Numerical Derivative Analysis of the Pseudodielectric Functions of ZnTe

The real (ε 1 ) and imaginary (ε 2 ) parts of the dielectric function of ZnTe have been measured by spectroscopic ellipsometry in the 1.5-5.6-eV photon-energy range at room temperature. The measured spectra reveal distinct structures at energies of the E 0 , E 1 , E 1 +Δ 1 , and E 2 critical points (CPs). These data are analyzed by fitting the first-(dε/d E ) or second-derivative spectrum (d 2 ε/d E 2 ) with model dielectric functions (MDF) or standard critical-point line shapes (SCP). It is found that both the MDF and SCP models successfully explain the measured derivative spectra. The MDF also shows excellent agreement with the experimental ε(ω) spectra, but the SCP does not. The CP energies determined here are: E 0 =2.28 eV; E 1 =3.78 eV; E 1 +Δ 1 =4.34 eV; and E 2 =5.23 eV. The E 1 - and ( E 1 +Δ 1 )-exciton binding energies for ZnTe are also estimated to be ∼0.19 eV.