Synthesis and characterization of heteroepitaxial diamond-structured Ge1-xCx (x=1.5-5.0%) alloys using chemical vapor deposition

We report growth of high quality heteroepitaxial Ge1-xCx alloys on Si(100) with C concentrations ranging from 1.5 to 5 at %. The materials were obtained by reactions of the novel methylgermanes CH3GeH3 and HC(GeH3)3 with GeH4 at 470°C using ultrahigh-vacuum chemical-vapor deposition techniques. The crystallinity, composition, and microstructure of the films were characterized by Rutherford backscattering, carbon-resonance spectroscopy, and cross-sectional transmission electron microscopy. Ge1-xCx (x=0.015-0.030) materials were deposited using CH3GeH3 and displayed excellent crystallinity. Films with higher C content were deposited using HC(GeH3)3. These films were epitaxial and of high crystallinity but they also displayed interfacial defects which sometimes persisted through the entire layer. Electron diffraction data and carbon-ion channeling experiments indicated that carbon primarily occupied substitutional sites in the Ge diamond-cubic lattice. Secondary ion mass spectrometry revealed that the films were pure and highly homogeneous.