Gb/s for the reference PD (PD-A), the same size PD as the reference PD with two off-centered top contacts (PD-B), and 20 µm length PD with a centered top contact and peaking inductor (PD-C). (b) BER performance at 30 Gb/s for optimized PD (PD-D).
Fig. 12
Fig. 12 (top) Output electrical eye diagrams of the reference PD (PD-A) at various data rates. (bottom) output electrical eye diagram of optimized PD (PD-D) at corresponding data rates.
Fig. 13
Fig. 13 Measured and simulated responsivity (a), and measured and simulated dark current (b) for various PD lengths with one centered top contact and with two off-centered top contacts. Results are compared to simulation results from Figs. 3 and 4.
Fig. 14
Fig. 14 Normalized OE frequency response (S21) response of various PDs at 2 V.
Fig. 15
Fig. 15 Measured BER at 30 Gb/s of various devices at 4 V reverse-bias voltage.

Tables (3)

Tables Icon

Table 1 The parameters for the equivalent small-signal circuit of the reference PD and the longer PD with optimum peaking inductor and the longer PD with peaking inductor larger than optimum.

Tables Icon

Table 2 Summary of the photodetector’s dimensions and their measurements results.

Tables Icon

Table 3 Summary of device dimensions of fabricated PDs and their measurements results.

Metrics