Nanoplasmonics and surface enhanced spectroscopy

Effect of chemical composition and thickness of MgxZn1-xO films on plasmon-phonon interaction in MgxZn1-xO/6H-SiC structures
A. Marushenko1, O. Melnichuk2, L. Melnichuk2,
Ye. Venger3, N. Korsunska3, L. Khomenkova1,3

1 National University “Kyiv-Mohyla academy”, Department of Physics and Mathematics, Faculty of Natural Sciences, 2 Skovorody str., Kyiv 04070, Ukraine
2 Mykola Gogol State University of Nizhyn, 2 Hrafska Str., Nizhyn 16600, Ukraine
E-mail: mov310310@gmail.com
3V.Lashkaryov Institute of Semiconductor Physics at the NASU, 41 Pr. Nauky, Kyiv 03028, Ukraine

MgxZn1-xO offer unique properties such as high photosensitivity, high photo- and cathodoluminescence yields, piro- and piezoelectric effects, etc. In this work the MgxZn1-xO films prepared on 6H-SiC substrates by electron-beam evaporation method were investigated by means of surface polariton (SP) and infrared reflection (IRR) spectroscopy in the range of residual rays of the film and substrate (400-1200 cm-1) versus film composition and thickness for orientations E⊥C and E||C at room temperature.
It was observed that the films with x>0.2 showed cubic lattice structure, whereas the films with x≤0.2 demonstrated hexagonal lattice structure and anisotropic optical properties in the IR spectral range. Besides, the electron concentration in the film was found to vary with x in the range 1×1016-5×1018 cm-3.
To simulate IRR and SP spectra, the mathematical model with additive and phenomenological contribution of oscillators to dielectric permittivity of the materials was developed. The orientation of the optical axis in the film and the substrate as well as the phonon and plasmon-phonon interactions in the film and substrate, respectively, were considered. For the first time, the surface polariton spectral range and dispersion laws as well as corresponding damping coefficients were determined. For the MgxZn1-xO film, the frequencies and damping coefficients of the TO and LO modes of all oscillators, the dielectric contribution of each mode, static and high-frequency dielectric permittivity for orientations E⊥C and E||C were obtained with high accuracy. It was shown that for the films thinner 90 nm, more precise information can be extracted from the SP spectra, whereas for the thicker films (≥5 μm) the IRR spectroscopy is more useful. The results obtained showed that proposed non-destructive method can be implemented for the determination of optical properties of other semiconductor films.
This work was supported by the Ministry of Education and Science of Ukraine (project 89452).