Weinberg 2
06120 Halle
Germany
Tel: 0345-5582-654 (A. Ebensing)
Fax: 0345-5582-557
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
Institut für Physik, Humboldt-Universität zu Berlin
Hausvogteiplatz 5-7
10117 Berlin
Germany
Phone: ++49-30-2093 4711 (office)
Fax: ++49-30-2093 4718
Phone: ++49-30-2093 4711 (office)
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 (MPI Halle) 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:
A. Birner, A.-P. Li , F. Müller, U. Gösele, P. Kramper, V. Sandoghdar, J. Mlynek, K. Busch, and V. Lehmann: Transmission of a microcavity structure in a two-dimensional photonic crystal based on macroporous silicon; Mater. Sci. Semicon. Proces. 3 (2000) 487-491.
J. Schilling, F. Müller, S. Matthias, R.B. Wehrspohn, U. Gösele, and K. Busch: 3D photonic crystals made out of macroporous silicon by modulation of pore diameter; Appl. Phys. Lett. 78 (2001) 1180-1182.
J. Schilling et al.: A model system for two-dimensional and three-dimensional photonic crystals: macroporous silicon; Journal of Optics A: Pure and Appl. Opt. 3 (2001) 121-132.
J. Schilling, A. Birner, F. Müller, R.B. Wehrspohn, R. Hillebrand, U. Gösele, K. Busch, S. John, S.W. Leonard, and H.M. vam Driel: Optical characterisation of 2D macroporous silicon photonic crystals with bandgaps around 3.5 and 1.3µm; Opt. Mat. 17 (2001) 7-10.
P. Kramper, A. Birner, M. Agio, C.M. Soukoulis, F. Müller, U. Gösele, J. Mlynek, and V. Sandoghdar: Direct spectroscopy of a deep two-dimensional photonic crystal microresonator; Phys. Rev. B 64 (2001) 233102.
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