Berlin 2005 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 58: Poster IIb

HL 58.39: Poster

Dienstag, 8. März 2005, 16:30–19:00, Poster TU F

Tuning of the defect mode in a three dimensional photonic crystal made of macroporous silicon and a liquid crystal — •Guido Mertens¹, Sven Matthias², Ralf Wehrspohn¹, and Heinz Kitzerow¹ — ¹Faculty of Science, University of Paderborn, Warburger Str. 100, 33098 Paderborn — ²Max Planck Institute of Microstructure Physics, Weinberg 2, 06120 Halle

Variations of the refractive index can be utilized in order to shift the stop band in photonic crystals. We report on investigations of three-dimensional macroporous silicon structures which are filled with a liquid crystal. The sample contains a two-dimensional array of pores with periodically varying diameter. A plane with constant pore diameter embedded between two three-dimensional structures with varying pore diameter forms a micro resonator. FTIR measurements indicate a defect mode that can be shifted by changing the temperature. In transmission, a peak at the wavelength 7.184 micrometers appears in the centre of the second stopband, which can be attributed to a localised defect mode. Filling the structure with the liquid crystal 5CB (Merck) causes a red-shift of the stopband. Together with the stopband, the wavelength of the defect state is shifted by 191 nm to the larger wavelength 7.375 micrometers at 24 centigrades. An additional shift by 20 nm to a wavelength of 7.395 micrometers is caused when the liquid crystal is heated from the nematic phase (24 centigrades) to the isotropic phase (40 centigrades). These results are in qualitative agreement with theoretical calculations based on a transfer matrix model.