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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 18, Iss. 13 — Jun. 21, 2010
  • pp: 13945–13950
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Room-temperature electroluminescence from Si microdisks with Ge quantum dots

Jinsong Xia, Yuuki Takeda, Noritaka Usami, Takuya Maruizumi, and Yasuhiro Shiraki  »View Author Affiliations


Optics Express, Vol. 18, Issue 13, pp. 13945-13950 (2010)
http://dx.doi.org/10.1364/OE.18.013945


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Abstract

A current-injected silicon-based light-emitting device was fabricated on silicon-on-insulator (SOI) by embedding Ge self-assembled quantum dots into a silicon microdisk resonator with p-i-n junction for current-injection. Room-temperature resonant electroluminescence (EL) from Ge self-assembled quantum dots in the microdisk was successfully observed under current injection, and observed EL peaks corresponding to the whispering gallery modes (WGMs) supported by the microdisk resonator were well identified by means of numerical simulations.

© 2010 OSA

1. Introduction

Si-based light-emitting devices are one of the important components for hybrid optoelectronic integration on Si platform. Various solutions have been proposed in recent years in order to enhance the light emission from Si-based materials. Quantum structures including quantum wells and dots [1

1. D. K. Nayak, N. Usami, S. Fukatsu, and Y. Shiraki, “Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100),” Appl. Phys. Lett. 63(25), 3509–3511 (1993). [CrossRef]

4

4. S. Fukatsu, H. Sunamuru, Y. Shiraki, and S. Komiyama, “Phononless radiative recombination of indirect excitons in a Si/Ge type-II quantum dot,” Appl. Phys. Lett. 71(2), 258–261 (1997). [CrossRef]

], Si nanocrystals [5

5. L. Pavesi, L. Dal Negro, C. Mazzoleni, G. Franzò, and F. Priolo, “Optical gain in silicon nanocrystals,” Nature 408(6811), 440–444 (2000). [CrossRef] [PubMed]

,6

6. L. Dal Negro, M. Cazzanelli, L. Pavesi, S. Ossicini, D. Pacifici, G. Franzò, F. Priolo, and F. Iacona, “Dynamics of stimulated emission in silicon nanocrystals,” Appl. Phys. Lett. 82(26), 4636–4638 (2003). [CrossRef]

], Er doping [7

7. G. Franzò, F. Priolo, S. Coffa, A. Polman, and A. Camera, “Room-temperature electroluminescence from Er‐doped crystalline Si,” Appl. Phys. Lett. 64(17), 2235–2237 (1994). [CrossRef]

,8

8. D. Pacifici, G. Franzò, F. Priolo, F. Iacona, and L. D. Negro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys.Rev.B 67, 245301–1-245301–13 (2003). [CrossRef]

], and defects engineering [9

9. A. A. Shklyaev, Y. Nakamura, F. N. Dultsev, and M. Ichikawa, “Defect-related light emission in the 1.4-1.7μm range from Si layers at room temperature,” J. Appl. Phys. 105, 063513–1-063513–4 (2009).

,10

10. J. Bao, M. Tabbal, T. Kim, S. Charnvanichborikarn, J. S. Williams, M. J. Aziz, and F. Capasso, “Point defect engineered Si sub-bandgap light-emitting diode,” Opt. Express 15(11), 6727–6733 (2007). [CrossRef] [PubMed]

] have been proposed for creating light-emitting centers in Si or Si-based materials. Ge self-assembled quantum dots are another possible choice for Si-based light-emitting devices [3

3. K. Kawaguchi, M. Morooka, K. Konishi, S. Koh, and Y. Shiraki, “Optical properties of strain-balanced SiGe planar microcavities with Ge dots on Si substrates,” Appl. Phys. Lett. 81(5), 817–819 (2002). [CrossRef]

,4

4. S. Fukatsu, H. Sunamuru, Y. Shiraki, and S. Komiyama, “Phononless radiative recombination of indirect excitons in a Si/Ge type-II quantum dot,” Appl. Phys. Lett. 71(2), 258–261 (1997). [CrossRef]

]. The advantages of Ge self-assembled quantum dots are the compatibility to complimentary metal oxide semiconductor (CMOS) technology and the light emission at telecommunication wavelengths. Ge dots emit light in the wavelength range of 1.3-1.6 µm and Si is transparent for the light in this range, which is important for the future integration of Si waveguide circuits and Si-based light-emitting devices on a single Si wafer. Optoelectronic hybrid integration based on Ge dots-based light source is therefore a potential direction if practical Ge dots-based light-emitting devices are available. However, light emission from Ge self-assembled quantum dots is still lack of efficiency and spectrum purity is poor. In order to enhance the light emission, embedding Ge self-assembled quantum dots into microcavities such as photonic crystal cavities [11

11. J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102–1-201102–3 (2006).

,12

12. “M. El kurdi, S. David, P. Boucard, C. Kammerer, X. Li, V. Le Thanh, and S Sauvage, “Strong 1.3–1.5 μm luminescence from Ge/Si self-assembled islands in highly confining microcavities on silicon on insulator,” J. Appl. Phys. 96, 997–1000 (2004). [CrossRef]

] and microdisk resonators [13

13. J. S. Xia, K. Nemoto, Y. Ikegami, and Y. Shiraki, “Silicon-based light emitters fabricated by embedding Ge self-assembled quantum dots in microdisks,” Appl. Phys. Lett. 91, 011104–1-011104–3 (2007). [CrossRef] [PubMed]

] has been reported and strong room-temperature resonant photoluminescence has been observed from the microcavities. A quality factor as high as 20 000 has been also achieved for the resonant light emission from Ge dots in photonic crystal L3 cavities [14

14. M. El Kurdi, X. Checoury, S. David, T. P. Ngo, N. Zerounian, P. Boucaud, O. Kermarrec, Y. Campidelli, and D. Bensahel, “Quality factor of Si-based photonic crystal L3 nanocavities probed with an internal source,” Opt. Express 16(12), 8780–8791 (2008). [CrossRef] [PubMed]

]. These progresses show that Ge dots in optical microcavities is a possible choice for Si-based light sources. To develop practical devices, however, current-injection should be realized in such Ge dots-based light-emitting devices. Although there are some reports on electroluminescence SiGe heterostructures [15

15. S. Fukatsu, N. Usami, T. Chinzei, Y. Shiraki, A. Nishida, and K. Nakagawa, “Electroluminescence from Strained SiGe/Si Quantum Well Structures Grown by Solid Source Si Molecular Beam Epitaxy,” Jpn. J. Appl. Phys. 31(Part 2, No. 8A), L1015–L1017 (1992). [CrossRef]

,16

16. T. Brunhes, P. Boucaud, S. Sauvage, F. Aniel, J.-M. Lourtioz, C. Hernandez, Y. Campidelli, O. Kermarrec, D. Bensahel, G. Faini, and I. Sagnes, “Electroluminescence of Ge/Si self-assembled quantum dots grown by chemical vapor deposition,” Appl. Phys. Lett. 77(12), 1822–1824 (2000). [CrossRef]

], there are few reports on the study of electroluminescence from Ge dots in optical microcavities. In this paper, we report the research on the Si-based light-emitting device based on Ge quantum dots in a microdisk resonator with p-i-n junction for current-injection.

2. Device fabrication

Figure 1
Fig. 1 Cross-section view of the structure of the current-injected light-emitting device.
shows the schematic structure of the fabricated current-injected Si-based light-emitting device. Ge self-assembled quantum dots are embedded into a Si microdisk resonator on silicon-on-insulator (SOI) with a vertical p-i-n junction for current-injection. Under forward bias, the current flows to the microdisk from the surrounding p + area through the thin Si film on the buried oxide. After going through multiple Ge dots layers, the current is collected by the top n + layer. The thickness of the top Si film and buried oxide of the SOI wafer were 260 nm and 2 µm, respectively. As the internal light-emitting centers, multiple layers of Ge self-assembled quantum dots were grown on p-type SOI by solid-source molecular beam epitaxy (SSMBE) at 600°C. In order to enhance the total number of Ge dots in the devices, ten layers of the Ge self-assembled quantum dots were grown with 15-nm-thick Si spacer layers and an 80-nm-thick Si cap layer. To fabricate the vertical p-i-n junction for current-injection, As+ ions were implanted into the top Si film at an energy of 25 keV and with a dose of 1 × 1014/cm2 for the n+ layer. Electron beam lithography (EBL) was used to define silicon microdisk resonators on the sample. The top SiGe layer was etched by reactive ion etching (RIE) to form the microdisk resonator. The etching was controlled to remain a 160-nm-thick p-type Si film which works as the current pathway from the p + area. Selective B+ ion-implantation was performed in the surrounding sector windows defined by EBL to form the p + area. The energy and dose of the ions were 25 keV and 1 × 1015/cm2, respectively. The sample was annealed at 600°C for 30 minutes in N2 ambient to activate implanted dopants. After annealing, the surface of the devices was passivated with SiO2 films grown by plasma-enhanced chemical vapor deposition (PECVD). The contact window for n + area was located at the centre of the microdisk, while the contact window for p + was located in the surrounding area. Aluminum was used as contact metal. Finally, the sample was annealed at 350°C for 10 minutes in forming gas ambient.

Figure 2
Fig. 2 Scanning electron microscope image of the fabricated 2.8 µm microdisk device.
shows the scanning electronic microscope (SEM) image of the fabricated device. The size of the microdisk resonator is 2.8 µm in diameter and it is seen that the device structure is well defined by the fabrication process. Figure 3
Fig. 3 I-V characteristic of the p-i-n junction.
shows the I-V characteristic of the device. A typical curve of pn junctions is seen to be obtained. The reverse current at −5 V is 60 µA. Electroluminescent light at room-temperature was collected by a 100 × objective lens and directed into a monochromator with a 32-cm focus length. Dispersed signal was detected by a liquid nitrogen cooled multichannel InGaAs detector.

3. Results and discussion

It is noted that the wavelength range of the electroluminescence is blue shifted compared with photoluminescence spectra recorded from optical microcavities with Ge dots [11

11. J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102–1-201102–3 (2006).

13

13. J. S. Xia, K. Nemoto, Y. Ikegami, and Y. Shiraki, “Silicon-based light emitters fabricated by embedding Ge self-assembled quantum dots in microdisks,” Appl. Phys. Lett. 91, 011104–1-011104–3 (2007). [CrossRef] [PubMed]

]. The possible reason for this blue shift is the interdiffusion of Ge atoms during high temperature processes, such as dopant activation anneal and PECVD deposition of SiO2. The interdiffusion of Ge atoms in Ge dots with surrounding Si atoms causes the increase of bandgap energy of the dots. The light emission around 1.1 µm can be assigned to Si bulk bandgap transition.

Figure 5
Fig. 5 Electroluminescence spectra at different currents. The inset shows the red shift of the resonant peak against injected current.
shows the EL spectra at different currents. As well seen in the inset of the figure, the red shift of the resonant peaks is noticed against the injected current. This can be attributed to the increase of the refractive index of Si due to the thermo-optic effect induced by the current heating. Figure 6
Fig. 6 Dependence of integrated electroluminescence intensity on the injected current.
shows the current dependence of the integrated EL intensity. The observed nonlinear increase of the integrated intensity is very similar to the PL result, i.e., the PL intensity of photonic crystal microcavities with Ge self-assembled quantum dots nonlinearly increases against the excitation power [11

11. J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102–1-201102–3 (2006).

]. The possible reason for this nonlinear increase is the confining of carriers inside the microdisk. When the current is increased, local electron-hole plasma with high density tends to appear inside the disk, which leads to an additional scattering mechanism contributing to the nonlinear increase of radiative recombination.

4. Conclusion

In summary, a current-injected light-emitting device based on microdisk resonator with Ge quantum dots was fabricated on SOI and room-temperature electroluminescence was successfully observed under DC currents. Resonant peaks corresponding to the WGMs were well identified with the aid of FDTD simulations. The result shows a possible means to develop Si-based light-emitting devices for the optoelectronic integration on Si platform.

Acknowledgement

This work was partly supported by project for strategic advancement of research infrastructure for private universities, 2009–2013, and by Grant-in-Aid for Scientific Research (A) (Grant No. 21246003) from MEXT, Japan. The authors would like to thank K. Sawano, S. Iwamoto, and S. Taguchi for the discussion and help in the experiments.

References and links

1.

D. K. Nayak, N. Usami, S. Fukatsu, and Y. Shiraki, “Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100),” Appl. Phys. Lett. 63(25), 3509–3511 (1993). [CrossRef]

2.

S. Fukatsu, N. Usami, Y. Kato, H. Sunamura, Y. Shiraki, H. Oku, T. Ohnishi, Y. Ohmori, and K. Okumura, “Gas-source molecular beam epitaxy and luminescence characterization of strained Si1-xGex/Si quantum wells,” J. Cryst. Growth 136(1-4), 315–321 (1994). [CrossRef]

3.

K. Kawaguchi, M. Morooka, K. Konishi, S. Koh, and Y. Shiraki, “Optical properties of strain-balanced SiGe planar microcavities with Ge dots on Si substrates,” Appl. Phys. Lett. 81(5), 817–819 (2002). [CrossRef]

4.

S. Fukatsu, H. Sunamuru, Y. Shiraki, and S. Komiyama, “Phononless radiative recombination of indirect excitons in a Si/Ge type-II quantum dot,” Appl. Phys. Lett. 71(2), 258–261 (1997). [CrossRef]

5.

L. Pavesi, L. Dal Negro, C. Mazzoleni, G. Franzò, and F. Priolo, “Optical gain in silicon nanocrystals,” Nature 408(6811), 440–444 (2000). [CrossRef] [PubMed]

6.

L. Dal Negro, M. Cazzanelli, L. Pavesi, S. Ossicini, D. Pacifici, G. Franzò, F. Priolo, and F. Iacona, “Dynamics of stimulated emission in silicon nanocrystals,” Appl. Phys. Lett. 82(26), 4636–4638 (2003). [CrossRef]

7.

G. Franzò, F. Priolo, S. Coffa, A. Polman, and A. Camera, “Room-temperature electroluminescence from Er‐doped crystalline Si,” Appl. Phys. Lett. 64(17), 2235–2237 (1994). [CrossRef]

8.

D. Pacifici, G. Franzò, F. Priolo, F. Iacona, and L. D. Negro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys.Rev.B 67, 245301–1-245301–13 (2003). [CrossRef]

9.

A. A. Shklyaev, Y. Nakamura, F. N. Dultsev, and M. Ichikawa, “Defect-related light emission in the 1.4-1.7μm range from Si layers at room temperature,” J. Appl. Phys. 105, 063513–1-063513–4 (2009).

10.

J. Bao, M. Tabbal, T. Kim, S. Charnvanichborikarn, J. S. Williams, M. J. Aziz, and F. Capasso, “Point defect engineered Si sub-bandgap light-emitting diode,” Opt. Express 15(11), 6727–6733 (2007). [CrossRef] [PubMed]

11.

J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102–1-201102–3 (2006).

12.

“M. El kurdi, S. David, P. Boucard, C. Kammerer, X. Li, V. Le Thanh, and S Sauvage, “Strong 1.3–1.5 μm luminescence from Ge/Si self-assembled islands in highly confining microcavities on silicon on insulator,” J. Appl. Phys. 96, 997–1000 (2004). [CrossRef]

13.

J. S. Xia, K. Nemoto, Y. Ikegami, and Y. Shiraki, “Silicon-based light emitters fabricated by embedding Ge self-assembled quantum dots in microdisks,” Appl. Phys. Lett. 91, 011104–1-011104–3 (2007). [CrossRef] [PubMed]

14.

M. El Kurdi, X. Checoury, S. David, T. P. Ngo, N. Zerounian, P. Boucaud, O. Kermarrec, Y. Campidelli, and D. Bensahel, “Quality factor of Si-based photonic crystal L3 nanocavities probed with an internal source,” Opt. Express 16(12), 8780–8791 (2008). [CrossRef] [PubMed]

15.

S. Fukatsu, N. Usami, T. Chinzei, Y. Shiraki, A. Nishida, and K. Nakagawa, “Electroluminescence from Strained SiGe/Si Quantum Well Structures Grown by Solid Source Si Molecular Beam Epitaxy,” Jpn. J. Appl. Phys. 31(Part 2, No. 8A), L1015–L1017 (1992). [CrossRef]

16.

T. Brunhes, P. Boucaud, S. Sauvage, F. Aniel, J.-M. Lourtioz, C. Hernandez, Y. Campidelli, O. Kermarrec, D. Bensahel, G. Faini, and I. Sagnes, “Electroluminescence of Ge/Si self-assembled quantum dots grown by chemical vapor deposition,” Appl. Phys. Lett. 77(12), 1822–1824 (2000). [CrossRef]

OCIS Codes
(230.3670) Optical devices : Light-emitting diodes
(140.3948) Lasers and laser optics : Microcavity devices
(130.3990) Integrated optics : Micro-optical devices

ToC Category:
Optical Devices

History
Original Manuscript: April 7, 2010
Revised Manuscript: May 31, 2010
Manuscript Accepted: June 2, 2010
Published: June 14, 2010

Citation
Jinsong Xia, Yuuki Takeda, Noritaka Usami, Takuya Maruizumi, and Yasuhiro Shiraki, "Room-temperature electroluminescence from Si microdisks with Ge quantum dots," Opt. Express 18, 13945-13950 (2010)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-18-13-13945


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References

  1. D. K. Nayak, N. Usami, S. Fukatsu, and Y. Shiraki, “Band-edge photoluminescence of SiGe/strained-Si/SiGe type-II quantum wells on Si(100),” Appl. Phys. Lett. 63(25), 3509–3511 (1993). [CrossRef]
  2. S. Fukatsu, N. Usami, Y. Kato, H. Sunamura, Y. Shiraki, H. Oku, T. Ohnishi, Y. Ohmori, and K. Okumura, “Gas-source molecular beam epitaxy and luminescence characterization of strained Si1-xGex/Si quantum wells,” J. Cryst. Growth 136(1-4), 315–321 (1994). [CrossRef]
  3. K. Kawaguchi, M. Morooka, K. Konishi, S. Koh, and Y. Shiraki, “Optical properties of strain-balanced SiGe planar microcavities with Ge dots on Si substrates,” Appl. Phys. Lett. 81(5), 817–819 (2002). [CrossRef]
  4. S. Fukatsu, H. Sunamuru, Y. Shiraki, and S. Komiyama, “Phononless radiative recombination of indirect excitons in a Si/Ge type-II quantum dot,” Appl. Phys. Lett. 71(2), 258–261 (1997). [CrossRef]
  5. L. Pavesi, L. Dal Negro, C. Mazzoleni, G. Franzò, and F. Priolo, “Optical gain in silicon nanocrystals,” Nature 408(6811), 440–444 (2000). [CrossRef]
  6. L. Dal Negro, M. Cazzanelli, L. Pavesi, S. Ossicini, D. Pacifici, G. Franzò, F. Priolo, and F. Iacona, “Dynamics of stimulated emission in silicon nanocrystals,” Appl. Phys. Lett. 82(26), 4636–4638 (2003). [CrossRef]
  7. G. Franzò, F. Priolo, S. Coffa, A. Polman, and A. Camera, “Room-temperature electroluminescence from Er‐doped crystalline Si,” Appl. Phys. Lett. 64(17), 2235–2237 (1994). [CrossRef]
  8. D. Pacifici, G. Franzò, F. Priolo, F. Iacona, and L. D. Negro, “Modeling and perspectives of the Si nanocrystals-Er interaction for optical amplification,” Phys.Rev.B 67, 245301–1-245301–13 (2003). [CrossRef]
  9. A. A. Shklyaev, Y. Nakamura, F. N. Dultsev, and M. Ichikawa, “Defect-related light emission in the 1.4-1.7μm range from Si layers at room temperature,” J. Appl. Phys. 105, 063513–1-063513–4 (2009).
  10. J. Bao, M. Tabbal, T. Kim, S. Charnvanichborikarn, J. S. Williams, M. J. Aziz, and F. Capasso, “Point defect engineered Si sub-bandgap light-emitting diode,” Opt. Express 15(11), 6727–6733 (2007). [CrossRef]
  11. J. S. Xia, Y. Ikegami, Y. Shiraki, N. Usami, and Y. Nakata, “Strong resonant luminescence from Ge quantum dots in photonic crystal microcavity at room temperature,” Appl. Phys. Lett. 89, 201102–1-201102–3 (2006).
  12. “M. El kurdi, S. David, P. Boucard, C. Kammerer, X. Li, V. Le Thanh, and S Sauvage, “Strong 1.3–1.5 μm luminescence from Ge/Si self-assembled islands in highly confining microcavities on silicon on insulator,” J. Appl. Phys. 96, 997–1000 (2004). [CrossRef]
  13. J. S. Xia, K. Nemoto, Y. Ikegami, and Y. Shiraki, “Silicon-based light emitters fabricated by embedding Ge self-assembled quantum dots in microdisks,” Appl. Phys. Lett. 91, 011104–1-011104–3 (2007).
  14. M. El Kurdi, X. Checoury, S. David, T. P. Ngo, N. Zerounian, P. Boucaud, O. Kermarrec, Y. Campidelli, and D. Bensahel, “Quality factor of Si-based photonic crystal L3 nanocavities probed with an internal source,” Opt. Express 16(12), 8780–8791 (2008). [CrossRef]
  15. S. Fukatsu, N. Usami, T. Chinzei, Y. Shiraki, A. Nishida, and K. Nakagawa, “Electroluminescence from Strained SiGe/Si Quantum Well Structures Grown by Solid Source Si Molecular Beam Epitaxy,” Jpn. J. Appl. Phys. 31(Part 2, No. 8A), L1015–L1017 (1992). [CrossRef]
  16. T. Brunhes, P. Boucaud, S. Sauvage, F. Aniel, J.-M. Lourtioz, C. Hernandez, Y. Campidelli, O. Kermarrec, D. Bensahel, G. Faini, and I. Sagnes, “Electroluminescence of Ge/Si self-assembled quantum dots grown by chemical vapor deposition,” Appl. Phys. Lett. 77(12), 1822–1824 (2000). [CrossRef]

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