D. C. Electrical Conductivity of Si₃N₄-SiC Films Prepared by Plasma CVD

Abstract

The D. C. electrical conductivity of nano-composite Si₃N₄-SiC films prepared by the plasma CVD method at 400°C was measured by the three-terminal technique. It was estimated that the electrical conduction in Si₃N₄ films was due to the hopping mechanism which gave the ohmic characteristics and Poole-Frenkel mechanism below and above the electric field of 9×10⁶V⋅m^-1, respectively. The electrical conduction in SiN_1.01C_0.28 (abbreviated as ‘SiNC’) and SiC films was estimated to show the hopping mechanism under the whole field studied. The activation enemies of coduction for Si₃N₄, SiNC and SiC films were approximately 0.72, 1.64 and 0.43eV, respectively at about 130°C; the SiNC film showed an extremely high value. The activation energies of these films were much lower than the optical band gaps (2.7-5.3eV). The electrical conduction in the compositional range from Si₃N₄ to SiC at a constant temperature showed a maximum near the atomic ratio (C/Si) of 0.3 without obeying the theory of composite. This was assumed that the electrical conduction of the SiN_xC_y films was influenced by the difference in number of valence electrons between N and C and the structural change from Si₃N₄ to SiC since N and C atoms around Si were mixed uniformly on an atomic scale.