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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 16, Iss. 7 — Mar. 31, 2008
  • pp: 4797–4803
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Photocurrent response from photonic crystal defect modes

Stephan Schartner, Michele Nobile, Werner Schrenk, Aaron Maxwell Andrews, Pavel Klang, and Gottfried Strasser  »View Author Affiliations


Optics Express, Vol. 16, Issue 7, pp. 4797-4803 (2008)
http://dx.doi.org/10.1364/OE.16.004797


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Abstract

The authors use a quantum well intersubband photodetector fabricated into a two dimensional photonic crystal to investigate the optical defect modes of a single missing hole defect. The modes appear as a local enhancement in spectral photocurrent due to an increased in-coupling of surface incident light when a defect mode is present. The frequencies of these localized modes are tracked as they are varied by the defect geometry and compared to simulations.

© 2008 Optical Society of America

1. Introduction

Photonic crystals (PhCs) [1

1. J. D. Joannopoulos, P. R. Villeneuve, and F. Shanhui, “Photonic Crystals,” Nature 386, 165–173 (1997).

] are playing an important role in the photonic device community. Especially two dimensional (2D) realizations found a huge field of applications in photonic circuits [2–4

2. Y. Tanaka, Y. Sugimoto, N. Ikeda, H. Nakamura, K. Kanamoto, K. Asakawa, and K. Inoue, “Design, fabrication, and characterization of a two-dimensional photonic-crystal symmetric Mach-Zehnder interferometer for optical integrated circuits,” Appl. Phys. Lett. 86, 141104 (2005). [CrossRef]

], fibers [5

5. P. Russell, “Photonic Crystal Fibers,” Science 299, 358–362 (2003). [CrossRef] [PubMed]

], and lasers [6–10

6. Painter, R. K. Lee, A. Scherer, A. Yariv, J. D. O’Brien, P. D. Dapkus, and I. Kim, “Two-Dimensional Photonic Band-Gap Defect-Mode Laser,” Science 284, 1819–1821 (1999). [CrossRef] [PubMed]

]. A substantial fraction of these implementations are based on the use of photonic defect modes. For intersubband based devices PhCs are of special interest since in- and out-coupling of light via the surface cannot directly be achieved in such devices due to their restriction to TM polarized light. Hence, there is always a need for a coupling scheme, which up to now has mainly been realized via shallow gratings for detection [11

11. J. Y. Andersson and L. Lundquist, “Near-unity quantum efficiency of AIGaAs/GaAs quantum well infrareddetectors using a waveguide with a doubly periodic grating coupler,” Appl. Phys. Lett. 59, 857–859 (1991). [CrossRef]

] as well as for emission [12

12. D. Hofstetter, J. Faist, M. Beck, and U. Oesterle, “Surface-emitting 10.1 µm quantum-cascade distributed feedback lasers,” Appl. Phys. Lett. 75, 3769–3771 (1999). [CrossRef]

,13

13. W. Schrenk, N. Finger, S. Gianordoli, L. Hvozdara, G. Strasser, and E. Gornik, “Surface-emitting distributed feedback quantum-cascade lasers,” Appl. Phys. Lett. 77, 2086–2088 (2000). [CrossRef]

]. Deep etched grating structures like a PhC quantum cascade laser [10

10. R. Colombelli, K. Srinivasan, M. Troccoli, O. Painter, C. Gmachl, D. M. Tennant, A. M. Sergent, D. I. Sivco, A. Y. Cho, and F. Capasso, “Quantum Cascade Surface-Emitting Photonic Crystal Laser,” Science 302, 1374–1377 (2003). [CrossRef] [PubMed]

] are under extensive investigation since they allow an increase in cavity design freedom, addressing surface emission, compactness of the device and beam shaping.

In a former publication [14

14. S. Schartner, S. Golka, C. Pflügl, W. Schrenk, A. M. Andrews, T. Roch, and G. Strasser, “Band structure mapping in photonic crystal intersubband detectors,” Appl. Phys. Lett. 89, 151107 (2006). [CrossRef]

] we demonstrated the possibility of a PhC characterization via intracavity mode detection by a GaAs/AlGaAs QWIP incorporated in a photonic crystal slab. The devices were illuminated under varying angles of incidence via their surface and whenever the in-plane wave vector end energy of an incoming wave matches a PhC mode, the light is coupled into the cavity. The TM polarized excited modes are absorbed by the QWIP and cause spectral enhancements in the photocurrent. Each PhC mode is therefore represented by a peak in the photocurrent spectrum, similar to the resonant features in the reflectivity measurements shown by Astratov et al. [15

15. V. N. Astratov, D. M. Whittaker, I. S. Culshaw, R. M. Stevenson, M. S. Skolnick, T. F. Krauss, and R. M. De-La-Rue, “Photonic band-structure effects in the reflectivity of periodically patterned waveguides,” Phys. Rev. B 60, R16255–R16258 (1999). [CrossRef]

] By tracing these peaks the band structure can be mapped including its polarization behavior. The agreement with theoretical calculations is excellent and it is therefore interesting whether this technique can be extended to the characterization of defect modes. We therefore introduced a single missing hole defect to a triangular PhC of air holes. Most applications use a triangular array of air holes since these structures provide viable band gaps for TE polarized light and are favorable over pillar structures that can not easily be electrically contacted. QWIPs rely on intersubband transitions and are therefore solely sensitive to radiation polarized perpendicular to the detecting region, hence TM polarized light. The TE band gaps and defect modes lying within can therefore not be utilized. Nevertheless the defect structure still gives rise to localized modes that may potentially be used.

2. Device description

2.1 Photonic crystal and defects

Fig. 1. SEM pictures of a finished and wire bonded device. The dotted parallelogram marks the unit cell of the 7×7 defect superlattice. This unit cell was also used for 2D simulations of the defect mode. The inset shows a close up of the defect structure including the relevant dimensions a, r and rD. The defect is build by a single missing hole with the six nearest neighboring holes being varied in diameter but not being displaced.

2.2 Waveguide

The vertical structure of the device is made up by a surface-plasmon [16

16. C. Sirtori, C. Gmachl, F. Capasso, J. Faist, D. I. Sivco, A. L. Hutchinson, and A. Y. Cho, “Longwavelength (λ≈8–11.5 µm) semiconductor lasers with waveguides based on surface plasmons,” Opt. Lett. 23, 1366–1368 (1998). [CrossRef]

] / plasmon enhanced [17

17. C. Sirtori, P. Kruck, S. Barbieri, H. Page, J. Nagle, M. Beck, J. Faist, and U. Oesterle, “Low-loss Al-free waveguides for unipolar semiconductor lasers,” Appl. Phys. Lett. 75, 3911–3913 (1999). [CrossRef]

] waveguide. The surface-plasmon cladding realized via the top contact allows a thin waveguide with a high confinement of the optical mode to the detecting region. This is however compromised by higher losses caused in the metal film. The reduced waveguide thickness eases the deep etching process significantly since the PhC holes need to penetrate the entire waveguide structure in order to keep its the guiding ability. The lower cladding is provided by a highly doped GaAs layer and the under laying highly doped substrate. The high doping level shifts the plasma frequency together with the according drop in refractive index into the mid-IR region.

3. Fabrication

3.1 Growth

The detecting region is formed by 50 periods of a standard GaAs/Al0.19Ga0.81As bound-to-quasibound QWIP [18

18. H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors, Vol. 126 (Springer, Berlin, 2007).

] and was grown by molecular beam epitaxy. The well and barrier widths are w=6.6 nm and b=54 nm respectively. The wells are delta doped to an equivalent sheet density of 3×1011 cm-2. Starting from the highly doped (2×1018 cm-3) substrate the layer sequence is as follows: 540 nm GaAs (2×1018 cm-3) acts as a lower cladding followed by an undoped 216 nm Al0.19Ga0.81As spacer layer and the detecting region (2.796 µm). Subsequently another 216 nm Al0.19Ga0.81As spacer layer (undoped) was grown before the contact facilitating layers: 108 nm GaAs (1×1018 cm-3) and 5 nm In0.53Ga0.47As (1×1019 cm-3). All layer thicknesses and Al contents were extracted from X-ray diffraction measurements after growth.

3.2 Device processing

The fabrication was carried out in a mix and match processing, where direct e-beam lithography was used to define the PhC pattern and standard UV contact lithography was done on top of that to define insulation openings as well as extended contact pads. As a first step Ge/Au/Ni/Au (15/30/14/60 nm) was evaporated, followed by a 300 nm SiNx layer. The e-beam written pattern is transferred via SF6 reactive ion etching (RIE) to the SiNx which - after removal of the PMMA - serves as a hard mask for Ar RIE of the top contact. In this way we circumvent a metal deposition after the deep etching step which could potentially short circuit the device. After the patterning of the metal contact the PhC was deep etched by SiCl4/N2 RIE [19

19. S. Golka, S. Schartner, W. Schrenk, and G. StrasserJ. Vac. Sci. Technol. B , “Low bias reactive ion etching of GaAs with a SiCl4/N2/O2 time-multiplexed process,” 25, 839–844 (2007). [CrossRef]

] where hole depths of ~5.5 µm were achieved. A SiNx insulation, Ti/Au contact pads and a Ge/Au/Ni/Au (15/30/14/60 nm) backside contact finish the processing. In addition to the PhC devices plain mesa structures (70×100 µm with a cleaved facet) with equal contacts were fabricated to optically and electrically characterize the QWIP.

4 Results and Discussion

4.1 Measurement setup

The chips were mounted in a liquid He flow cryostat fixed to a temperature of 10 K. The devices where biased and excited via a mid-IR broadband source. The unpatterned mesa samples where excited via their cleaved facet since a 45° wedge is not feasible due to the highly doped and therefore absorbing substrate. The PhC devices where illuminated at surface normal incidence or at specific angles of incidence and under different incoming polarizations. The angular resolution is ±5°, given by an 1 inch diaphragm and a 6 inch parabolic mirror used to focus the light on the sample. The photocurrent was spectrally resolved by a fourier transform infrared spectrometer in step-scan mode.

4.2 Band structure and defect mode mapping

Fig. 2. (a) A comparison of photocurrent spectra of the unpatterned reference sample (dashed line), a PhC device with (solid line) and without (chain dotted line) the defect. Two peaks at a/λ0=0.432 and 0.450 are caused by defect mode supported in-coupling. (b) Polarization dependent band structure mapping of a device without defect. Solid lines refer to calculated PhC modes of even symmetry, dotted lines refer to odd PhC modes. The experimental data points are marked as + for TM (π) incident and as - for TE (σ) incident light. Peaks that appear in either polarization are shown as open circles. (c) The same measurement for a device with defects (r/a=0.326 and rD/r=0.753).

4.3 Defect mode tuning

Fig. 3. The graph shows three photocurrent spectra taken for three different defect sizes rD/r. The modes experience a blue-shift with increasing defect size. The four resolved defect modes were attributed to simulated modes which are represented by their electric field pattern (large) and energy density (small).

Fig. 4. The dependence of measured defect mode frequencies (scatter plots) is compared to the simulation results. The broken lines mark the position of the flat band regions at the Γ-point. Solid lines represent the calculated energy shift of the four defect states shown in Fig. 3.

5. Summary

In conclusion we showed that with a QWIP processed to a 2D PhC slab and characterized under surface incident light the photonic band structure can be mapped out as well as the frequencies of localized defect modes can be determined. In our actual structure of a triangular PhCs - which does not employ a photonic band gap for the polarization used - we were able to detect four defect modes. They were attributed by their energy dependence over defect size which was compared to those of simulated modes.

Acknowledgements

The authors acknowledge the support by the EU-TRN Project POISE, the Austrian FWF project ADLIS, the “Gesellschaft für Mikro- und Nanoelektronik” GMe, and the PLATON project within the Austrian NANO Initiative.

References and links

1.

J. D. Joannopoulos, P. R. Villeneuve, and F. Shanhui, “Photonic Crystals,” Nature 386, 165–173 (1997).

2.

Y. Tanaka, Y. Sugimoto, N. Ikeda, H. Nakamura, K. Kanamoto, K. Asakawa, and K. Inoue, “Design, fabrication, and characterization of a two-dimensional photonic-crystal symmetric Mach-Zehnder interferometer for optical integrated circuits,” Appl. Phys. Lett. 86, 141104 (2005). [CrossRef]

3.

K. Busch, S. Lölkes, R. B. Wehrspohn, and H. Föll, Photonic Crystals (WILEY-VCH, Weinheim, 2004). [CrossRef]

4.

E. Viasnoff-Schwoob, C. Weisbuch, H. Benisty, C. Cuisin, E. Derouin, O. Drisse, G. H. Duan, L. Legouezigou, O. Zegouezigou, F. Pommereau, S. Golka, H. Heidrich, H. J. Hensel, and K. Janiak, “Compact wavelength monitoring by lateral outcoupling in wedged photonic crystal multimode waveguides,” Appl. Phys. Lett. 86, 101107 (2005). [CrossRef]

5.

P. Russell, “Photonic Crystal Fibers,” Science 299, 358–362 (2003). [CrossRef] [PubMed]

6.

Painter, R. K. Lee, A. Scherer, A. Yariv, J. D. O’Brien, P. D. Dapkus, and I. Kim, “Two-Dimensional Photonic Band-Gap Defect-Mode Laser,” Science 284, 1819–1821 (1999). [CrossRef] [PubMed]

7.

H. G. Park, S. H. Kim, S. H. Kwon, Y. G. Ju, J. K. Yang, J. H. Baek, S. B. Kim, and Y. H. Lee, “Electrically Driven Single-Cell Photonic Crystal Laser,” Science 305, 1444–1447 (2004). [CrossRef] [PubMed]

8.

T. D. Happ, M. Kamp, A. Forchel, J. L. Gentner, and L. Goldstein, “Two-dimensional photonic crystal coupled-defect laser diode,” Appl. Phys. Lett. 82, 4–6 (2003). [CrossRef]

9.

X. Wu, A. Yamilov, X. Liu, S. Li, V. P. Dravid, R. P. H. Chang, and H. Cao, “Ultraviolet photonic crystal laser,” Appl. Phys. Lett. 85, 3657–3659 (2004). [CrossRef]

10.

R. Colombelli, K. Srinivasan, M. Troccoli, O. Painter, C. Gmachl, D. M. Tennant, A. M. Sergent, D. I. Sivco, A. Y. Cho, and F. Capasso, “Quantum Cascade Surface-Emitting Photonic Crystal Laser,” Science 302, 1374–1377 (2003). [CrossRef] [PubMed]

11.

J. Y. Andersson and L. Lundquist, “Near-unity quantum efficiency of AIGaAs/GaAs quantum well infrareddetectors using a waveguide with a doubly periodic grating coupler,” Appl. Phys. Lett. 59, 857–859 (1991). [CrossRef]

12.

D. Hofstetter, J. Faist, M. Beck, and U. Oesterle, “Surface-emitting 10.1 µm quantum-cascade distributed feedback lasers,” Appl. Phys. Lett. 75, 3769–3771 (1999). [CrossRef]

13.

W. Schrenk, N. Finger, S. Gianordoli, L. Hvozdara, G. Strasser, and E. Gornik, “Surface-emitting distributed feedback quantum-cascade lasers,” Appl. Phys. Lett. 77, 2086–2088 (2000). [CrossRef]

14.

S. Schartner, S. Golka, C. Pflügl, W. Schrenk, A. M. Andrews, T. Roch, and G. Strasser, “Band structure mapping in photonic crystal intersubband detectors,” Appl. Phys. Lett. 89, 151107 (2006). [CrossRef]

15.

V. N. Astratov, D. M. Whittaker, I. S. Culshaw, R. M. Stevenson, M. S. Skolnick, T. F. Krauss, and R. M. De-La-Rue, “Photonic band-structure effects in the reflectivity of periodically patterned waveguides,” Phys. Rev. B 60, R16255–R16258 (1999). [CrossRef]

16.

C. Sirtori, C. Gmachl, F. Capasso, J. Faist, D. I. Sivco, A. L. Hutchinson, and A. Y. Cho, “Longwavelength (λ≈8–11.5 µm) semiconductor lasers with waveguides based on surface plasmons,” Opt. Lett. 23, 1366–1368 (1998). [CrossRef]

17.

C. Sirtori, P. Kruck, S. Barbieri, H. Page, J. Nagle, M. Beck, J. Faist, and U. Oesterle, “Low-loss Al-free waveguides for unipolar semiconductor lasers,” Appl. Phys. Lett. 75, 3911–3913 (1999). [CrossRef]

18.

H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors, Vol. 126 (Springer, Berlin, 2007).

19.

S. Golka, S. Schartner, W. Schrenk, and G. StrasserJ. Vac. Sci. Technol. B , “Low bias reactive ion etching of GaAs with a SiCl4/N2/O2 time-multiplexed process,” 25, 839–844 (2007). [CrossRef]

20.

K. Sakoda, Optical Properties of Photonic Crystals, Vol. 80 (Springer, Berlin, 2001).

21.

S. G. Johnson and J. D. Joannopoulos, “Block-iterative frequency-domain methods for Maxwell’s equations in a planewave basis,” Opt. Express 8, 173–190 (2001). [CrossRef] [PubMed]

OCIS Codes
(040.4200) Detectors : Multiple quantum well
(230.5160) Optical devices : Photodetectors
(240.6680) Optics at surfaces : Surface plasmons
(050.5298) Diffraction and gratings : Photonic crystals
(250.0040) Optoelectronics : Detectors

ToC Category:
Detectors

History
Original Manuscript: December 17, 2007
Revised Manuscript: February 4, 2008
Manuscript Accepted: February 4, 2008
Published: March 24, 2008

Citation
Stephan Schartner, Michele Nobile, Werner Schrenk, Aaron M. Andrews, Pavel Klang, and Gottfried Strasser, "Photocurrent response from photonic crystal defect modes," Opt. Express 16, 4797-4803 (2008)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-16-7-4797


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References

  1. J. D. Joannopoulos, P. R. Villeneuve, and F. Shanhui, "Photonic Crystals," Nature 386, 165-173 (1997).
  2. Y. Tanaka, Y. Sugimoto, N. Ikeda, H. Nakamura, K. Kanamoto, K. Asakawa, and K. Inoue, "Design, fabrication, and characterization of a two-dimensional photonic-crystal symmetric Mach-Zehnder interferometer for optical integrated circuits," Appl. Phys. Lett. 86, 141104 (2005). [CrossRef]
  3. K. Busch, S. Lölkes, R. B. Wehrspohn, and H. Föll, Photonic Crystals (WILEY-VCH, Weinheim, 2004). [CrossRef]
  4. E. Viasnoff-Schwoob, C. Weisbuch, H. Benisty, C. Cuisin, E. Derouin, O. Drisse, G. H. Duan, L. Legouezigou, O. Zegouezigou, F. Pommereau, S. Golka, H. Heidrich, H. J. Hensel, and K. Janiak, "Compact wavelength monitoring by lateral outcoupling in wedged photonic crystal multimode waveguides," Appl. Phys. Lett. 86, 101107 (2005). [CrossRef]
  5. P. Russell, "Photonic Crystal Fibers," Science 299, 358-362 (2003). [CrossRef] [PubMed]
  6. Painter, R. K. Lee, A. Scherer, A. Yariv, J. D. O'Brien, P. D. Dapkus, and I. Kim, "Two-Dimensional Photonic Band-Gap Defect-Mode Laser," Science 284, 1819-1821 (1999). [CrossRef] [PubMed]
  7. H. G. Park, S. H. Kim, S. H. Kwon, Y. G. Ju, J. K. Yang, J. H. Baek, S. B. Kim, and Y. H. Lee, "Electrically Driven Single-Cell Photonic Crystal Laser," Science 305, 1444-1447 (2004). [CrossRef] [PubMed]
  8. T. D. Happ, M. Kamp, A. Forchel, J. L. Gentner, and L. Goldstein, "Two-dimensional photonic crystal coupled-defect laser diode," Appl. Phys. Lett. 82, 4-6 (2003). [CrossRef]
  9. X. Wu, A. Yamilov, X. Liu, S. Li, V. P. Dravid, R. P. H. Chang, and H. Cao, "Ultraviolet photonic crystal laser," Appl. Phys. Lett. 85, 3657-3659 (2004). [CrossRef]
  10. R. Colombelli, K. Srinivasan, M. Troccoli, O. Painter, C. Gmachl, D. M. Tennant, A. M. Sergent, D. I. Sivco, A. Y. Cho, and F. Capasso, "Quantum Cascade Surface-Emitting Photonic Crystal Laser," Science 302, 1374-1377 (2003). [CrossRef] [PubMed]
  11. J. Y. Andersson and L. Lundquist, "Near-unity quantum efficiency of AIGaAs/GaAs quantum well infrareddetectors using a waveguide with a doubly periodic grating coupler," Appl. Phys. Lett. 59, 857-859 (1991). [CrossRef]
  12. D. Hofstetter, J. Faist, M. Beck, and U. Oesterle, "Surface-emitting 10.1 µm quantum-cascade distributed feedback lasers," Appl. Phys. Lett. 75, 3769-3771 (1999). [CrossRef]
  13. W. Schrenk, N. Finger, S. Gianordoli, L. Hvozdara, G. Strasser, and E. Gornik, "Surface-emitting distributed feedback quantum-cascade lasers," Appl. Phys. Lett. 77, 2086-2088 (2000). [CrossRef]
  14. S. Schartner, S. Golka, C. Pflügl, W. Schrenk, A. M. Andrews, T. Roch, and G. Strasser, "Band structure mapping in photonic crystal intersubband detectors," Appl. Phys. Lett. 89, 151107 (2006). [CrossRef]
  15. V. N. Astratov, D. M. Whittaker, I. S. Culshaw, R. M. Stevenson, M. S. Skolnick, T. F. Krauss, and R. M. De-La-Rue, "Photonic band-structure effects in the reflectivity of periodically patterned waveguides," Phys. Rev. B 60, R16255-R16258 (1999). [CrossRef]
  16. C. Sirtori, C. Gmachl, F. Capasso, J. Faist, D. I. Sivco, A. L. Hutchinson, and A. Y. Cho, "Long-wavelength (λ ≈ 8-11.5 µm) semiconductor lasers with waveguides based on surface plasmons," Opt. Lett. 23, 1366-1368 (1998). [CrossRef]
  17. C. Sirtori, P. Kruck, S. Barbieri, H. Page, J. Nagle, M. Beck, J. Faist, and U. Oesterle, "Low-loss Al-free waveguides for unipolar semiconductor lasers," Appl. Phys. Lett. 75, 3911-3913 (1999). [CrossRef]
  18. H. Schneider and H. C. Liu, Quantum Well Infrared Photodetectors, Vol. 126 (Springer, Berlin, 2007).
  19. S. Golka, S. Schartner, W. Schrenk, and G. Strasser, "Low bias reactive ion etching of GaAs with a SiCl4/N2/O2 time-multiplexed process," J. Vac. Sci. Technol. B 25, 839-844 (2007). [CrossRef]
  20. K. Sakoda, Optical Properties of Photonic Crystals, Vol. 80 (Springer, Berlin, 2001).
  21. S. G. Johnson and J. D. Joannopoulos, "Block-iterative frequency-domain methods for Maxwell's equations in a planewave basis," Opt. Express 8, 173-190 (2001) [CrossRef] [PubMed]

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