Small-Angle Oblique-Incidence Infrared Reflection in Polar Materials: II. Experiment on ZnO

The properties of polar optical phonons in thick single crystals of semi-insulating ZnO have been studied experimentally by infrared small-angle oblique-incidence reflectometry (SAOIR) with the subsidiary measurement of Raman scattering. The infrared light used is s- or p-polarized and incident to the c-face of the crystals at an angle of 10. Despite such a small angle of incidence, since the principal components of the dielectric tensor are very small around the frequencies of longitudinal optical (LO) phonons, Snell’s total reflection and Brewster’s null reflection take place contiguously to modify the reststrahlen band. Consequently, a pair of line structures due to LO phonons of A1 and E1 modes appear in the difference spectrum between the s and p spectra. Analysis of the results in terms of Kuroda and Tabata’s theory of SAOIR using the dielectric function of Gervais and Piriou’s four-parameter semi-quantum oscillator model provides accurate frequencies and damping energies of all the LO and transverse optical (TO) phonons