Asymmetric peak line shape of infrared dielectric function spectra for thermally grown silicon dioxide films

Measured infrared dielectric function spectra ranging from 300 to 1400 cm(-1) for thermally grown silicon dioxide films were studied. The dielectric function spectra were calculated by requiring the calculated spectra to fit to the actual spectra. The peak line shape of the dielectric function can be described by a Gaussian distribution, but not by a Lorentzian line shape. In detail, frequencies of half height for the imaginary part of the dielectric function of high- and low-frequency edges are not actually symmetrical. According to interpretations based on a central and noncentral force network model, the asymmetric distribution of the dielectric function arises from the symmetrical distribution of the bond angles of a random network of the SiO4 tetrahedra. For that reason, we developed a dielectric function model which can describe an asymmetrical Gaussian line shape. This asymmetric Gaussian model minimizes the number of parameters needed, which are the one center position and low- and high-Gaussian distribution widths, compared with the assignment method for multiple purely Gaussian peaks. (C) 2000 American Institute of Physics. [S0021- 8979(00)01301-9].