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 $0.6<\mathrm{}\hslash \omega <30\mathrm{}$ eV at temperatures $90<T<\mathrm{}400\mathrm{}$ K. The reflectance was analyzed via the Kramers—Kronig relations. We report curves for ${\epsilon }_1$, ${\epsilon }_2$, $-\mathrm{Im}\left(\frac{1}{\epsilon }\right)$, and $N_{\mathrm{eff}}\left(\hslash \omega \right)$ for all of the $\mathrm{II}B-\mathrm{V}\mathrm{I}$ 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.