Quality of a-Si: H/Si₃N₄ multilayer films fabricated by double tubed coaxial line type MPCVD system and application of the films to optical circuit element

The object of this research was the fabrication of high-quality a-Si:H/Si₃N₄ multilayer films with ultrathin multilayered configurations to serve as a new photonic material, as well as the evaluation of the film quality and applications to photonics. The authors have succeeded in controlling the thickness of the multilayer film at subnanometer order as indicated by the X-ray diffraction peak of the a-Si:H/Si₃N₄ multilayer film. The theoretical curve and the experimental results for the optical energy band gap agree well for multilayer films fabricated by varying the thickness of the a-Si:H layer while the thickness of the Si₃N₄ layer is kept constant, and hence excellent multilayer films are obtained. These multilayer films are applied to optical waveguides. The optical waveguide with an ultrathin multilayer structure, much thinner than the wavelength λ of the guided light, is expected to exhibit an anomalous propagation characteristic. It is found that the TM mode is transmitted while the TE mode is cut off in the present multilayer slab waveguide.