NUMERICAL DERIVATIVE ANALYSIS OF THE PSEUDODIELECTRIC FUNCTION OF CDTE

The real (epsilon1) and imaginary (epsilon2) parts of the dielectric function for CdTe have been measured by spectroscopic ellipsometry in the 1.1-5.6-eV photon-energy range at room temperature. The measured spectra reveal distinct structures at energies of the E0, E0+DELTA0, E1, E1+DELTA1 and E2 oritical points (CPs). These data are analyzed by fitting the first-(depsilon/dE) or second-derivative spectra (d2epsilon/dE2) with model dielectric functions (MDF) or standard critical-point (SCP) line shapes. 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 epsilon(omega) spectra, but the SCP does not. The CP energies determined here are: E0=1.58 eV; E0+DELTA0=2.55 eV; E1=3.55 eV; E1+DELTA1=4.13 eV; and E2=5.13 eV.