Phonon-Polariton Excitations in MgZnO/6H-SiC Structures

Abstract

Specular infrared reflection spectra in the range of “residual rays” of the film and the substrate and in the case of the E⊥c orientation of the electric field have been simulated for the first time for thin MgxZn1−xO films deposited on optically anisotropic 6H-SiC substrates. The simulation was carried out making use of self-consistent parameters obtained earlier for magnesium oxide, zinc oxide, and silicon carbide single crystals. The film thickness and the Mg content x in the film are demonstrated to considerably distort the reflection spectra and to change the reflectivity of the MgxZn1−xO/6H-SiC structure. Using the Kramers–Kronig relation, the spectral intervals, where the reflectivity is sensitive to the film thickness and to the doping levels of the film and the substrate, are determined. The main attention is paid to analyze results obtained for x = 0.2. The existence of surface polaritons in such structures is theoretically demonstrated for the first time, and the attenuated total reflectance surface I(v)/I0(v) is plotted as a three-dimensional representation of the structure transmittance dependence on the radiation frequency and the incidence angle. A possibility to study the resonant interaction of optical phonons with plasmons in the film and the substrate is demonstrated.

З’ясування умов збудження поверхневих поляритонів у кераміці Mg0,2Zn0,8O методом порушеного повного внутрішнього відбивання

“…According to Fig. 3, the DTIR spectra of Mg 0.2 Zn 0.8 O ceramics demonstrate all those features that we observed experimentally for ZnO, MgO, and 6H-SiC single crystals [3,15]; namely, a band intensity reduction for larger incidence angles of IR radiation, a substantial broadening of the SP spectrum in the region of "residual rays" for larger incidence angles of IR radiation in the DTIR prism, the asymmetric shape of the spectral minimum and its shift toward low frequencies, and others. The manifestation of minima in the DTIR spectra only in the case of 𝑝-polarized IR radiation and the negative values of the dielectric permittivity in the interval between the transverse and longitudinal optical phonon frequencies (Table 2) confirm that surface polaritons can be excited in Mg 𝑥 Zn 1−𝑥 O ceramics.…”

“…As was shown in works [3,[14][15][16][17], a variation in the concentration of free charge carriers substantially affects the reflection coefficient value in the highfrequency band of "residual rays" of the zinc and magnesium oxides (600-1500 cm −1 ), whereas the surface roughness affects the reflection coefficient in a frequency interval of 400-600 cm −1 . This difference makes it possible to distinguish the influence of surface roughness on the reflection coefficient from that of the charge carrier concentration directly from the IR reflectance spectra.…”

“…Parameters of the phonon subsystem the phonon subsystem in Mg 𝑥 Zn 1−𝑥 O, which were varied afterward when modeling the experimental spectra. Note that the plasmon-phonon interaction most clearly manifests itself in the IR reflection spectra of solid solutions at the concentrations of free charge carriers that satisfy the condition 𝜈 LO ≤ 𝜈 𝑝 [15,16].…”