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.

Si1−x−yGexCy films ( x≊0.90, y⩽0.02) were grown by molecular beam epitaxy on Si substrates. Infrared optical absorption was used to obtain the band gap energy at room temperature. Biaxial strain obtained from x-ray diffraction measurements verified the presence of nearly relaxed films, and the total and substitutional C contents were obtained from channeling C-resonance backscattering spectrometry. We show by direct measurements that interstitial C had a negligible impact on the band gap, but substitutional C was found to increase the band gap with respect to equivalently strained Si1−xGex alloys. While strain decreases the band gap, the effect of substitutional C on the band gap depends on the Si and Ge fractions.

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We have applied a virtual crystal approximation to the linear combination of atomic orbitals method to calculate critical point energies of unstrained Si1−x−yGexCy alloys spanning the composition parameter space. Additionally, we have calculated the band structure across the Brillouin zone for a series of alloy compositions. We found the band energies had significant bowing departures from linearity throughout the system. In some cases, the energy band gap was not monotonically dependent on composition. Our theoretical results are compared with recent experimental results, and good agreement was found overall.

Spectroscopic ellipsometry was used to measure the dielectric functions of epitaxial and bulk Ge at photon energies from 1.5 to 5.2 eV. The epitaxial Ge was grown at 400°C by molecular beam epitaxy on ͑001͒ Si substrates. The optical response and the interband critical-point parameters of Ge on Si were found to be indistinguishable from that of bulk single crystal Ge, indicating high optical quality. Dislocation density measurements using an iodine etch verified low surface defect densities. We conclude that epitaxial Ge grown on Si at relatively low temperatures is suitable for optical device applications.

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Group IV semiconductor alloy systems offer promise as variable band gap alloys compatible with Si technology. Binary, ternary, and quaternary group IV alloys were grown by molecular beam epitaxy on Si substrates. The fundamental absorption edge was measured by Fourier transform infrared spectroscopy to obtain the optical band gap of the alloys, and the position of the fundamental absorption edge was observed to depend on the experimentally measured alloy composition. Our results indicate a variety of Si-rich group IV alloys with various band gaps are experimentally producible.