Metastable Ge 1Ϫy C y alloys were grown by molecular beam epitaxy as homogeneous solid solutions having a diamond lattice structure. The substrates were ͑100͒ oriented Si wafers and the growth temperature was 600°C. We report on measurements of the composition, structure, lattice constant, and optical absorption of the alloy layers. In thick relaxed layers, C atomic fractions up to 0.03 were obtained with a corresponding band gap of 0.875 eV. These alloys offer new opportunities for fundamental studies, and for the development of silicon-based heterostructure devices.

We have carried out x-ray photoelectron spectroscopy on diamond thin films deposited by microwave assisted chemical vapor deposition technique using a H2-CH4 plasma. Films grown for different lengths of time, from 1 min to several hours, were analyzed for the surface composition in the C 1s and Si 2p regions. The results indicate the presence of SiC in the initial stage of nucleation due to the carbon interaction with the Si substrate. Graphite starts to form in early stages of nucleation as the substrate becomes supersaturated with carbon. A diamond peak starts to appear after the incubation period and a simultaneous decrease in the carbide and graphite peak intensities was observed. Graphite is preferentially etched during the growth but SiC remains as an impurity even after several hours of deposition.

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