Novel chemical routes to silicon-germanium-carbon materials

We report the use of novel molecular precursors and ultrahigh vacuum chemical vapor deposition techniques to synthesize solid solutions of cubic SiC-GeC and diamond-structure Si_1-x-yGe_xC_y materials. Thin films with composition Si_0.37Ge_0.13C _0.50 were deposited on Si by thermal decomposition of Ge[Si(CH ₃)₃]₄ at 650-700°C. Electron microscope observations showed a polycrystalline zinc-blende-type structure and infrared (IR) analyses revealed carbide-type Si-C and Ge-C vibrations. The Si _1-x-yGe_xC_y (y≳2%) alloys were deposited at 550-600°C on Si and SiO₂ by interactions of (1) C(SiH ₃)₄ and GeH₄; (2) CH₃GeH₃ and SiH₄; and (3) CH₃GeH₃ with mixtures of GeH₄ and SiH₄. A homogeneous alloy phase of composition Si₅₆Ge₃₀C₁₄ with diamond cubic structure was obtained from reaction 1. Reactions 2 and 3 produced films with carbon compositions ranging from 2 to 27 at. %. The materials containing less than 10% carbon appeared to be exclusively diamond cubic, whereas those with greater carbon compositions showed mixtures of diamond cubic and carbide phases as indicated by vibrational and structural characterization. Secondary ion mass spectrometry experiments revealed that all materials had excellent chemical purity.