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HL: Fachverband Halbleiterphysik
HL 19: Silicon and Germanium
HL 19.13: Vortrag
Montag, 14. März 2011, 17:45–18:00, POT 251
Determination of the complex refractive index in the infrared region for femtosecond-laser-formed silicon surfaces using ray-tracing — •Augustinas Ruibys1, Christian Lehmann2, Thomas Gimpel3, Anna Lena Baumann1, Stefan Kontermann1, and Wolfgang Schade1,3 — 1Fraunhofer Heinrich Hertz Institute, Energie-Campus, Am Stollen 19, 38640 Goslar — 2FU Berlin, Fachbereich für Experimentalphysik, Arnimallee 14, 14195 Berlin — 3Clausthal University of Technology, EFZN, Energie-Campus, Am Stollen 19, 38640 Goslar
The femtosecond-laser processing of silicon surface in the SF6 gas creates cone-shaped structures, which have a thin 0.1 - 1 μm layer of multi-crystalline substance with approximately 0.5 at.% of sulphur. This layer is known to be photovoltaically active in the visible wavelengths as well as in the infrared and has the potential for cost effective solar cells. However, not much is known about the fundamental properties of this multi-crystalline layer. Measuring the optical properties in the infrared and simulating ray-traces in the coned surface, allows calculating the complex refractive index and the associated absorption coefficient. The simulated refractive index spectra are presented for samples processed in SF6 gas and vacuum in the wavelength range 1100 nm - 2500 nm. The obtained absorption coefficient spectra for samples processed in SF6 are of the order of 10^4 cm-1. This high absorption in the infrared is discussed from the point of view of the introduced sub-band-gap energy levels on the one hand and high free carrier absorption on the other hand.