Temperature and pressure dependences of the dielectric constants of semiconductors

The effects of temperature and hydrostatic pressure on the static dielectric constant () were investigated for a group of crystalline semiconductors chosen to be representative of III-V compounds (GaAs and GaP), II-VI compounds (ZnS and CdS), and group-IV (Si) materials. When combined with earlier results on the temperature and pressure dependences of the high-frequency optical (i. e. , electronic) dielectric constants (_), the present results allow, for the compound semiconductors, determination of the lattice contribution to these effects. The results are discussed from both the microscopic and macroscopic points of view. For all the crystals studied, the pressure effects are dominated by the change in polarizability with volume, and the temperature effects by anharmonicities. The pressure dependences of the lattice contributions to the dielectric constants (₁₁ and ₃₃) of hexagonal CdS are anomalous in that they increase with pressure. This behavior is most likely due to coupling between the appropriate TO modes and the TA modes which are known to soften on approaching the pressure-induced phase transition in this crystal. The transverse dynamic effective charge was calculated for the compounds, and its pressure dependence was determined for GaAs and GaP. The results and their implications are discussed.