The goal of this study is to investigate the effect of carbon incorporation upon thermal oxidation of Si1−xGex alloys and its role on strain compensation in Si1−xGex alloys. Si1−xGex and Si1−x−yGexCy alloys on Si(100) are grown by combined ion and molecular beam deposition and are then oxidized at 1000 °C in a dry oxygen ambient for two h. The thickness and the composition of all samples before and after oxidation are measured by Rutherford backscattering spectrometry (RBS) combined with ion channeling at 2.0 MeV and carbon nuclear resonance analysis at 4.3 MeV using 4He++ ions. In agreement with previously reported results of dry oxidation on Si1−xGex thin films, 2.0 MeV RBS analysis shows that a layer of SiO2 is formed on the top surface of both Si1−xGex and Si1−x−yGexCy thin films, while Ge segregates towards the top surface and at the SiO2/Si1−xGex and SiO2/Si1−x−yGexCy interfaces. However, it is observed for the first time that dry oxidation rates of Si1−xGex thin films decrease with increasing Ge fraction x for x≳0.20 and with increasing minimum yield. Ion channeling analysis and strain measurements indicate that the incorporation of C rather than the amount of C itself affects the dry oxidation mechanism because of its strong influence on film strain and crystalline quality. These results are discussed in conjunction with observations by secondary ion mass spectrometry, high resolution transmission electron microscopy, Fourier transform infrared spectrometry, and tapping mode atomic force microscopy.
The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1−x−yGexCy on Si(100), has been investigated. The epitaxial quality of Si1−x−yGexCy is found to be inferior to that of Si1−xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank–van der Merwe to Stranski–Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1−x−yGexCy material, as determined by Vegard’s law, and the equilibrium Si–C bond length, weakens the Si–C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1−x−yGexCy films with increasing C incorporation suggests a repulsive Ge–C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 °C, whereas at 450 °C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized.
An upper temperature limit of 450 °C has been established for growth of heteroepitaxial Si1−x−yGexCy solid solutions with substitutional C on Si(100) by combined ion and molecular beam deposition (CIMD). At 450 °C infrared absorption spectroscopy shows that C is on substitutional sites and no SiC precipitates are detected, whereas at 560 °C the substitutional C signal is much smaller but SiC precipitates are still not detected. High resolution transmission electron microscopy shows that Si1−x−yGexCy films deposited at 560 °C exhibit Ge deficient, coherent, secondary phase clusters in the cubic diamond matrix, which are not seen in films deposited at 450 °C. These observations suggest that the clusters are C-rich, Ge-deficient precursors to SiC, with a lattice which is distorted but free of extended defects. Ion channeling results indicate that the Si1−x−yGexCy films might have a distribution of different bond lengths.
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