Dresden 2009 – scientific programme
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MM: Fachverband Metall- und Materialphysik
MM 28: Electronic Properties I
MM 28.3: Talk
Wednesday, March 25, 2009, 10:45–11:00, IFW D
Phonon absorption at low temperature - determination of the indirect band gap in FeSi using Fourier-spectroscopic infrared ellipsometry — •Dirk Menzel1, Paul Popovich2, Alexander V. Boris2, and Joachim Schoenes1 — 1Institut für Physik der Kondensierten Materie, TU Braunschweig, Germany — 2Max-Planck-Institut für Festkörperforschung, Stuttgart, Germany
The determination of the band gap is an important parameter for the characteristics of a semiconductor. However, for FeSi the size of the gap is not reported consistently so far. Using far-infrared spectroscopic ellipsometry we have reliably determined the dielectric function of FeSi. As predicted by band structure calculations both a direct and an indirect band gap are observed from the absorptive part of the dielectric function which amount to 73 meV and 10 meV, respectively. The absolute value of the indirect gap can only be evaluated when both phonon absorption and emission are observed. At low temperature, however, the former does not occur which generally makes it impossible to obtain the indirect gap energy in the low temperature range. For the ellipsometric measurements we used a Fourier transform spectrometer and, therefore, illuminated the sample with white light. This leads to a continuous generation of optical phonons which may also decay into low-energy acoustic phonons. This method enables one to derive the absolute value of the indirect gap even the low temperature.