OBSERVATION OF CO2-XCOXSE THIN-FILMS BY SPECTROSCOPIC ELLIPSOMETRY( INTRAION TRANSITIONS IN ZN1)

We report the first ellipsometric observation of an optical transition associated with the crystal field levels in the localized d-states. I n the ellipsometric spectra of Zn1-xCoxSe films with 0.04 less than or equal to x<0.1 grown on GaAs substrates, sharp distortions of the int erference patterns below the fundamental band gap were observed at ene rgies between 1.6 similar to 1.9 eV. To understand this, we calculated multilayer model (air/Zn1-xCoxSe/GaAs). The dielectric function of th e film is approximated by using harmonic oscillator model with two osc illators with transition energies at 1.67 and 1.83 eV. The calculated pseudodielectric function shows the same behavior as our measured pseu dodielectric response, resulting that our da:a shows the clear existen ce of the absorptions due to intra d to d transitions of Co2+ ions und er a tetrahedral crystal field.