Optical Properties of Some Compound Semiconductors in the 36-150-eV Region

Abstract

The absorption spectra of evaporated thin films of ZnS, CdS, ZnSe, CdSe, ZnTe, CdTe, PbS, and PbTe in the 36-150-eV region are reported. The measurements were performed using the DESY electron synchrotron as a radiation source. A sharp doublet associated with transitions from the $3p$ core levels of Zn to the conduction bands ($3p\ensuremath{\rightarrow}c$) is observed for ZnS, ZnSe, and less clearly for ZnTe. The splitting of this doublet seems due to spin-orbit interaction. Other less pronounced structure (Se: $3d\ensuremath{\rightarrow}c$ in ZnSe, Cd: $4p\ensuremath{\rightarrow}c$ in CdTe) is also observed, but most spectra are dominated by broad transitions similar to the atomic $d\ensuremath{\rightarrow}f$ transitions observed in this region for Kr and Xe. The number of effective electrons whose oscillator strength has been exhausted at a given energy is obtained by integrating the absorption coefficient. In the compounds containing the heavy elements Te and Pb, all outermost $d$ electrons of the core have exhausted their oscillator strength at 150 eV.