Infrared absorption of small silicon particles with oxide overlayers

The infrared optical absorption coefficient for spherical particles coated with a dielectric mantel and imbedded in a nonabsorbing dielectric medium has been predicted based on calculations of the average dielectric function. The theory represents an extension of the continuum, volume-averaging model of Genzel and Martin. The average dielectric function is calculated, and the consequences are considered for the case of Si-SiO2 dispersed in CsI. The average absorption coefficient is displayed for intrinsic and doped Si spheres with a range of oxide mantel thicknesses. The absorption spectra are seen to be dominated by the absorption of the SiO2, even for very thin layers. Structure is predicted in the average absorption coefficient between 1100 and 1300 cm−1 which has no counterpart in either SiO2 or Si (with or without free carriers). The structures, though different in origin, are reminiscent of the “antiresonance” and nearby high frequency strong absorption previously found only for surface plasmon-surface phonon interactions in small spheres.