IR surface polariton spectroscopy as a method for studying the optical properties of ultra thin films

Abstract

Abstract.Experimental results of investigation of optical properties of MgO thin films (thickness 10, 30, 100 и 300 nm) and AlN films (thickness 40 и 400 nm) on sapphire substrate are discussed. The optical phonon frequencies of these films are located in frequency region of surface polariton of sapphire. Due to the resonance between them the splitting and the shift of absorption spectra of sapphire surface polariton appear. From these experimental data it is possible to reconstruct all constants of the permittivity of both the film and substrate, the film thickness, and to specify its structure.To use thin semiconductor films in a variety of applications, including optoelectronics, need to know their physical properties. In most cases the film properties are very different from the properties of bulk materials from which they are made. To study the physical (optical) properties of ultrafine (nanometer) films still no spectrometers required photometric accuracy. In some cases, to determine the physical parameters of nanofilms useful surface polariton spectroscopy.Surface polaritons (SP) are nonradiative electromagnetic excitations at the interface of two media, propagating along the interface, if the dielectric constant of the contacting materials have different signs [1][2][3][4]. Electromagnetic field of SP focuses directly from the media interface, and decreases exponentially with distance from the interface (near field), so that the SP is very sensitive to the characteristics of the interface. If the frequency of the optical phonons of the film lies in the region of existence of SP substrate, then, by the resonance between them, there is a splitting of the bands and a shift of the absorption spectra of SP substrate. From these experimental data can be restored all constant permittivity and the thickness of the film, and thus to characterize the film properties. The resulting gap in this dispersion curves of SP substrate is proportional to the square root of the thickness of the film that allows you to measure the thickness of very thin films [1,[5][6][7][8][9]. The report discusses the experimental results on the optical properties of the films of MgO (thickness 10, 30, 100 and 300 nm) [5,7,9] and films of AlN (thickness of 40 nm and 400 nm) on sapphire [6][7][8][9]. SP spectra were measured in attenuated total internal reflection