OSA's Digital Library

Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 20, Iss. 2 — Jan. 16, 2012
  • pp: 1096–1101
« Show journal navigation

Zero-bias 40Gbit/s germanium waveguide photodetector on silicon

Laurent Vivien, Andreas Polzer, Delphine Marris-Morini, Johann Osmond, Jean Michel Hartmann, Paul Crozat, Eric Cassan, Christophe Kopp, Horst Zimmermann, and Jean Marc Fédéli  »View Author Affiliations


Optics Express, Vol. 20, Issue 2, pp. 1096-1101 (2012)
http://dx.doi.org/10.1364/OE.20.001096


View Full Text Article

Acrobat PDF (1012 KB)





Browse Journals / Lookup Meetings

Browse by Journal and Year


   


Lookup Conference Papers

Close Browse Journals / Lookup Meetings

Article Tools

Share
Citations

Abstract

We report on lateral pin germanium photodetectors selectively grown at the end of silicon waveguides. A very high optical bandwidth, estimated up to 120GHz, was evidenced in 10 µm long Ge photodetectors using three kinds of experimental set-ups. In addition, a responsivity of 0.8 A/W at 1550 nm was measured. An open eye diagrams at 40Gb/s were demonstrated under zero-bias at a wavelength of 1.55 µm.

© 2012 OSA

1. Introduction

2. Fabrication

Several issues have to be circumvented in order to fabricate high performance, near infra-red Ge PDs integrated at the end of silicon waveguide: (i) the several hundreds of nanometer deep recess at the end of optical waveguides have to be selectively filled with Ge, (ii) the Ge thickness has to be well controlled to have a good coupling between the Si waveguide and the Ge detector and (iii) the quality of the germanium layer grown on silicon has to be optimum to reduce dark current.

2.1 Selective Epitaxial Growth of Ge in recess at the end of optical waveguides

We thus typically proceed as follows. A dedicated surface preparation is first of all used to get rid of native oxide and contaminants on the cavities’ floors and Si sidewalls. GeH4 is then flown at 400°C at 100 Torr pressure in our 200 mm Applied Materials Epi Centura Reduced Pressure Chemical Vapour Deposition (RP-CVD) tool in order to accommodate, in a several tens of nm thick flat Ge layer, the lattice mismatch between Ge and Si. Although the growth front is as expected a bit rough [16

16. J. M. Hartmann, A. Abbadie, N. Cherkashin, H. Grampeix, and L. Clavelier, “Epitaxial growth of Ge thick layers on nominal and 6° off Si(001); Ge surface passivation by Si,” Semicond. Sci. Technol. 24, 055002–055005 (2009).

], faceting is not present at that stage even when the growth time is 5 times larger than the time typically used (i.e. 300s instead of 60s). This is clearly illustrated by the top two 3D Atomic Force Microscopy (AFM) images of Fig. 1a and the bottom two sections of Fig. 1b. Temperature is then slowly ramped-up (2.5°C/s) to 750°C, at which the remainder of the Ge layer is grown in a few minutes (at 20 Torr). {111}, {113} and higher Miller index faceting is then present at the cavity edges, as illustrated by the bottom 3D AFM images of Fig. 1a and the top three sections of Fig. 1b. Ge overflow from the recess (i.e. more than 1 µm layers, typically; rightmost two images of Fig. 1a) is aimed for, in order to suppress coupling issues and reduce the defect density, which has been shown to exponentially decrease with the deposited thickness [18

18. G. Wang, R. Loo, E. Simoen, L. Souriau, M. Caymax, M. M. Heyns, and B. Blanpain, “A model of threading dislocation density in strain-relaxed Ge and GaAs epitaxial films on Si (100),” Appl. Phys. Lett. 94(10), 102115 (2009). [CrossRef]

,19

19. Y. Yamamoto, P. Zaumseil, T. Arguirov, M. Kittler, and B. Tillack, “Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD,” Solid-State Electron. 60(1), 2–6 (2011). [CrossRef]

]. Thermal annealing at 750°C for 1 hour or very short thermal cycling between 750°C and 890°C is then performed under H2 just after growth in order to further reduce the defect density without deleterious GeSi alloying. Finally, Chemical Mechanical Polishing (CMP) is used in order to (i) get rid of the excess Ge at cavity locations and (ii) remove the poly-Ge nuclei present on the surrounding SiO2. The imperfect selectivity is likely due to the use here of an initially 800 nm thick SiO2 layer deposited at 520°C then polished down to 700 nm, whose resulting surface is apparently of lesser quality than thermally grown SiO2. Furthermore, a specific growth rate calibration is mandatory each time the lithography mask layout is changed due to strong loading effects. Indeed, for the F(GeH4)/F(H2) mass-flow ratio (2.5x10−4) used in this work, Ge growth rates were for 10 µm x 10 µm windows 16-17 times those on blanket wafers, with ~45 and 260 nm min.−1 growth rates at 400°C and 750°C, respectively. Loading effects in similar dimension cavities but other chip designs were found to be in the 10 - 60 range.

2.2 Fabrication of the waveguide Ge detector

The process used in this work is compatible with CMOS technology. First, the silicon waveguides were fabricated using 193nm Deep-UV lithography followed by HBr dry etching. Its geometry was the following: the height was 220nm, the width was 500nm. A 10µm long silicon recess was etched at the end of the waveguide down to a thin silicon layer of about 50nm. Ge was selectively grown by RP-CVD in the Si cavity using the process described in sub-section 2.1. After CMP, a silica layer was deposited and a self-aligning process was used to perfectly define n-type and p-type doped regions, that were implanted with phosphorous and boron ions, respectively. Rapid thermal annealing was subsequently used to activate the dopants. A 1µm thick SiO2 was deposited and planarized before etching 400nm diameter vias in it. These vias were filled with TiNW and planarized in order to get W plugs. A Ti/TiN/AlCu metal stack was deposited on this flat surface and lithography together and Cl2 etching were used to fabricate metallic contacts. A schematic view of the lateral photodiode is presented in Fig. 2a
Fig. 2 (a) Schematic view of a lateral pin Ge photodetector integrated at the end of a Si waveguide. The length was 10 µm. (b) Top-view Optical Microscopy and cross-sectional SEM images of the Ge PD. (c) SEM cross-section (perpendicular to the waveguide direction).
. Top view optical microscopy and cross-sectional Scanning Electron Microscopy (SEM) images of the Ge photodetector at the end of the Si waveguide are shown in Figs. 2b and 2c. The doped region spacing (i-Ge width) design was 500nm.

3. Results

The optical responsivity of the Ge photodetector was measured at a wavelength of 1.55µm using a reference waveguide to estimate the injected power as described in Ref. [6

6. 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]

]. A responsivity of 0.8 A/W at a wavelength of 1550nm was measured, as shown in Fig. 3
Fig. 3 Responsivity versus reverse bias voltage for the 10µm long lateral pin Ge photodetector integrated at the end of a Si waveguide.
. Saturation value was already obtained at 0.1V, showing a good collection efficiency of photo-generated carriers. At zero-bias, the responsivity is still as high as 0.78 A/W. This high value, close to published record, demonstrates the good coupling efficiency between the Si waveguide and the lateral Ge photodetector and the efficiency of complete light absorption after a 10µm propagation length thanks to the butt coupling configuration used here.

The cut-off frequency at 1.55µm of the integrated photodetectors was determined using three different opto-RF experiments (Fig. 4
Fig. 4 Normalized optical responses as a function of frequency under −2V bias at the wavelength of 1.55µm. The photodetector length was 10 µm.
). The first measurement was based on the use of a 50GHz modulator calibrated with a 65GHz detector, which gave a cut-off frequency at −3dB much higher than 50GHz. Given those results, a 67GHz Lightwave component analyzer from Agilent (N4373C) was used. A bandwidth higher than 67GHz is still obtained leading difficult to estimate the bandwidth. The third experiment to determine the bandwidth was then based on the beating of two near optical lasers coupled with a 110GHz electrical spectrum analyzer. These measurements shown that the bandwidth is much higher than 50Ghz and it can be roughly estimated of about 120GHz. According to the transit time calculation, the maximum bandwidth should be about 53Ghz using the design i-Ge width of 500nm. However, after thermal annealing for dopant activation, dopant drift occurred and reduced the i-Ge width which explains the very high measured bandwidth.

The viability of the performances of this Ge waveguide PD was checked by measuring the data transmission at 40Gb/s. To perform these measurements the RF signal from a pseudo-random bit sequence (PRBS) generator was used to drive a LiNbO3 modulator. The light was then injected in the silicon waveguide and absorbed in the Ge photodetector, which was directly connected to a 60GHz Tektronics sampling oscilloscope.

Open eye diagrams from germanium detectors were obtained at 10Gb/s, 20Gb/s, 30Gb/s and 40Gb/s under 0V and −1V (Fig. 4). The fact that the eye diagram was still open under zero-bias at 40Gb/s corresponds to a major milestone for low power consumption receivers.

Fig. 5 Eye diagrams at 10Gbit/s, 20Gbit/s, 30Gbit/s and 40Gbit/s under zero-bias and −1V.

4. Conclusion

We report a Ge photodetector which was selectively grown at the end of silicon waveguide. A very high optical bandwidth estimated at 120 GHz is shown, with a responsivity as high as 0.8A/W at 1550 nm. Open eye diagrams at 40Gb/s were obtained under zero-bias. These ultra-fast performances of Ge integrated photodetectors constitute a new milestone towards new generations of several Tbs/s chips merging electronic and photonic building blocks and devices.

Acknowledgments

The research leading to these results has received funding from the European Community under grant agreement no. 224312 HELIOS and from the French ANR under project MICROS.

References and links

1.

B. Ben Bakir, A. Descos, N. Olivier, D. Bordel, P. Grosse, E. Augendre, L. Fulbert, and J. M. Fedeli, “Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers,” Opt. Express 19(11), 10317–10325 (2011). [CrossRef] [PubMed]

2.

J. Liu, X. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett. 35(5), 679–681 (2010). [CrossRef] [PubMed]

3.

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]

4.

D. Marris-Morini, L. Vivien, G. Rasigade, J.-M. Fedeli, E. Cassan, X. Le Roux, P. Crozat, S. Maine, A. Lupu, P. Lyan, P. Rivallin, M. Halbwax, and S. Laval, “Recent Progress in High-Speed Silicon-Based Optical Modulators,” Proc. IEEE 97(7), 1199–1215 (2009). [CrossRef]

5.

H.-W. Chen, J. D. Peters, and J. E. Bowers, “Forty Gb/s hybrid silicon Mach-Zehnder modulator with low chirp,” Opt. Express 19(2), 1455–1460 (2011). [CrossRef] [PubMed]

6.

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]

7.

T. Tsuchizawa, K. Yamada, T. Watanabe, S. Park, H. Nishi, K. Rai, H. Shinojima, and S.-I. Itabashi, “Monolithic integration of silicon-, germanium-, and silica-based optical devices for telecommunications applications,” IEEE J. Select. Top.Quantum Electron 17(3), 516–525 (2011). [CrossRef]

8.

T. Yin, R. Cohen, M. M. Morse, G. Sarid, Y. Chetrit, D. Rubin, and M. J. Paniccia, “31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate,” Opt. Express 15(21), 13965–13971 (2007). [CrossRef] [PubMed]

9.

L. Chen, C. R. Doerr, L. Buhl, Y. Baeyens, and R. A. Aroca, “Monolithically integrated 40-wavelength demultiplexer and photodetector array on silicon,” IEEE Photonics Technol. Lett. 23(13), 869–871 (2011). [CrossRef]

10.

S. Park, T. Tsuchizawa, T. Watanabe, H. Shinojima, H. Nishi, K. Yamada, Y. Ishikawa, K. Wada, and S. Itabashi, “Monolithic integration and synchronous operation of germanium photodetectors and silicon variable optical attenuators,” Opt. Express 18(8), 8412–8421 (2010). [CrossRef] [PubMed]

11.

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]

12.

J. Wang and S. Lee, “Ge-Photodetectors for Si-Based Optoelectronic Integration,” Sensors (Basel Switzerland) 11(1), 696–718 (2011). [CrossRef]

13.

M. Jutzi, M. Berroth, G. Wohl, M. Oehme, and E. Kasper, “Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth,” IEEE Photonics Technol. Lett. 17(7), 1510–1512 (2005). [CrossRef]

14.

J.-M. Hartmann, A. Abbadie, A. M. Papon, P. Holliger, G. Rolland, T. Billon, J.-M. Fédéli, M. Rouvière, L. Vivien, and S. Laval, “Reduced pressure-chemical vapor deposition of Ge thick layers on Si(001) for 1.3-1.55-µm photodetection,” J. Appl. Phys. 95(10), 5905–5907 (2004). [CrossRef]

15.

M. Kolahdouz, L. Maresca, R. Ghandi, A. Khatibi, and H. H. Radamson, “Kinetic Model of SiGe Selective Epitaxial Growth using RPCVD Technique,” J. Electrochem. Soc. 158(4), H457 (2011). [CrossRef]

16.

J. M. Hartmann, A. Abbadie, N. Cherkashin, H. Grampeix, and L. Clavelier, “Epitaxial growth of Ge thick layers on nominal and 6° off Si(001); Ge surface passivation by Si,” Semicond. Sci. Technol. 24, 055002–055005 (2009).

17.

J. M. Hartmann, A. Abbadie, J. P. Barnes, J. M. Fédéli, T. Billon, and L. Vivien, “Impact of the H2 anneal on the structural and optical properties of thin and thick Ge layers on Si; Low temperature surface passivation of Ge by Si,” J. Cryst. Growth 312(4), 532–541 (2010). [CrossRef]

18.

G. Wang, R. Loo, E. Simoen, L. Souriau, M. Caymax, M. M. Heyns, and B. Blanpain, “A model of threading dislocation density in strain-relaxed Ge and GaAs epitaxial films on Si (100),” Appl. Phys. Lett. 94(10), 102115 (2009). [CrossRef]

19.

Y. Yamamoto, P. Zaumseil, T. Arguirov, M. Kittler, and B. Tillack, “Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD,” Solid-State Electron. 60(1), 2–6 (2011). [CrossRef]

OCIS Codes
(130.0130) Integrated optics : Integrated optics
(130.0250) Integrated optics : Optoelectronics
(250.0040) Optoelectronics : Detectors

ToC Category:
Integrated Optics

History
Original Manuscript: October 6, 2011
Revised Manuscript: November 9, 2011
Manuscript Accepted: November 9, 2011
Published: January 4, 2012

Citation
Laurent Vivien, Andreas Polzer, Delphine Marris-Morini, Johann Osmond, Jean Michel Hartmann, Paul Crozat, Eric Cassan, Christophe Kopp, Horst Zimmermann, and Jean Marc Fédéli, "Zero-bias 40Gbit/s germanium waveguide photodetector on silicon," Opt. Express 20, 1096-1101 (2012)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-20-2-1096


Sort:  Author  |  Year  |  Journal  |  Reset  

References

  1. B. Ben Bakir, A. Descos, N. Olivier, D. Bordel, P. Grosse, E. Augendre, L. Fulbert, and J. M. Fedeli, “Electrically driven hybrid Si/III-V Fabry-Pérot lasers based on adiabatic mode transformers,” Opt. Express19(11), 10317–10325 (2011). [CrossRef] [PubMed]
  2. J. Liu, X. Sun, R. Camacho-Aguilera, L. C. Kimerling, and J. Michel, “Ge-on-Si laser operating at room temperature,” Opt. Lett.35(5), 679–681 (2010). [CrossRef] [PubMed]
  3. 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. Express19(12), 11507–11516 (2011). [CrossRef] [PubMed]
  4. D. Marris-Morini, L. Vivien, G. Rasigade, J.-M. Fedeli, E. Cassan, X. Le Roux, P. Crozat, S. Maine, A. Lupu, P. Lyan, P. Rivallin, M. Halbwax, and S. Laval, “Recent Progress in High-Speed Silicon-Based Optical Modulators,” Proc. IEEE97(7), 1199–1215 (2009). [CrossRef]
  5. H.-W. Chen, J. D. Peters, and J. E. Bowers, “Forty Gb/s hybrid silicon Mach-Zehnder modulator with low chirp,” Opt. Express19(2), 1455–1460 (2011). [CrossRef] [PubMed]
  6. 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. Express17(8), 6252–6257 (2009). [CrossRef] [PubMed]
  7. T. Tsuchizawa, K. Yamada, T. Watanabe, S. Park, H. Nishi, K. Rai, H. Shinojima, and S.-I. Itabashi, “Monolithic integration of silicon-, germanium-, and silica-based optical devices for telecommunications applications,” IEEE J. Select. Top.Quantum Electron17(3), 516–525 (2011). [CrossRef]
  8. T. Yin, R. Cohen, M. M. Morse, G. Sarid, Y. Chetrit, D. Rubin, and M. J. Paniccia, “31 GHz Ge n-i-p waveguide photodetectors on Silicon-on-Insulator substrate,” Opt. Express15(21), 13965–13971 (2007). [CrossRef] [PubMed]
  9. L. Chen, C. R. Doerr, L. Buhl, Y. Baeyens, and R. A. Aroca, “Monolithically integrated 40-wavelength demultiplexer and photodetector array on silicon,” IEEE Photonics Technol. Lett.23(13), 869–871 (2011). [CrossRef]
  10. S. Park, T. Tsuchizawa, T. Watanabe, H. Shinojima, H. Nishi, K. Yamada, Y. Ishikawa, K. Wada, and S. Itabashi, “Monolithic integration and synchronous operation of germanium photodetectors and silicon variable optical attenuators,” Opt. Express18(8), 8412–8421 (2010). [CrossRef] [PubMed]
  11. 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. Express19(11), 10967–10972 (2011). [CrossRef] [PubMed]
  12. J. Wang and S. Lee, “Ge-Photodetectors for Si-Based Optoelectronic Integration,” Sensors (Basel Switzerland)11(1), 696–718 (2011). [CrossRef]
  13. M. Jutzi, M. Berroth, G. Wohl, M. Oehme, and E. Kasper, “Ge-on-Si vertical incidence photodiodes with 39-GHz bandwidth,” IEEE Photonics Technol. Lett.17(7), 1510–1512 (2005). [CrossRef]
  14. J.-M. Hartmann, A. Abbadie, A. M. Papon, P. Holliger, G. Rolland, T. Billon, J.-M. Fédéli, M. Rouvière, L. Vivien, and S. Laval, “Reduced pressure-chemical vapor deposition of Ge thick layers on Si(001) for 1.3-1.55-µm photodetection,” J. Appl. Phys.95(10), 5905–5907 (2004). [CrossRef]
  15. M. Kolahdouz, L. Maresca, R. Ghandi, A. Khatibi, and H. H. Radamson, “Kinetic Model of SiGe Selective Epitaxial Growth using RPCVD Technique,” J. Electrochem. Soc.158(4), H457 (2011). [CrossRef]
  16. J. M. Hartmann, A. Abbadie, N. Cherkashin, H. Grampeix, and L. Clavelier, “Epitaxial growth of Ge thick layers on nominal and 6° off Si(001); Ge surface passivation by Si,” Semicond. Sci. Technol.24, 055002–055005 (2009).
  17. J. M. Hartmann, A. Abbadie, J. P. Barnes, J. M. Fédéli, T. Billon, and L. Vivien, “Impact of the H2 anneal on the structural and optical properties of thin and thick Ge layers on Si; Low temperature surface passivation of Ge by Si,” J. Cryst. Growth312(4), 532–541 (2010). [CrossRef]
  18. G. Wang, R. Loo, E. Simoen, L. Souriau, M. Caymax, M. M. Heyns, and B. Blanpain, “A model of threading dislocation density in strain-relaxed Ge and GaAs epitaxial films on Si (100),” Appl. Phys. Lett.94(10), 102115 (2009). [CrossRef]
  19. Y. Yamamoto, P. Zaumseil, T. Arguirov, M. Kittler, and B. Tillack, “Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD,” Solid-State Electron.60(1), 2–6 (2011). [CrossRef]

Cited By

Alert me when this paper is cited

OSA is able to provide readers links to articles that cite this paper by participating in CrossRef's Cited-By Linking service. CrossRef includes content from more than 3000 publishers and societies. In addition to listing OSA journal articles that cite this paper, citing articles from other participating publishers will also be listed.

Figures

Fig. 1 Fig. 2 Fig. 3
 
Fig. 4 Fig. 5
 

« Previous Article  |  Next Article »

OSA is a member of CrossRef.

CrossCheck Deposited