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Optical Investigation of the Small Polaron in β‐FeSi 2
Author(s) -
Birkholz U.,
Naegele J.
Publication year - 1970
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19700390121
Subject(s) - polaron , materials science , condensed matter physics , free carrier absorption , phonon , absorption (acoustics) , reflectivity , optical conductivity , band gap , doping , drude model , free carrier , wavelength , conductivity , phase (matter) , thermal conduction , electronic band structure , optics , optoelectronics , chemistry , physics , electron , organic chemistry , quantum mechanics , composite material
The reflectivity of α‐FeSi 2 and also of β‐FeSi 2 doped with Co (n‐type) or Al (p‐type) has been investigated for wavelengths between 1 and 25 μm. The results for α‐FeSi 2 indicate metallic conduction in this material. The reflectivity of the undoped semiconducting phase β‐FeSi 2 can be explained by a fundamental absorption corresponding to a band gap E g = 0.8 eV and a reststrahlen band. The highest branch of the longitudinal optical phonons is found at 20.6 μm. The reflectivity of p‐FeSi 2 can be interpreted using Drude's theory of free carrier absorption. The optical properties of n‐FeSi 2 cannot be explained by free carrier absorption. A consistent interpretation, however, is possible in terms of the small polaron picture. Using the experimental data of the de conductivity and its activation energy the reflectivity of n‐FeSi 2 can be calculated. There is good agreement with the observed values. These results confirm an analysis of the transport properties of β‐FeSi 2 which was presented in a previous paper.