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

Abstract

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 $0.6<\ensuremath{\hbar}\ensuremath{\omega}<30$ eV at temperatures $90<T<400$ K. The reflectance was analyzed via the Kramers---Kronig relations. We report curves for ${\ensuremath{\epsilon}}_{1}$, ${\ensuremath{\epsilon}}_{2}$, $\ensuremath{-}\mathrm{Im}(\frac{1}{\ensuremath{\epsilon}})$, and ${N}_{\mathrm{eff}}(\ensuremath{\hbar}\ensuremath{\omega})$ for all of the $\mathrm{II}B\ensuremath{-}\mathrm{V}\mathrm{I}$ 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.