Far-Ultraviolet Reflectance of II-VI Compounds and Correlation with the Penn—Phillips Gap

Synchrotron radiation and standard light sources have been used to measure the polarization-dependent reflectance spectra of BeO, ZnO, ZnS, ZnSe, ZnTe, MgO, CdO, CdS, CdSe, and CdTe for photon energies 0.6<ω<30 eV at temperatures $90<T<400$ K. The reflectance was analyzed via the Kramers---Kronig relations. We report curves for ε₁, ε₂, -Im(1ε), and Neff(ω) for all of the IIB-VI compounds studied. Strong structures in the valence-band transition region of the zinc compounds and of the cadmium compounds were found to scale linearly with the Penn---Phillips average energy gap. Reflectance structures corresponding to core excitations were observed. A doublet at about 13.5 eV in CdS, CdSe, and CdTe was identified as a spin-orbit-split transition from the Cd $4d$ level. The observed spin-orbit splitting of this level was 0.6 eV. A shoulder on the low-energy side of this doublet in CdTe at 12.8 eV is identified as originating in the Te $5s$ band.