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 Si1-x-yGexCy materials. Thin films with composition Si0.37Ge0.13C 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-yGexCy (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. © 1994 American Institute of Physics.