Birefringence and Anisotropic Optical Absorption
in Porous Silicon

A. I. Efimova*, E. Yu. Krutkova, L. A. Golovan’, M. A. Fomenko,
P. K. Kashkarov, and V. Yu. Timoshenko

Department of Physics, Moscow State University, Moscow, 119992 Russia

*e-mail: efimova@vega.phys.msu.ru

Received February 8, 2007

Abstract—The refractive indices and the coefficients of optical absorption by free charge carriers and local
vibrations in porous silicon (por-Si) films, comprising nanometer-sized silicon residues (nanocrystals) sepa-
rated by nanometer-sized pores (nanopores) formed in the course of electrochemical etching of the initial single
crystal silicon, have been studied by polarization-resolved IR absorption spectroscopy techniques. It is shown
that the birefringence observed in por-Si is related to the anisotropic shapes of nanocrystals and nanopores,
while the anisotropy (dichroism) of absorption by the local vibrational modes is determined predominantly by
the microrelief of the surface of nanocrystals. It is demonstrated that silicon–hydrogen surface bonds in nanoc-
rystals can be restored by means of selective hydrogen thermodesorption with the formation of a considerable
number of H-terminated surface Si–Si dimers.

PACS numbers: 78.20.Ci, 78.20.Fm

DOI: 10.1134/S1063776107090178

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