Optical Properties and Band Structure of Wurtzite-Type Crystals and Rutile

The fundamental reflectivity of several optically anisotropic materials (hexagonal ZnS, CdS, CdSe, and rutile) has been measured at room temperature with linearly polarized light of wavelength longer than 1100 \AA{}. Measurements were performed with the electric vector parallel and perpendicular to the $c$ axis of the crystal. From these reflection measurements, extended with unpolarized light to the region between 1100 and 550 \AA{}, the optical constants have been determined by means of the Kramers-Kronig technique. The structure in the optical data of the wurtzite materials is interpreted in terms of the electronic band structure as due to direct allowed interband transitions. The interpretation is based on the existing knowledge about the related zincblende and diamond-type materials and the fact that the band structure of wurtzite along the $c$ axis can be derived from that along the [111] axis of zincblende by applying a small hexagonal crystal field as a perturbation. The optical data on rutile reflect the ionic character of the material.