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Optics Express

Optics Express

  • Editor: Michael Duncan
  • Vol. 14, Iss. 18 — Sep. 4, 2006
  • pp: 8154–8159
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Laser emission and photodetection in an InP/InGaAsP layer integrated on and coupled to a Silicon-on-Insulator waveguide circuit

G. Roelkens, D. Van Thourhout, R. Baets, R. Nötzel, and M. Smit  »View Author Affiliations


Optics Express, Vol. 14, Issue 18, pp. 8154-8159 (2006)
http://dx.doi.org/10.1364/OE.14.008154


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Abstract

Laser emission from an InP/InGaAsP thin film epitaxial layer bonded to a Silicon-on-Insulator waveguide circuit was observed. Adhesive bonding using divinyl-tetramethyldisiloxane-benzocyclobutene (DVS-BCB) was used to integrate the InP/InGaAsP epitaxial layers onto the waveguide circuit. Light is coupled from the laser diode into an underlying waveguide using an adiabatic inverted taper approach. 0.9mW optical power was coupled into the SOI waveguide using a 500μm long laser. Besides for use as a laser diode, the same type of devices can be used as a photodetector. 50μm long devices obtained a responsivity of 0.23A/W.

© 2006 Optical Society of America

1. Introduction

Silicon-on-Insulator (SOI) is gaining importance for the fabrication of ultra-compact photonic integrated circuits, due to the high refractive index contrast between Silicon core (n=3.45) and SiO2 cladding (n=1.45). Moreover, standard CMOS technology for the fabrication of the devices can be used increasing the yield, reproducibility and economy of scale of the fabricated devices [1

1 . W. Bogaerts , R. Baets , P. Dumon , V. Wiaux , S. Beckx , D. Taillaert , B. Luyssaert , J. Van Campenhout , P. Bienstman , and D. Van Thourhout , “ Nanophotonic waveguides in silicon-on-insulator fabricated with CMOS technology ,” J. Lightwave Technol. 23 , 401 – 412 ( 2005 ). [CrossRef]

]. Low loss nanophotonic waveguides are obtained and very compact optical functions (ring resonators, arrayed waveguide gratings,…) have been realized [2

2 . P. Dumon , W. Bogaerts , V. Wiaux , J. Wouters , S. Beckx , J. Van Campenhout , D. Taillaert , B. Luyssaert , P. Bienstman , D. Van Thourhout , and R. Baets , “ Low-loss SOI photonic wires and ring resonators fabricated with deep UV lithography ,” Photon. Technol. Lett. 16 , 1328 – 1331 ( 2004 ). [CrossRef]

], [3

3 . K. Sasaki , F. Ohno , A. Motegi , and T. Baba , “ Arrayed waveguide grating of 70×60 μm 2 size based on Si photonic wire waveguides ,” Electron. Lett. 41 , 801 – 802 ( 2005 ). [CrossRef]

]. As Silicon has an indirect bandgap, electrically pumped laser diodes have not yet been achieved, despite significant work in the field of Silicon photonics [4

4 . S. G. Cloutier , P. A. Kossyrev , and J. Xu , “ Optical gain and stimulated emission in periodic nanopatterned crystalline silicon ,” Nat. Mat. 4 , 887 – 891 ( 2005 ). [CrossRef]

], [5

5 . R. Jones , H. S. Rong , A. S. Liu , A. W. Fang , M. J. Paniccia , D. Hak , and O. Cohen , “ Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering ,” Opt. Express 13 , 519 – 525 ( 2005 ). [CrossRef] [PubMed]

]. The integration of direct bandgap III-V semiconductor layers (and more in particular InP/InGaAsP epitaxial layer structures for laser emission at 1.55μm) on top of the SOI waveguide circuits is therefore the most straightforward way to achieve electrically pumped laser emission and coupling to an SOI waveguide. Moreover, as Silicon is transparent for wavelengths above 1.1μm, it cannot be used for light detection at telecommunication wavelengths. To overcome this problem, the epitaxial growth of Germanium on top of the Silicon waveguide core is being investigated [6

6 . L. Colace , G. Masini , and G. Assanto , “ Ge-on-Si approaches to the detection of near-infrared light ,” J. Quantum Electron. 35 , 1843 – 1850 ( 1999 ). [CrossRef]

]. However, we will show here that using the same type of InP/InGaAsP layer structure and the same processing steps, one can also fabricate III-V photodetectors for telecommunication wavelengths integrated on top of SOI waveguide circuits.

2. Integration of InP/InGaAsP layers on top of Silicon-on-Insulator

There are different approaches to integrate III-V layers on a Silicon-on-Insulator substrate. Hetero-epitaxial growth results in large threading and misfit dislocation densities due to the large mismatch in lattice constants of the two material systems. The occurrence of these large dislocations densities in the active region can be overcome for example by epitaxial lateral overgrowth [7

7 . O. Parillaud , E. GilLafon , B. Gerard , P. Etienne , and D. Pribat , “ High quality InP on Si by conformal growth ,” Appl. Phys. Lett. 68 , 2654 – 2656 ( 1996 ). [CrossRef]

], by using the strain field induced by quantum dots to prevent the dislocation from reaching the optically active region [8

8 . Z. Mi , J. Yang , P. Bhattacharya , and D. L. Huffaker , “ Self-organised quantum dots as dislocation filters: the case of GaAs-based lasers on silicon ,” Electron. Lett. 42 , 121 – 122 ( 2006 ). [CrossRef]

] or by using buffer layers [9

9 . R. Droopad , J. Curless , Z. Yu , D. Jordan , Y. Liang , C. Overgaard , H. Li , T. Eschrich , J. Ramdani , and L. Hilt , “ GaAs on silicon using an oxide buffer layer ,” Compound Semiconductors 174 , 1 – 5 ( 2003 ).

]. Although significant progress is being made in the field, the epitaxial layer quality is still lower compared to layers grown on a lattice matched substrate. To circumvent the problem of epitaxial layer quality, wafer bonding techniques can be used to integrate high quality InP/InGaAsP layer structures on a Silicon substrate. In [10

10 . H. Park , A. W. Fang , S. Kodama , and J. E. Bowers , “ Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum well ,” Optics Express 13 , 9460 – 9464 ( 2005 ). [CrossRef] [PubMed]

] a low temperature O2 plasma-assisted direct wafer bonding process was used to bond AlGaInAs quantum well heterostructures onto a processed Silicon-on-Insulator waveguide substrate. Laser diodes were fabricated by cleaving the devices and were optically pumped. Here, we present the use of an adhesive bonding process using divinyl-tetramethyldisiloxane-benzocyclobutene (DVS-BCB) [11

11 . F. Niklaus , P. Enoksson , E. Kalvesten , and G. Stemme , “ Low temperature full wafer adhesive bonding of structured wafers ,” J. Micromech. Microeng. 11 , 100 – 111 ( 2001 ). [CrossRef]

] to create, to our knowledge, the first electrically injected thin film InP/InGaAsP laser diode integrated on and coupled to a Silicon-on-Insulator waveguide circuit.

3. DVS-BCB adhesive bonding

DVS-BCB was used to bond an InP/InGaAsP epitaxial layer structure grown on an InP substrate, epitaxial layers down onto a processed SOI substrate. The SOI substrate consists of a 220nm thick Silicon waveguide core layer on a 1μm SiO2 buffer layer. The SOI waveguides are formed by etching through the Silicon waveguide layer, leaving a topology of 220nm height on the SOI surface. After cleaning the SOI wafer using 3H2SO4:1H2O2 and 1NH3:4H2O2:20H2O to remove the hydrocarbon contamination and particles that are pinned to the surface respectively, two layers of DVS-BCB were spin coated on the surface to achieve an aggregate bonding layer thickness of 300nm. This double coating process was used to obtain a degree of planarization of the spin coating process above 90 percent. After spin coating, the DVS-BCB is partially cured for 2min at 250C to transform the liquid DVS-BCB into a sol/gel rubber. This is done in a nitrogen environment to prevent the oxidation of the DVS-BCB. Subsequently, InP/InGaAsP dies are bonded to the SOI substrate in a vacuum environment to prevent the inclusion of air at the bonding interface. The wafer stack is cured at 250C for 1 hour in a nitrogen environment to completely polymerize the DVS-BCB. A pressure of 300kPa is applied during curing to obtain an intimate contact between both wafer surfaces. After bonding, the original InP substrate is removed using a combination of mechanical grinding and wet etching using 3HCl:H2O, until an InGaAs etch stop layer is reached. This leaves the InP/InGaAsP epitaxial layer stack attached to the SOI waveguide circuit as is shown in figure 1.

Fig.1. Cross section of the bonding interface after InP substrate removal.

4. Coupling between SOI and InP/InGaAsP

In order to efficiently couple light between the InP/InGaAsP active layer and the SOI waveguide circuit, a coupling scheme based on an inverted adiabatic taper was used as shown in Fig. 2. The inverted taper adiabatically transforms the SOI waveguide mode to the fundamental mode of a polymer waveguide, which lies on top of the inverted taper and is butt coupled to the InP/InGaAsP active layer. The design parameters of the inverted taper structure are shown in Fig. 3. The polymer waveguide consists of a polyimide waveguide core (n=1.67) surrounded by a DVS-BCB (n=1.54) cladding layer, which is not drawn for clarity. This type of coupling structure has been shown to result in a high efficiency and large optical bandwidth coupling [12

12 . G. Roelkens , P. Dumon , W. Bogaerts , D. Van Thourhout , and R. Baets , “ Efficient silicon-on-insulator fiber coupler fabricated using 248-nm-deep UV lithography ,” Photon. Technol. Lett. 17 , 2613 – 2615 ( 2005 ). [CrossRef]

].

Fig. 2. Coupling scheme to couple light from an SOI waveguide to the InP/InGaAsP waveguide layer.
Fig. 3. Design parameters for the adiabatic inverted taper structure.

The InP/InGaAsP layer stack consists of a 600nm n-type InP undercladding, six InGaAsP quantum wells with a bandgap wavelength of 1550nm in between two separate confinement layers of 150nm (bandgap wavelength 1.25μm) and a 2μm p-type InP and 150nm p++ InGaAs contact layer.

The polyimide waveguide core height was designed for an optimal coupling between the fundamental III-V waveguide mode and the polymer waveguide mode. The coupling efficiency is plotted in figure 4. Calculations were based on a 3 dimensional fully vectorial eigenmode expansion method. A coupling loss of 1.4dB is obtained at an optimum polyimide waveguide height of 1.3μm. About 0.6dB is due to the reflection at the polymer/III-V interface.

Fig. 4. Butt coupling efficiency at the polymer/III-V interface as a function of polyimide waveguide core height.

5. Fabrication of devices

Fig. 5. Fabrication sequence of electrically injected thin film laser diodes and thin film photodetectors.
Fig. 6. Top view of a fabricated device.

6. Characterization

Fig. 7. Detected power versus injected current for a 500 μm long laser cavity.

Fig. 8. Voltage versus current characteristics for a 50μm long photodetector with and without illumination.

7. Conclusion

For the first time electrically injected thin film laser diodes and thin film photodetectors were integrated on and coupled to a Silicon-on-Insulator waveguide circuit. This type of integration paves the way to more complex optical functionalities based on the advantages of passive Silicon-on-Insulator waveguide circuits and active III-V devices.

Acknowledgments

This work was partly supported by the European union through the IST-PICMOS project, the Network of Excellence ePIXnet, by the Belgian IAP-PHOTON network, the IWT-GBOU project Plastic Photonics, IWT-SBO epSOC and the Fund for Scientific Research (FWO).

References and Links

1 .

W. Bogaerts , R. Baets , P. Dumon , V. Wiaux , S. Beckx , D. Taillaert , B. Luyssaert , J. Van Campenhout , P. Bienstman , and D. Van Thourhout , “ Nanophotonic waveguides in silicon-on-insulator fabricated with CMOS technology ,” J. Lightwave Technol. 23 , 401 – 412 ( 2005 ). [CrossRef]

2 .

P. Dumon , W. Bogaerts , V. Wiaux , J. Wouters , S. Beckx , J. Van Campenhout , D. Taillaert , B. Luyssaert , P. Bienstman , D. Van Thourhout , and R. Baets , “ Low-loss SOI photonic wires and ring resonators fabricated with deep UV lithography ,” Photon. Technol. Lett. 16 , 1328 – 1331 ( 2004 ). [CrossRef]

3 .

K. Sasaki , F. Ohno , A. Motegi , and T. Baba , “ Arrayed waveguide grating of 70×60 μm 2 size based on Si photonic wire waveguides ,” Electron. Lett. 41 , 801 – 802 ( 2005 ). [CrossRef]

4 .

S. G. Cloutier , P. A. Kossyrev , and J. Xu , “ Optical gain and stimulated emission in periodic nanopatterned crystalline silicon ,” Nat. Mat. 4 , 887 – 891 ( 2005 ). [CrossRef]

5 .

R. Jones , H. S. Rong , A. S. Liu , A. W. Fang , M. J. Paniccia , D. Hak , and O. Cohen , “ Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering ,” Opt. Express 13 , 519 – 525 ( 2005 ). [CrossRef] [PubMed]

6 .

L. Colace , G. Masini , and G. Assanto , “ Ge-on-Si approaches to the detection of near-infrared light ,” J. Quantum Electron. 35 , 1843 – 1850 ( 1999 ). [CrossRef]

7 .

O. Parillaud , E. GilLafon , B. Gerard , P. Etienne , and D. Pribat , “ High quality InP on Si by conformal growth ,” Appl. Phys. Lett. 68 , 2654 – 2656 ( 1996 ). [CrossRef]

8 .

Z. Mi , J. Yang , P. Bhattacharya , and D. L. Huffaker , “ Self-organised quantum dots as dislocation filters: the case of GaAs-based lasers on silicon ,” Electron. Lett. 42 , 121 – 122 ( 2006 ). [CrossRef]

9 .

R. Droopad , J. Curless , Z. Yu , D. Jordan , Y. Liang , C. Overgaard , H. Li , T. Eschrich , J. Ramdani , and L. Hilt , “ GaAs on silicon using an oxide buffer layer ,” Compound Semiconductors 174 , 1 – 5 ( 2003 ).

10 .

H. Park , A. W. Fang , S. Kodama , and J. E. Bowers , “ Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum well ,” Optics Express 13 , 9460 – 9464 ( 2005 ). [CrossRef] [PubMed]

11 .

F. Niklaus , P. Enoksson , E. Kalvesten , and G. Stemme , “ Low temperature full wafer adhesive bonding of structured wafers ,” J. Micromech. Microeng. 11 , 100 – 111 ( 2001 ). [CrossRef]

12 .

G. Roelkens , P. Dumon , W. Bogaerts , D. Van Thourhout , and R. Baets , “ Efficient silicon-on-insulator fiber coupler fabricated using 248-nm-deep UV lithography ,” Photon. Technol. Lett. 17 , 2613 – 2615 ( 2005 ). [CrossRef]

13 .

I. Christiaens , G. Roelkens , K. De Mesel , D. Van Thourhout , and R. Baets , “ Thin-film devices fabricated with benzocyclobutene adhesive wafer bonding ,” J. Lightwave Technol. 23 , 517 – 523 ( 2005 ). [CrossRef]

OCIS Codes
(130.0130) Integrated optics : Integrated optics
(220.4610) Optical design and fabrication : Optical fabrication

ToC Category:
Integrated Optics

History
Original Manuscript: June 19, 2006
Manuscript Accepted: August 1, 2006
Published: September 1, 2006

Citation
G. Roelkens, D. Van Thourhout, R. Baets, R. Nötzel, and M. Smit, "Laser emission and photodetection in an InP/InGaAsP layer integrated on and coupled to a Silicon-on-Insulator waveguide circuit," Opt. Express 14, 8154-8159 (2006)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-14-18-8154


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References

  1. W. Bogaerts, R. Baets, P. Dumon, V. Wiaux, S. Beckx, D. Taillaert, B. Luyssaert, J. Van Campenhout, P. Bienstman, and D. Van Thourhout," Nanophotonic waveguides in silicon-on-insulator fabricated with CMOS technology," J. Lightwave Technol. 23, 401-412 (2005). [CrossRef]
  2. P. Dumon, W. Bogaerts, V. Wiaux, J. Wouters, S. Beckx, J. Van Campenhout, D. Taillaert, B. Luyssaert, P. Bienstman, D. Van Thourhout, and R. Baets, "Low-loss SOI photonic wires and ring resonators fabricated with deep UV lithography," Photon. Technol. Lett. 16, 1328-1331 (2004). [CrossRef]
  3. K. Sasaki, F. Ohno, A. Motegi, and T. Baba, "Arrayed waveguide grating of 70x60 μm2 size based on Si photonic wire waveguides," Electron. Lett. 41, 801-802 (2005). [CrossRef]
  4. S. G. Cloutier, P. A. Kossyrev, and J. Xu, "Optical gain and stimulated emission in periodic nanopatterned crystalline silicon," Nat. Mat. 4, 887-891 (2005). [CrossRef]
  5. R. Jones, H. S. Rong, A. S. Liu, A. W. Fang, M. J. Paniccia, D. Hak, and O. Cohen, "Net continuous wave optical gain in a low loss silicon-on-insulator waveguide by stimulated Raman scattering," Opt. Express 13, 519-525 (2005). [CrossRef] [PubMed]
  6. L. Colace, G. Masini, and G. Assanto, "Ge-on-Si approaches to the detection of near-infrared light," J. Quantum Electron. 35, 1843-1850 (1999). [CrossRef]
  7. O. Parillaud, E. GilLafon, B. Gerard, P. Etienne, and D. Pribat, "High quality InP on Si by conformal growth," Appl. Phys. Lett. 68, 2654 -2656 (1996). [CrossRef]
  8. Z. Mi, J. Yang, P. Bhattacharya, and D. L. Huffaker, "Self-organised quantum dots as dislocation filters: the case of GaAs-based lasers on silicon," Electron. Lett. 42, 121-122 (2006). [CrossRef]
  9. R. Droopad, J. Curless, Z. Yu, D. Jordan, Y. Liang, C. Overgaard, H. Li, T. Eschrich, J. Ramdani, and L. Hilt, "GaAs on silicon using an oxide buffer layer," Compound Semiconductors 174, 1-5 (2003).
  10. H. Park, A. W. Fang, S. Kodama, and J. E. Bowers, "Hybrid silicon evanescent laser fabricated with a silicon waveguide and III-V offset quantum well,"Optics Express 13, 9460-9464 (2005). [CrossRef] [PubMed]
  11. F. Niklaus, P. Enoksson, E. Kalvesten, and G. Stemme, "Low temperature full wafer adhesive bonding of structured wafers," J. Micromech. Microeng. 11, 100-111 (2001). [CrossRef]
  12. G. Roelkens, P. Dumon, W. Bogaerts, D. Van Thourhout, and R. Baets, "Efficient silicon-on-insulator fiber coupler fabricated using 248-nm-deep UV lithography," Photon. Technol. Lett. 17, 2613-2615 (2005). [CrossRef]
  13. I. Christiaens, G. Roelkens, K. De Mesel, D. Van Thourhout, and R. Baets, "Thin-film devices fabricated with benzocyclobutene adhesive wafer bonding," J. Lightwave Technol. 23, 517-523 (2005). [CrossRef]

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