Spectral data for a ZnSe film grown on GaAs(100) are obtained at room
temperature by spectroscopic ellipsometry (SE) in the photon energy ra
nge between 1.5 eV and 6 eV in steps of 5 meV. The optical dielectric
function for bulk ZnSe is successfully extracted from the spectral dat
a utilizing a multilayer analysis. The resultant data are better than
previous data in that (1) the real part of the dielectric function bel
ow the band gap decreases smoothly following closely Marple's data obt
ained by the beam deviation method, which is more reliable than SE in
this energy range, (2) the data reveal four distinctive critical point
structures at E(0), E(0) + Delta(0), E(1), and E(1) + Delta(1), as is
expected from the band structure, and (3) the maximum value of the im
aginary part of the dielectric function in the E(1) region is highest
among the reported data. The resultant data are expressed as a functio
n of critical-point parameters and photon energies using our model, wh
ich is more generally valid than other models. This enables us to calc
ulate the optical dielectric function not only over the entire photon
energy range of the given spectral data, but also below and somewhat a
bove the given spectral range. The excitonic effects apparently presen
t in the spectral data are incorporated in our model. This enables us
to determine excitonic parameters. The excitonic binding energy at Eo
is found to be 13 meV at room temperature.