Nanotechnikum
Heinrich-Damerow-Str. 4
06120 Halle
Germany
fon (direct) : (+49) 345 5589 100
fon (secr.) : (+49) 345 28 517
fax : (+49) 345 27 391
Laboratory of Physical Chemistry, Eidgenössische Technische Hochschule (ETH) Zürich, CH
HCI F 205
ETH Hönggerberg
CH-8093 Zürich
Schweiz
Tel: +41 1 633 46 21
Fax: +41 1 633 1316
We propose a series of experiments on the fabrication, characterization and usage of photonic crystals made of macroporous silicon. Our fabrication approach is based on our know-how and experience in electrochemical etching of deep two dimensional crystals that have shown band gaps in the wavelength regimes down to 3µm. In the proposed research we intend to scale these structures to wavelength domains of 1.3µm and 1.5µm.
Macroporous silicon develops if silicon is electrochemically etched in hydrofluoric acid (HF). Using lithographic prestructuring the nucleation spots of the pores can be defined at the surface of a (100)-oriented n-type silicon wafer. This allows to determine a periodic pore pattern and to control the lattice constant of this pore lattice over a large range between 8µm and 0.5µm.
The etching process is performed under anodic bias with photogenerated holes. The pore walls are protected against electrochemical dissolution by a space charge region originating from the silicon/electrolyte contact. This process results in a periodic array of straight air pores in silicon with very high aspect ratios of 100-500. The porosity of the photonic crystals can be adjusted by the etch control parameters, i.e. the composition of the electrolyte, the light flux, and the anodic potential. This leads to a specific pore width and hereby to the r/a-ratio (radius to lattice constant), which determines the bandgap edges.
Such a structure represents an ideal 2D photonic crystal exhibiting novel properties for the propagation of infrared light inside. It has a complete 2D bandgap for infrared light travelling perpendicular to the pore axis. Because of the lithographic prestructuring technique defects can be intentionally incorporated into the photonic crystal. Omitting a single pore or a whole line of pores creates microresonators or photonic crystal waveguides.
Fig. 1 a) A top view of a zoom into the region of the crystal containing the microresonator. b) An overview of the photonic crystal substrate.
Fig. 2 a) Schematics of the setup for the optical measurements. The laser beam (LB) is focused onto the first waveguide at the entrance facet of the photonic crystal (PC). The transmitted light is collected locally with an uncoated optical fiber tip (FT) at the exit of the second wave guide. RD, 3DTS, 3DPS, TF, and D stand for reference detector, three-dimensional translation stage, three-dimensional piezo scanner, quartz tuning fork and detector, respectively. b) A typical raster-scanned image obtained at the output facet of the crystal in the xy plane, represented by a linear color scale.
Current project:
We also plan to fabricate novel 3D and index-guided 2D photonic crystals with implemented arbitrary defect structures. This allows the realization of optical devices and functionalities such as waveguides, microresonators, beam splitters, interferometers, etc. that are ideally suited for integrated optics. Optical properties of the fabricated photonic crystals will be studied extensively using a variety of techniques. In addition to transmission and reflection spectroscopy, we plan to apply local measurements and manipulations using methods of scanning probe microscopy. Near-field optical imaging (SNOM) will allow us to directly map the intensity and field distributions of light within subwavelength geometries such as a single defect mode of a photonic crystal, thereby visualizing confinement and propagation of light in smallest structures.
Furthermore, we plan to couple nanoscopic active media containing Er3+ ions and semiconductor quantum dots to a photonic crystal in order to study the modification of their radiation properties.
Projectleaders: R.B. Wehrspohn (UNI Paderborn) V. Sandoghdar (ETH Zürich) and O. Benson (HU Berlin)
Team: W. Trabesinger and P. Olk (ETH Zürich), J. Schilling, S. Matthias, and S. Schweizer (MPI Halle)
Cooperation: M. Zacharias (MPI-Halle), A.Rogach (Uni Hamburg), K. Busch (Uni Karlsruhe).
Funding: DFG in the framework of the Schwerpunktprogramm "Photonische Kristalle" under WE 2637/3-2 and SA 827/1-2
Recent publications:
Recent publications (Updated 21.10.2004):
1. P. Kramper, M. Agio, C.M. Soukoulis, A. Birner, F. Müller, R.B. Wehrspohn, U. Gösele, V. Sandoghdar, Highly Directional Emission from Photonic Crystal Waveguides of Subwavelength Width. Physical Review Letters, 2004. 92(11): p. 113903-1 - 113903-4
2. P. Kramper, M. Kafesaki, C. Soukoulis, A. Birner, F. Müller, U. Gösele, R.B. Wehrspohn, J. Mlynek, V. Sandoghdar, Near-field visualization of light confinement in a photonic crystal microresonator. Optics Letters, 2004. 29(2): p. 174-176
3. P. Olk, B. C. Buchler, V. Sandoghdar, N. Gaponik, A. Eychüller, A. L. Rogach, Subwavelength emitters in the near-infrared based on mercury telluride nanocrystals, Appl. Phys. Lett. 84, 4732 (2004).
4. S. Richter, S.L. Schweizer, R. Hillebrand, C. Jamois, R.B. Wehrspohn, M. Zacharias. U. Gösele, Periodically Arranged Point Defects in a Two Dimensional Photonic Crystal- The Photonic Analogue to a Doped Semiconductor. Proc. of SPIE, 2004. 5277: p. 238-243
5. S. Richter, S.L. Schweizer, R. Hillebrand, C. Jamois, R.B. Wehrspohn, M. Zacharias. U. Gösele, Interaction of Periodically Arranced Point Defects in a Two Dimensional Photonic Crystal - The Photonic Analogue to a Doped Semiconductor. Mat. Res. Soc. Symp. Proc., 2004. 797: p. W3.2.1-W3.2.6
6. S. Richter, R. Hillebrand, C. Jamois, M. Zacharias, U. Gösele, S.L. Schweizer and R.B. Wehrspohn, Peridodically Arranged point defect in two-dimensional photonic crystals, Phys. Rev. B, accepted 2004.
7. S. Matthias, F. Müller, R.B. Wehrspohn, U. Gösele, Large-scale fabrication of three-dimensional silicon photonic crystals with complete photonic bandgap, Adv. Mater. (2004), in print.
8. B. C. Buchler, P. Kramper, M. Kafesaki, C. M. Soukoulis, V. Sandoghdar, Near-field optical investigations of photonic crystal microresonators, IEICE Trans. Electron. E87-C, 371 (2004).
9. L. Rogobete, H. Schniepp, V. Sandoghdar, C. Henkel, "Spontaneous emission in nanoscopic dielectric particles", Opt. Lett. 28, 1736 (2003).
10. H.W. Tan, H.M. van Driel, S.L. Schweizer, R.B. Wehrspohn, and U. Gösele, Tuning a 2D silicon photonic crystals using non-linear optics, Phys. Rev. B (2004), in print.
11. L. Rogobete and C. Henkel “Spontaneous emission in a subwavelength environment characterized by boundary integral equations” to appear in Phys. Rev. A. (2004).
12. S. Richter, M. Steinhart, H. Hofmeister, M. Zacharias, U. Gösele, S.L. Schweizer, A. v. Rhein, R.B. Wehrspohn, N. Gaponik, A. Eychmüller, A. Rogach, “Quantum Dot Emitters in Two-Dimensional Photonic Crystals of Macroporous Silicon, Appl. Phys. Lett., submitted.
13. F. Koenderink, M. Kafesaki, B. Buchler, V. Sandoghdar ”Tuning a photonic crystal microresonator with a subwavelength near-field probe”, Phys. Rev. B. (submitted Sept. 2004).
As well as review articles from the last two years:
14. T. Geppert, J. Schilling, R.B. Wehrspohn, U. Gösele, Silicon-based photonic crystals. Top. Appl. Phys. 2004: 94 p. 295-322
15. R.B. Wehrspohn, J. Schilling, J. Choi, Y. Luo, S. Matthias, S.L. Schweizer, F. Müller, U. Gösele, S. Lölkes, S. Langa, J. Carstensen, H. Föll, Electrochemically-prepared 2D and 3D photonic crystals. In Photonic Crystals - Advances in Design, Fabrication, and Characterization, (Wiley-VCH) 2004. : p. 63-82
16. V. Sandoghdar, B. Buchler, P. Kramper, S. Götzinger, O. Benson, M. Kafesaki, Scanning near-field optical studies of photonic devices, in Photonic crystals-Advances in Design, Fabrication, and Characterization, Wiley-VCH, Weinheim, Germany (2004) p. 215-237.
17. R.B. Wehrspohn, J. Schilling, A model system for photonic crystals: macroporous silicon. Phys. Stat. Sol a, 2003. 197(3): p. 673-687
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