Chemical Synthesis of Metastable Germanium-Carbon Alloys Grown Heteroepitaxially on (100) Si

High-quality diamond-structured Ge_1-xC_x alloys have been grown on (100) Si using ultrahigh-vacuum chemical vapor deposition techniques and novel chemical precursors. Two-dimensional growth of single-crystal heteroepitaxial layers (30-120 nm thick) of germanium-carbon alloys with carbon concentrations up to 7% has been achieved by reactions of GeH₄ with germylmethanes, (GeH₃)_4-xCH_x (x = 1-3), at 470 °C. The composition of the materials was established by extensive Rutherford backscattering (RBS) carbon resonance analysis, and the layer crystallinity was characterized by cross-sectional transmission electron microscopy and RBS channeling experiments. RBS ion channeling revealed that the carbon primarily occupied substitutional sites in the diamond-like Ge lattice. Alloys with low carbon content displayed virtually perfect crystallinity whereas materials with high carbon incorporation had structural defects in the form of {111} stacking faults and microtwins. The thin film microstructure of a given alloy composition was independent of the precursor, but the efficiency of carbon incorporation increased dramatically as the number of GeH₃ moieties in the precursor increased. Further characterization by Auger electron spectroscopy and secondary ion mass spectrometry showed that the materials were pure and highly homogeneous, and electron energy loss spectroscopy indicated sp³ hybridized diamond-like carbon. The synthesis and characterization of novel (trihalogermyl)methane compounds such as (Br₃Ge)₃CH and (Cl₂XGe)₂CH₂ (X = Cl, Br, or I) and their reactions with LiAlH₄ to produce the corresponding hydrides is also reported.