Optical Properties of Single-Crystal Cadmium

Measurements were made of the reflectivity and/or absorptivity of cadmium from 0.15 to 20 eV, using polarized light with the electric vector both perpendicular and parallel to the $c$ axis of the crystal. In the visible and infrared spectra both polarizations yielded strong absorption peaks. For perpendicular polarization, the main peak was at 0.98 eV and was attributed mainly to transitions between bands along the $L-H$ symmetry line. Also in this polarization there was an absorption edge at 0.29 eV. This may be due to transitions near the point $K$ in the Brillouin zone. For parallel polarization, the main absorption peak was at 1.10 eV and was attributed to transitions between bands along $\Gamma -K$, $\Gamma -M$, and $L-H$. No low-energy absorption edge was found for parallel polarization. Agreement between the experimental data and the calculations of Kasowski based on a nonlocal-pseudopotential model was fairly good. There was no agreement between the data and calculations based on a local-pseudopotential model. At low temperatures, the long-wavelength absorptivities were approximately constant, in agreement with theory for the anomalous-skin-effect region. Using the theory of Kliewer and Fuchs and the experimental data, parallel and perpendicular effective masses were calculated to be $1.09m_0$ and $1.61m_0$, respectively. The weighted average of these is in good agreement with the thermal effective mass for cadmium. The low-energy data support the theory of Kliewer and Fuchs and tend to confirm the volume absorption process suggested by Holstein.