Ellipsometric study of silicon nanocrystal optical constants

Samples of silicon nanocrystals on various substrates were prepared by cluster beam deposition of silicon nanoparticles, obtained by laser-induced pyrolysis of silane in a flow reactor. Using optical ellipsometry, the optical properties (refractive index and extinction coefficient) of the as-prepared silicon nanocrystal layers were determined in the wavelength range from 240 to 700 nm. Two dispersion models were used to describe the silicon nanocrystal optical properties: the Bruggeman effective medium approximation model and the Tauc-Lorentz model. The study showed that while a simple Bruggeman effective medium approximation model could not completely account for the silicon nanocrystal dispersion behavior, the optical response of the silicon nanocrystal layers could be satisfactorily described by a Tauc-Lorentz model. The present study also showed that, as for porous silicon, the silicon nanocrystal optical indexes significantly deviate from those of bulk crystalline and amorphous silicon. It confirms the special behavior of silicon under its nanoscale form. (C) 2003 American Institute of Physics.