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Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 22, Iss. 6 — Mar. 24, 2014
  • pp: 7261–7268
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Fringe-field carrier-depletion modulators with high modulation efficiency and low free carrier absorption

Kai-Ning Ku and Ming-Chang M. Lee  »View Author Affiliations


Optics Express, Vol. 22, Issue 6, pp. 7261-7268 (2014)
http://dx.doi.org/10.1364/OE.22.007261


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Abstract

A high-speed carrier-depletion silicon modulator based on a fringe field pn junction design is presented. Due to the strong fringe field, the size of heavily doped regions can be reduced and away from the waveguide core, whereas large modulation efficiency is still accomplishable. The VπL is 1.8 V-cm and the phase shifter loss is 1.3 dB/mm. The figure of merit (FOM), defined by the product of VπL and phase shifter loss, is estimated to be 23.4 dB-V. The modulation speed and depth are 11.8 GHz and 8.1 dB, respectively, which is mainly limited by the mobility of poly-Si.

© 2014 Optical Society of America

1. Introduction

In general, free-carrier dispersion modulators can be categorized into three types -carrier accumulation [10

10. A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, and M. Paniccia, “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature 427(6975), 615–618 (2004). [CrossRef] [PubMed]

], injection [11

11. W. M. Green, M. J. Rooks, L. Sekaric, and Y. A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Opt. Express 15(25), 17106–17113 (2007). [CrossRef] [PubMed]

] and depletion [9

9. D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, and G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express 19(12), 11507–11516 (2011). [CrossRef] [PubMed]

], according to the mechanism of manipulating free carriers. Usually, devices operated by carrier depletion have advantage in high modulation speed because of short majority carrier lifetime [9

9. D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, and G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express 19(12), 11507–11516 (2011). [CrossRef] [PubMed]

, 15

15. A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N. Izhaky, and M. Paniccia, “High-speed optical modulation based on carrier depletion in a silicon waveguide,” Opt. Express 15(2), 660–668 (2007). [CrossRef] [PubMed]

]. However, the modulation efficiency in terms of the length of π phase shift multiplied by the operating voltage (VπL) is often not as superior as the injection type modulators, resulting in a large device footprint. To overcome this issue, engineering the doping profile of pn junctions near the waveguide to achieve maximum overlap integral between the optical mode and the modulated depletion region has been widely investigated [21

21. G. T. Reed, G. Z. Mashanovich, F. Y. Gardes, M. Nedeljkovic, Y. Hu, D. J. Thomson, K. Li, P. R. Wilson, S. W. Chen, and S. S. Hsu, “Recent breakthroughs in carrier depletion based silicon optical modulators,” Nanophotonics 0(0), 1–18 (2013). [CrossRef]

]. Generally, the heavily doped region should be as close to the waveguide center as possible for reducing the driving voltage and achieving a wide dynamic range of depletion modulation. However, the free carrier absorption increases accordingly because of this heavily doped region. So far, there have been a variety of device designs for reducing phase shifter loss presented in recent years, such as pipin diodes [14

14. M. Ziebell, D. Marris-Morini, G. Rasigade, J. M. Fédéli, P. Crozat, E. Cassan, D. Bouville, and L. Vivien, “40 Gbit/s low-loss silicon optical modulator based on a pipin diode,” Opt. Express 20(10), 10591–10596 (2012). [CrossRef] [PubMed]

] and a doping compensation method [8

8. X. Tu, T. Y. Liow, J. Song, M. Yu, and G. Q. Lo, “Fabrication of low loss and high speed silicon optical modulator using doping compensation method,” Opt. Express 19(19), 18029–18035 (2011). [CrossRef] [PubMed]

]. Nevertheless, each of them needs to stringently control the doping profile to keep the modulation efficient while avoid strong free carrier absorption as well. In this study, we propose a new device structure to employ fringe-field pn junctions by deploying heavily doped regions just near the corners of the waveguide to alleviate free carrier absorption. Meanwhile, the large fringe field at these doped regions effectively depletes the carriers to achieve extended depletion region across the waveguide center and the measured VπL is 1.8 V-cm. These doped regions can be precisely controlled by self-aligned ion implantation as well as a post annealing process.

2. Device operation principle and fabrication

The device structure is illustrated in Fig. 1.
Fig. 1 Fringe-field carrier depletion modulators: device structure and doping profile.
Fig. 2 Optical and electrical simulations: (a) optical mode profile inside the waveguide. (b) depletion region at zero bias (the shadow region), and (c) depletion region (the shadow region) at −6V reverse bias. (d-e) electric fields at zero and −6V reverse bias, respectively.
Two symmetric n + doped regions are deployed at the bottom corners of a p-doped Si rib waveguide, and a thin p + poly Si layer caps the top to form two parallel fringe field pn junctions. The optical mode field is shown in Fig. 2(a), which is simulated by FIMMWAVE (Photon Design, Ltd.). Figures 2(b)-2(e) show the simulated depletion regions and electric fields by Medici (Synopsys, Ltd.). At 0V bias, the depletion regions are just localized at the corners, away from the waveguide core as depicted in Fig. 2(b); nevertheless, as the reversed bias increases to −6 V, the two depletion regions extend and eventually merge to deplete all the free carriers at the waveguide center as seen in Fig. 2(c). Through this design, the modulated depletion region has a large overlap integral with the optical guided mode while the highly doped region doesn’t. Meanwhile, the fringe field is strong (seen in Figs. 2(d)-2(e)), which makes the device modulated more efficiently with a small operating voltage.

To get an insight into the fringe field modulation scheme, we compare two conventional depletion-type modulators; one is based on a lateral pn junction and the other is a vertical pn junction. For equally comparing these three structures, all these devices have the same waveguide dimensions, including the rib height, rib width and slab thickness, as well as the dopant concentration for the n- and p-type Si. The structure and dopant concentration are listed in Fig. 3.
Fig. 3 Comparison among different configurations of pn junctions for free-carrier dispersion modulation. The green arrows denote the direction of varied depletion region from 0 V to −6 V.
The n + doped regions are positioned inside the waveguide and intentionally offset by 80 nm from the waveguide center for the vertical (model 1) and lateral (model 2) pn junctions such that the depletion region can extend to the waveguide center, under a given operating voltage of −6 V. On the other hand, the n + doping regions of the fringe-field pn junction are distributed near the corners of the rib to modulate the depletion region across the waveguide. The figure of merit (FOM) of phase modulation, defined by the product of VπL and the attenuation coefficient α, is observed to be the lowest (best) for the fringe field pn junction according to the simulation result. It can be suggested by the fact that the n + doped regions are deployed to be farthest from the waveguide center for reducing the free carrier absorption, while the large modulation depth is still attainable due to the strong fringe field of the parallel pn junctions at the corners.

The fringe-field carrier-depletion modulator is implemented on a silicon-on-insulator (SOI) wafer with 340 nm device Si and 2 μm buried oxide (BOX). The fabrication process is illustrated in Fig. 4.
Fig. 4 Device process flow (not including the backend process for metal contact).
Fig. 5 Simulated phosphorus profiles (a) before and (b) after post-annealing. The simulation is done by the software TSUPREM-4
First, an ion implantation is used to define the p-type active region of the modulator. A SiO2 film is then deposited and patterned as the hard mask for waveguide etching. Next, another SiO2 film of 50 nm is coated around the waveguide and etched back to create a 50-nm thick sidewall spacer. The n + Si is thus defined by self-aligned ion implantation of phosphorus, followed by a post annealing process to drive phosphorus atoms into the waveguide. Phosphorus ion diffusion in Si is a common process in electron device fabrication; therefore, the doped region and profile are able to be precisely engineered. The simulated phosphorus profiles before and after post annealing are displayed in Fig. 5, where the contours outline the dopant concentration corresponding to the process step in Fig. 4(j).It is feasible to make the depletion regions bilaterally extend to the waveguide core with a control voltage close to the design value (−6V in this case). In fact, this procedure is similar to a standard process for defining the source and drain of metal–oxide–semiconductor field-effect transistors (MOSFETs). To better confine the guided mode in the lightly doped waveguide rib, the waveguide slab is further thinned down to 50 nm through a dry etching process, as depicted in Fig. 4(h). The optical mode is thus squeezed within the rib to achieve a maximal mode overlap with the modulated depletion region while minimize optical loss caused by free carrier absorption in the heavily doped regions. After removal of the SiO2 hard mask, a thick oxide film is deposited and planarized by chemical mechanical polishing (CMP) till the surface topography is flat. This oxide layer is further etched back to expose the waveguide rib capped with a p + poly-Si of 100 nm thick, as illustrated in Figs. 4(l)-4(m). The fabricated device is shown in Fig. 6.
Fig. 6 Scanning electron microscope image of the fabricated device (cross section).
The yellow dash lines mark the pn junctions.

3. Measurement and characterization

The fringe-field carrier-depletion modulator is characterized by measuring the transmission spectra of an asymmetric waveguide-based Mach–Zehnder interferometer (MZI) constructed by this modulator, where the length of phase shift is 750 μm and the path difference between the two arms is 205 μm. The extinction ratio of the MZI exceeds 20 dB for transverse electric (TE) waves, and the spectrum varies with the bias voltage. The transmission spectrum and phase shift versus the bias voltage are shown in Fig. 7(a) and 7(b), respectively.
Fig. 7 (a) Transmission spectra of the asymmetric MZI modulator. (b) Phase shift versus bias voltages.
By excluding the fiber-waveguide coupling loss and the 3-dB coupler loss, the phase shifter loss is characterized to be 1.3 dB/mm (without bias). The modulation efficiency (VπL) is 1.8 V-cm at −6 V with a feature of good linearity. The FOM of the device is 23.4 V-dB. The modulation depth is estimated to be 8.1 dB at 1556.3 nm wavelength, as illustrated in Fig. 8.
Fig. 8 Extinction ratios of the asymmetric MZI modulator versus different bias voltages at 1556.3 nm.

To examine the operation speed, the device RC time constant is characterized by measuring the I-V and C-V characteristics. The result is shown in Fig. 9.
Fig. 9 Electrical properties of devices: (a) I-V and (b) C-V characteristics.
The series resistance (R) is 12.5 Ω and the capacitance (C) is 1 pF. The corresponding cutoff frequency is estimated to be 12.7 GHz via the formula fc = 1/(2πRC). The series resistance is a little bit higher than expectation, which could be due to low mobility of poly-Si capped on the rib waveguide. To verify the resistance mainly contributed by poly-Si, the transmission line method (TLM) is used to find the contact resistance and the resistivity of poly-Si [22

22. G. K. Reeves and H. B. Harrison, “Obtaining the Specific contact resistance from transmission-line model measurements,” IEEE Electron Device Lett. 3(5), 111–113 (1982). [CrossRef]

], which is measured to be 0.32 Ω-cm. By referring to the experimental data reported in [23

23. T. Kamins, Polycrystalline Silicon for Integrated Circuits and Displays (Kluwer Academic Publishers, 1998).

], the carrier mobility of poly-Si is 10 times lower than that of c-Si under a doping concentration of 5 x 1017 cm−3. The resistance of capped poly-Si is thus estimated to be 8.5 Ω.

The device dynamic response is characterized by applying a 10 GHz square wave signal with Vpp = 6 V and Vdc = −3.5 V on the modulator via a Ground-Signal-Ground (G-S-G) RF probe. The launched wavelength is 1556.3 nm and the received optical signal is collected by a digital communications analyzer (Agilent 86100C). The signal trace is shown in Fig. 10(a).
Fig. 10 High-frequency measurement: (a) the dynamic response of device transmittance and (b) the eye diagram.
The rise/fall time is measured to be 29.56 ps, indicating that the 3-dB operation bandwidth is 11.8 GHz according to the formula BW = 0.35/tr, where tr is either the fall time or rise time. The VπL is a little bit higher than the simulated value and the operation speed is lower than the state-of-the-art c-Si depletion mode modulators. This is because the top p + cap layer is made of poly-Si. If the cap layer is replaced with c-Si grown by selective epitaxy [24

24. P. Sangwoo, S. Taichi, J. P. Denton, and G. W. Neudeck, “Multiple layers of silicon- on-insulator islands fabrication by selective epitaxial growth,” IEEE Electron Device Lett. 20(5), 194–196 (1999). [CrossRef]

], the FOM can be lower than 20 dB-V and the operation speed can be beyond 30 GHz. Figure 10(b) shows a 10 GHz eye diagram of received optical signals generated from a pseudo random binary sequence (PRBS) source.

4. Conclusion

A new Si modulator implemented by fringe-field carrier depletion is demonstrated. Through the strong fringe field, the depletion regions of two parallel pn junctions near the waveguide corners are efficiently modulated across the waveguide center without introducing too much free carrier absorption.

Table 1. Summary list of Si MZI modulators with different device configurations

table-icon
View This Table
Table 1 lists the key indices of reported Si modulators. The measured VπL and attenuation coefficient of the fringe-field carrier depletion modulator are 1.8 V-cm and 1.3 dB/mm, respectively. The FOM is 23.4 V-dB. The modulation bandwidth is 11.8 GHz, mainly limited by the mobility of capped poly-Si. The operation speed can be potentially beyond 30 GHz by replacing poly-Si with c-Si. The fringe-field pn junctions can be precisely defined through a self-aligned ion implantation and a subsequent thermal drive-in process without critical process control.

Acknowledgments

The authors acknowledge the funding support from National Science Council (NSC100-2628-E-007-027-MY3) in Taiwan and the assistance of high-frequency measurement by Prof. Kai-Ming Feng from Dept. of Electrical Engineering, National Tsing Hua University, Taiwan.

References and links

1.

C. Dragone, “An N*N optical multiplexer using a planar arrangement of two star couplers,” IEEE Photon. Technol. Lett. 3(9), 812–815 (1991). [CrossRef]

2.

C. Dragone, C. A. Edwards, and R. C. Kistler, “Integrated optics N*N multiplexer on silicon,” IEEE Photon. Technol. Lett. 3(10), 896–899 (1991). [CrossRef]

3.

X. Fang and R. O. Claus, “Polarization-independent all-fiber wavelength-division multiplexer based on a Sagnac interferometer,” Opt. Lett. 20(20), 2146–2148 (1995). [CrossRef] [PubMed]

4.

D. W. Kim, A. Barkai, R. Jones, N. Elek, H. Nguyen, and A. Liu, “Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers,” Opt. Lett. 33(5), 530–532 (2008). [CrossRef] [PubMed]

5.

H. Takahashi, K. Oda, and H. Toba, “Impact of crosstalk in an arrayed-waveguide multiplexer on NxN optical interconnection,” J. Lightwave Technol. 14(6), 1097–1105 (1996). [CrossRef]

6.

H. Talahashi, K. Oda, H. Toba, and Y. Inoue, “Transmission characteristics of arrayed waveguide N×N wavelength multiplexer,” J. Lightwave Technol. 13(3), 447–455 (1995). [CrossRef]

7.

W. C. Chiu, C. Y. Lu, and M. C. M. Lee, “Monolithic integration of 2-D multimode interference couplers and silicon photonic wires,” IEEE J. Sel. Top. Quantum Electron. 17(3), 540–545 (2011). [CrossRef]

8.

X. Tu, T. Y. Liow, J. Song, M. Yu, and G. Q. Lo, “Fabrication of low loss and high speed silicon optical modulator using doping compensation method,” Opt. Express 19(19), 18029–18035 (2011). [CrossRef] [PubMed]

9.

D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, and G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express 19(12), 11507–11516 (2011). [CrossRef] [PubMed]

10.

A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, and M. Paniccia, “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature 427(6975), 615–618 (2004). [CrossRef] [PubMed]

11.

W. M. Green, M. J. Rooks, L. Sekaric, and Y. A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Opt. Express 15(25), 17106–17113 (2007). [CrossRef] [PubMed]

12.

Q. Xu, S. Manipatruni, B. Schmidt, J. Shakya, and M. Lipson, “12.5 Gbit/s carrier-injection-based silicon micro-ring silicon modulators,” Opt. Express 15(2), 430–436 (2007). [CrossRef] [PubMed]

13.

Q. Xu, B. Schmidt, S. Pradhan, and M. Lipson, “Micrometre-scale silicon electro-optic modulator,” Nature 435(7040), 325–327 (2005). [CrossRef] [PubMed]

14.

M. Ziebell, D. Marris-Morini, G. Rasigade, J. M. Fédéli, P. Crozat, E. Cassan, D. Bouville, and L. Vivien, “40 Gbit/s low-loss silicon optical modulator based on a pipin diode,” Opt. Express 20(10), 10591–10596 (2012). [CrossRef] [PubMed]

15.

A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N. Izhaky, and M. Paniccia, “High-speed optical modulation based on carrier depletion in a silicon waveguide,” Opt. Express 15(2), 660–668 (2007). [CrossRef] [PubMed]

16.

D. Ahn, C. Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, and F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007). [CrossRef] [PubMed]

17.

C. K. Tseng, W. T. Chen, K. H. Chen, H. D. Liu, Y. Kang, N. Na, and M. C. M. Lee, “A self-assembled microbonded Germanium/Silicon heterojunction photodiodes for 25 Gb/s high-speed optical interconnects,” Scientific Report 3 (2013).

18.

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]

19.

L. Vivien, J. Osmond, J. M. Fédéli, D. Marris-Morini, P. Crozat, J. F. Damlencourt, E. Cassan, Y. Lecunff, and S. Laval, “42 GHz p.i.n Germanium photodetector integrated in a silicon-on-insulator waveguide,” Opt. Express 17(8), 6252–6257 (2009). [CrossRef] [PubMed]

20.

T. T. Wu, C. Y. Chou, M. C. Lee, and N. Na, “A critically coupled Germanium photodetector under vertical illumination,” Opt. Express 20(28), 29338–29346 (2012). [CrossRef] [PubMed]

21.

G. T. Reed, G. Z. Mashanovich, F. Y. Gardes, M. Nedeljkovic, Y. Hu, D. J. Thomson, K. Li, P. R. Wilson, S. W. Chen, and S. S. Hsu, “Recent breakthroughs in carrier depletion based silicon optical modulators,” Nanophotonics 0(0), 1–18 (2013). [CrossRef]

22.

G. K. Reeves and H. B. Harrison, “Obtaining the Specific contact resistance from transmission-line model measurements,” IEEE Electron Device Lett. 3(5), 111–113 (1982). [CrossRef]

23.

T. Kamins, Polycrystalline Silicon for Integrated Circuits and Displays (Kluwer Academic Publishers, 1998).

24.

P. Sangwoo, S. Taichi, J. P. Denton, and G. W. Neudeck, “Multiple layers of silicon- on-insulator islands fabrication by selective epitaxial growth,” IEEE Electron Device Lett. 20(5), 194–196 (1999). [CrossRef]

OCIS Codes
(250.0250) Optoelectronics : Optoelectronics
(250.4110) Optoelectronics : Modulators

ToC Category:
Optoelectronics

History
Original Manuscript: February 19, 2014
Revised Manuscript: March 13, 2014
Manuscript Accepted: March 14, 2014
Published: March 20, 2014

Citation
Kai-Ning Ku and Ming-Chang M. Lee, "Fringe-field carrier-depletion modulators with high modulation efficiency and low free carrier absorption," Opt. Express 22, 7261-7268 (2014)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-22-6-7261


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References

  1. C. Dragone, “An N*N optical multiplexer using a planar arrangement of two star couplers,” IEEE Photon. Technol. Lett. 3(9), 812–815 (1991). [CrossRef]
  2. C. Dragone, C. A. Edwards, R. C. Kistler, “Integrated optics N*N multiplexer on silicon,” IEEE Photon. Technol. Lett. 3(10), 896–899 (1991). [CrossRef]
  3. X. Fang, R. O. Claus, “Polarization-independent all-fiber wavelength-division multiplexer based on a Sagnac interferometer,” Opt. Lett. 20(20), 2146–2148 (1995). [CrossRef] [PubMed]
  4. D. W. Kim, A. Barkai, R. Jones, N. Elek, H. Nguyen, A. Liu, “Silicon-on-insulator eight-channel optical multiplexer based on a cascade of asymmetric Mach-Zehnder interferometers,” Opt. Lett. 33(5), 530–532 (2008). [CrossRef] [PubMed]
  5. H. Takahashi, K. Oda, H. Toba, “Impact of crosstalk in an arrayed-waveguide multiplexer on NxN optical interconnection,” J. Lightwave Technol. 14(6), 1097–1105 (1996). [CrossRef]
  6. H. Talahashi, K. Oda, H. Toba, Y. Inoue, “Transmission characteristics of arrayed waveguide N×N wavelength multiplexer,” J. Lightwave Technol. 13(3), 447–455 (1995). [CrossRef]
  7. W. C. Chiu, C. Y. Lu, M. C. M. Lee, “Monolithic integration of 2-D multimode interference couplers and silicon photonic wires,” IEEE J. Sel. Top. Quantum Electron. 17(3), 540–545 (2011). [CrossRef]
  8. X. Tu, T. Y. Liow, J. Song, M. Yu, G. Q. Lo, “Fabrication of low loss and high speed silicon optical modulator using doping compensation method,” Opt. Express 19(19), 18029–18035 (2011). [CrossRef] [PubMed]
  9. D. J. Thomson, F. Y. Gardes, Y. Hu, G. Mashanovich, M. Fournier, P. Grosse, J.-M. Fedeli, G. T. Reed, “High contrast 40Gbit/s optical modulation in silicon,” Opt. Express 19(12), 11507–11516 (2011). [CrossRef] [PubMed]
  10. A. Liu, R. Jones, L. Liao, D. Samara-Rubio, D. Rubin, O. Cohen, R. Nicolaescu, M. Paniccia, “A high-speed silicon optical modulator based on a metal-oxide-semiconductor capacitor,” Nature 427(6975), 615–618 (2004). [CrossRef] [PubMed]
  11. W. M. Green, M. J. Rooks, L. Sekaric, Y. A. Vlasov, “Ultra-compact, low RF power, 10 Gb/s silicon Mach-Zehnder modulator,” Opt. Express 15(25), 17106–17113 (2007). [CrossRef] [PubMed]
  12. Q. Xu, S. Manipatruni, B. Schmidt, J. Shakya, M. Lipson, “12.5 Gbit/s carrier-injection-based silicon micro-ring silicon modulators,” Opt. Express 15(2), 430–436 (2007). [CrossRef] [PubMed]
  13. Q. Xu, B. Schmidt, S. Pradhan, M. Lipson, “Micrometre-scale silicon electro-optic modulator,” Nature 435(7040), 325–327 (2005). [CrossRef] [PubMed]
  14. M. Ziebell, D. Marris-Morini, G. Rasigade, J. M. Fédéli, P. Crozat, E. Cassan, D. Bouville, L. Vivien, “40 Gbit/s low-loss silicon optical modulator based on a pipin diode,” Opt. Express 20(10), 10591–10596 (2012). [CrossRef] [PubMed]
  15. A. Liu, L. Liao, D. Rubin, H. Nguyen, B. Ciftcioglu, Y. Chetrit, N. Izhaky, M. Paniccia, “High-speed optical modulation based on carrier depletion in a silicon waveguide,” Opt. Express 15(2), 660–668 (2007). [CrossRef] [PubMed]
  16. D. Ahn, C. Y. Hong, J. Liu, W. Giziewicz, M. Beals, L. C. Kimerling, J. Michel, J. Chen, F. X. Kärtner, “High performance, waveguide integrated Ge photodetectors,” Opt. Express 15(7), 3916–3921 (2007). [CrossRef] [PubMed]
  17. C. K. Tseng, W. T. Chen, K. H. Chen, H. D. Liu, Y. Kang, N. Na, and M. C. M. Lee, “A self-assembled microbonded Germanium/Silicon heterojunction photodiodes for 25 Gb/s high-speed optical interconnects,” Scientific Report 3 (2013).
  18. T. Y. Liow, K. W. Ang, Q. Fang, J. F. Song, Y. Z. Xiong, M. B. Yu, G. Q. Lo, 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]
  19. L. Vivien, J. Osmond, J. M. Fédéli, D. Marris-Morini, P. Crozat, J. F. Damlencourt, E. Cassan, Y. Lecunff, S. Laval, “42 GHz p.i.n Germanium photodetector integrated in a silicon-on-insulator waveguide,” Opt. Express 17(8), 6252–6257 (2009). [CrossRef] [PubMed]
  20. T. T. Wu, C. Y. Chou, M. C. Lee, N. Na, “A critically coupled Germanium photodetector under vertical illumination,” Opt. Express 20(28), 29338–29346 (2012). [CrossRef] [PubMed]
  21. G. T. Reed, G. Z. Mashanovich, F. Y. Gardes, M. Nedeljkovic, Y. Hu, D. J. Thomson, K. Li, P. R. Wilson, S. W. Chen, S. S. Hsu, “Recent breakthroughs in carrier depletion based silicon optical modulators,” Nanophotonics 0(0), 1–18 (2013). [CrossRef]
  22. G. K. Reeves, H. B. Harrison, “Obtaining the Specific contact resistance from transmission-line model measurements,” IEEE Electron Device Lett. 3(5), 111–113 (1982). [CrossRef]
  23. T. Kamins, Polycrystalline Silicon for Integrated Circuits and Displays (Kluwer Academic Publishers, 1998).
  24. P. Sangwoo, S. Taichi, J. P. Denton, G. W. Neudeck, “Multiple layers of silicon- on-insulator islands fabrication by selective epitaxial growth,” IEEE Electron Device Lett. 20(5), 194–196 (1999). [CrossRef]

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