Use of hybrid phenomenological and statistical effective-medium theories of dielectric functions to model the infrared reflectance of porous SiC films

The reflectance of porous silicon carbide (PSC) thin films on SIC substrate s is measured in the infrared reststrahlen region by Fourier transform infr ared reflectance spectroscopy and is compared to simulated spectra based on phenomenological and Bergman statistical effective-medium dielectric funct ions. The phenomenological models evaluated include the Bruggeman, cavity- and sphere-Maxwell-Garnett (C-MG and S-MG), Landau-Lifshitz/Looyenga (LLL), and Monecke models. In addition, modifications to the Bruggeman and C-MG m odels with variable particle shapes and surface layers are examined. Hybrid versions of the C-MG and LLL models are also considered, alternatively by using a phenomenological mixing approach, which gives a direct physical int erpretation of the topology, and by directly mixing the statistical spectra l density functions of the C-MG and LLL effective dielectric functions. Thi s latter statistic:al hybrid model gives the best (and quite good) agreemen t with experiments. The differences in the hybrid models are understood by comparing their spectral density functions. The dip (or splitting) in the P SC film reststrahlen band is attributed to surface optical phonon modes.